Item 7 - Appendix 1
West Dunbartonshire Council · 19 August 2026
Back to Infrastructure, Regeneration & Economic Development Committee — 19 August 2026 and its agenda
Text extracted from the council's PDF. Layout and reading order may differ from the original.
Page 1
AtkinsRéalis - Baseline / Référence CLYDEBANK SURFACE WATER MANAGEMENT PLAN SWMP West Dunbartonshire Council 16th July 2026 ITEM 7 - APPENDIX 1
Page 2
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 2 AtkinsRéalis - Baseline / Référence Notice This document and its contents have been prepared and are intended solely as information for West Dunbartonshire Council and use in relation to Draft for comment AtkinsRéalis UK Limited assumes no responsibility to any other party in respect of or arising out of or in connection with this document and/or its contents. This document has 97 pages including the cover. Document history Document title: Clydebank Surface Water Management Plan Revision Purpose description Originated Checked Reviewed Authorised Date 1.0 Draft for comment HP AD CA - 30/04/2024 2.0 Client comments HP AW BC ZT 16/07/2026 Client signoff Client West Dumbartonshire Council Project SWMP Job number Client signature/date
Page 3
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 3 AtkinsRéalis - Baseline / Référence Contents 1. Introduction ............................................................................................................................................... 5 1.1 Legislative Background .................................................................................................................. 5 1.2 Area Specific Background .............................................................................................................. 5 1.3 Potentially Vulnerable Area Summary ........................................................................................... 6 1.4 Surface Water Management Plan Stages...................................................................................... 6 1.5 Catchment Background.................................................................................................................. 7 2. Data Collection and Gap Analysis .......................................................................................................... 8 3. Methodology ............................................................................................................................................. 9 3.1 Steps .............................................................................................................................................. 9 3.1.1 Define Catchment Extent (Step 1) ................................................................................................. 9 3.1.2 Review of Historical Flood Data (Step 2) ..................................................................................... 10 3.1.3 Define Hotspots (Step 3) .............................................................................................................. 11 3.1.4 Hotspot Delineation (Step 4) ........................................................................................................ 13 3.1.5 Hotspot Interactions ..................................................................................................................... 14 4. Improved Understanding of Flood Risk ............................................................................................... 16 4.1 Root Cause Analysis Summary ................................................................................................... 16 4.2 Root Cause Analysis: Desktop .................................................................................................... 18 4.2.1 Second Avenue / Ramsey Street ................................................................................................. 18 4.2.2 Western Isles Road ...................................................................................................................... 19 4.2.3 Duntocher Road ........................................................................................................................... 19 4.2.4 Livingstone Street ........................................................................................................................ 20 4.2.5 Melbourne Avenue ....................................................................................................................... 21 4.2.6 Low Crescent ............................................................................................................................... 22 4.2.7 Dumbarton Road .......................................................................................................................... 22 4.2.8 Dunedin Terrace .......................................................................................................................... 23 4.2.9 Kilbowie Road .............................................................................................................................. 24 4.2.10 Station Road ................................................................................................................................ 25 4.3 Root Cause Analysis: Modelling .................................................................................................. 26 4.3.1 1D Sewer Network Modelling ....................................................................................................... 26 4.3.2 Pluvial Only Flood Modelling ........................................................................................................ 38 4.3.3 Integrated 1D - 2D Runoff Model ................................................................................................. 47 4.3.4 Model Limitations ......................................................................................................................... 57 4.3.5 Future Flood Risk ......................................................................................................................... 57 5. Set Objectives ......................................................................................................................................... 59 6. Option Appraisal ..................................................................................................................................... 61 6.1 Scoping Option Appraisal............................................................................................................. 61 6.2 Options Assessed ........................................................................................................................ 63 6.2.1 Non-Structural .............................................................................................................................. 63 6.2.2 Structural ...................................................................................................................................... 65 6.2.3 Property Level Protection ............................................................................................................. 66 6.2.4 SuDS Types ................................................................................................................................. 67 6.3 Develop Preferred Option / Screening ......................................................................................... 70 6.3.1 Second Avenue / Ramsay Street ................................................................................................. 70 6.3.2 Western Isles Road ...................................................................................................................... 72 6.3.3 Duntocher Road ........................................................................................................................... 73 6.3.4 Livingstone Street ........................................................................................................................ 75 6.3.5 Melbourne Avenue ....................................................................................................................... 76 6.4 Prioritising Options ....................................................................................................................... 78 6.4.1 Second Avenue / Ramsay Street ................................................................................................. 79 6.4.2 Western Isles Road ...................................................................................................................... 80 6.4.3 Duntocher Road ........................................................................................................................... 81 6.4.4 Livingstone Street ........................................................................................................................ 82 6.4.5 Melbourne Avenue ....................................................................................................................... 83 6.5 Baseline: ‘Do minimum’................................................................................................................ 84 6.6 Options: ‘Do something’ ............................................................................................................... 84
Page 4
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 4 AtkinsRéalis - Baseline / Référence 7. Develop preferred option: confirm funding ......................................................................................... 86 8. Conclusions ............................................................................................................................................ 89 8.1 Recommendations ....................................................................................................................... 91 Appendix A. Objectives .................................................................................................................................. 94
Page 5
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 5 AtkinsRéalis - Baseline / Référence 1. Introduction AtkinsRéalis was commissioned by West Dunbartonshire Council (WDC) in 2023 to undertake a Surface Water Management Plan (SWMP) for the Clydebank catchment. The initial SWMP was completed and submitted in April 2024, based on the best available information at that time, including SEPA Flood Maps, historical flood records, stakeholder information and hydraulic modelling outputs. Following submission of the report, a stakeholder workshop was held in December 2025, with representatives from WDC, Scottish Water (ScW), Network Rail and Scottish Canals to discuss flooding mechanisms, ongoing investigations, known data gaps and opportunities for collaboration across the catchment. In addition, the release of the updated 2025 SEPA Flood Maps provided a revised understanding of surface water flood risk, resulting in notable changes to the extent and significance of flooding predicted at a number of hotspot locations. This report revisits the original SWMP findings considering the updated flood mapping, stakeholder feedback and ongoing investigations to provide an updated understanding of flood risk within the Clydebank catchment. The review identifies where the understanding of flood mechanisms has changed, highlights key uncertainties and knowledge gaps, and makes recommendations for future investigation and flood risk management activities. It should be noted that the flood management options developed as part of the original SWMP have not been revisited or remodelled as part of this update. Consequently, the options should be considered in the context of the improved understanding of flood risk now available, considering the need for a collaborative approach in the catchment and reviewed before any future progression to detailed appraisal or implementation. 1.1 Legislative Background Under the Flood Risk Management (Scotland) Act 2009, all Local Authorities are required to develop a SWMP for the areas as outlined in SEPA’s Flood Risk Management Plan (FRMP) document which fall under their responsibility. These plans need to assess the objectives set out in the FRMP. The actions typically include identifying and assessing the risk of surface water flooding in the urban areas and proposing a course of action for the next steps to reduce the flood risk through a risk-based approach. This assessment includes considering present and future flood risk. 1.2 Area Specific Background Clydebank was outlined as an area requiring a Sewer Flood Risk Assessment to be completed in Cycle 2 of the FRMP (2022 – 2028) in the Clyde 2. This involves the volume of water that would overwhelm the sewer system and cause flooding from manholes or inside homes to be assessed, to support understanding the performance of the urban drainage network. ScW will complete this assessment within the highest priority sewer catchments, this includes the Dalmuir catchment. This will help improve knowledge and understanding of potential surface water flood risk. Clydebank was outlined as requiring a SWMP to be completed after Cycle 2. The indicative timescales are after June 2028. The specific action reference is 54021. The additional information uncovered in the Sewer flood risk assessment and through developments in flood risk management planning between 2022-2028 should be considered when this commences. The specific action outlined was “Areas at risk of heavy or prolonged rainfall causing flooding due to water ponding on man-made surfaces or overwhelming the drainage system are to be identified. This priority area will provide a baseline for the identification of next steps in managing water ponding or over-whelmed drainage systems. This should guide adaptive planning to allow for the impacts of climate change to be monitored, understood, and managed”. This report will therefore: 1 Flood risk management plans 2021 (sepa.org.uk)
Page 6
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 6 AtkinsRéalis - Baseline / Référence Summarise the areas identified as being at risk of flooding because of water ponding caused by heavy or prolonged rainfall within the urban catchment. Select priority areas based on the outcomes of a multi-criteria assessment. Set out the next steps. 1.3 Potentially Vulnerable Area Summary The Potentially Vulnerable Area (PVA) is situated in Clydebank, which is located on the River Clyde within the West Dunbartonshire local authority area (refer to Figure 1-1). This area is most at risk from surface water and sewer flooding. However, there is also a risk of river and coastal flood risk from the tidally influenced River Clyde. According to the Local Flood Risk Management Report there are approximately 1,800 people at risk of flooding and approximately 1,200 homes and businesses. This is estimated to increase to 2,700 people and 1,700 homes and businesses by 2080 due to climate change.2 Figure 1-1 - Map showing Clydebank PVA defined by SEPA 1.4 Surface Water Management Plan Stages To help develop the SWMP, this report follows the structure set out in the stages of SWMP wheel (see Figure 1- 2) outlined in the Scottish Government’s SWMP Guidance (2018).3 This outlines the stages when developing a surface water management plan to ensure a plan is developed in accordance with the Flood Risk Management (Scotland) Act 2009. 2 https://www.west-dunbarton.gov.uk/media/ewmdtdtz/local-flood-risk-management-plan-2022-2028.pdf 3 2 The surface water management planning process - Surface water management planning: guidance (2018) - gov.scot (www.gov.scot)
Page 7
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 7 AtkinsRéalis - Baseline / Référence Figure 1-2 - Stages of Surface Water Management Plan Process (Scottish Government) This study follows the ‘Develop Plan’ phase of the SWMP wheel stages. This includes: Prepare: data collection and desktop analysis of flooding records and SEPA flood maps Understand flood risk: this will build and improve on the initial understanding of flood risk by developing hydraulic models to inform root causes analysis. Set objectives: establish an understanding of the key objectives the Council have for development of the SWMP, based on the increased understanding of flood risk in the hotspot areas. Option appraisal: high-level assessment of potential mitigation opportunities Option development: refinement of indicative opportunities identified Future actions and stakeholder engagement: Summarize key findings, recommendations and outputs and include proposals for monitoring. 1.5 Catchment Background Clydebank is a town situated just 10km northwest of Glasgow City Centre. The town is situated on the north bank of the River Clyde, which flows from southeast to northwest. Clydebank is bound to the north by the Kilpatrick Hills, which reach a height of approximately 400m. The area was largely rural until the end of the 19th century, when the growth of the shipbuilding industry on the river led to the foundations of Clydebank. Today, Clydebank is heavily urbanised and has a population of approximately 26,220. 4The town is served by the Dalmuir sewage network. 4 https://www.west-dunbarton.gov.uk/media/w50dczjc/clydebank-data-pack-final.pdf
Page 8
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 8 AtkinsRéalis - Baseline / Référence 2. Data Collection and Gap Analysis A critical element of a SWMP is the accuracy of the data collected and the analysis. Data shared by stakeholders was reviewed for quality, accuracy, completeness and to understand if there were any gaps in the provided data and how the lack of this data would impact the confidence in outputs of this project. Table 2-1 summarises the data requested and how it was used in the study to assess flood risk. Data Source Study Purpose OS MasterMap West Dunbartonshire Council Plan production / reporting and study planning OS OpenMap (Building Outlines) Open-Source Data To aid identification of flooding hotspots Ground Data (LiDAR data). 1m resolution. National LiDAR Programme – data.gov.uk Produce a Digital Terrain Model (DTM) of the study area National Receptor Database SEPA Assess properties that are at medium or high surface water flood risk as outlined by SEPA Flood Maps SEPA Flood Maps Extents SEPA To aid identification of flooding hotspot areas based on where the SEPA medium and high-risk flood maps intersected National Receptor Data building centroids or OS Building maps Hydraulic Models (1D Sewer Model – ICM Model: DOA000333 Dalmuir Current v24) ScW To aid root cause analysis of flooding, determining engineered subcatchments to hotspots, and more detailed integrated modelling Hydraulic Model Maintenance Report ScW Provides additional background information in relation to the model build, model calibration and verification. Historic Flooding Records (GIS format)/ Hotspot Data West Dunbartonshire Council To assist in identification of flooding hotspot areas and in root cause analysis Information on flooding from the sewer network ScW To assist in identification of flooding hotspot areas and in root cause analysis Table 2-1 - Data Requested and Usage
Page 9
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 9 AtkinsRéalis - Baseline / Référence 3. Methodology 3.1 Steps A methodology was developed to understand surface water flood risk within Clydebank. This methodology is summarised in Table 3-1 Error! Reference source not found.and explained in more detail in the subsequent sections of the report. Step Process Why? 1 Define Catchment Extent Delineate natural watershed contributing flows to PVA to determine ‘area of interest’ To identify the catchment extent that may be contributing flows to the PVA target areas and the area where the 'hotspot' will be identified. 2 Review of historical flooding data To support understanding of catchment issues and help define flooding ‘hotspots’. 3 Define 'Hotspots' Using SEPA flood maps identify the most at-risk areas within the 'area of interest' to help understand the worst-hit flooding areas within the catchments and obtain an initial understanding of where funding may be targeted. 4 Hotspot Delineation Define Natural Watershed for each hotspot area. Define engineered catchment for each hotspot area. To identify the catchment extent that may be contributing flows to each individual 'hotspot' area. To identify the engineered catchment conveying flows to each individual ‘hotspot’ areas. Mitigation measures will likely be installed upstream to help mitigate flooding at the downstream location. Therefore, we must understand the area in which measures could be installed. 5 Root Cause Analysis To understand the origin of flooding at the hotspot to quantify the extent of the issue and establish the potential interaction of different causes of flooding and what actions are needed to mitigate this flooding. Table 3-1 - Methodology Steps 3.1.1 Define Catchment Extent (Step 1) The natural watershed for the PVA Action area was obtained because this would be used as the initial pluvial extent (‘area of interest’). This was to ensure that the assessment was accounting for all natural flows that may contribute to the SWMP extent.
Page 10
Clydebank Surface Water
Management Plan_For Submission
07_26
1.0 | 16th July 2026 10
AtkinsRéalis - Baseline / Référence
Figure 3-1 shows the ‘area of interest’ in relation to the Clydebank PVA.
Figure 3-1 - Map showing the area that naturally drains via gravity towards the PVA target areas ('area
of interest')
3.1.2 Review of Historical Flood Data (Step 2)
Historical flood information was reviewed to support the understanding of flood risk and flood mechanisms within
the study area. Following the initial submission, a stakeholder workshop was held in December 2025 with
representatives from WDC, ScW, Network Rail and Scottish Canals to discuss known flooding issues and provide
additional local knowledge. This information has been used throughout the updated assessment to validate
hotspot identification and improve understanding of the factors contributing to flooding.
The following sections summarise the available historical flooding information. A desktop review of the historical
flood records, stakeholder information and supporting datasets was undertaken to identify likely flooding
mechanisms and contributing factors at each location. The findings of this assessment are summarised within
Section 4.2 – Root Cause Analysis, which presents the evidence used to develop an understanding of the causes
of flooding at each hotspot and to assess the implications of the updated 2025 SEPA Flood Maps on the original
SWMP findings.
3.1.2.1 West Dunbartonshire Council
The WDC flood records were used to help validate areas identified as being susceptible to flooding and to provide
additional insight into local flood mechanisms. In particular, the records assisted in distinguishing between
locations affected primarily by surface water flooding and those influenced by interactions between surface water,
watercourses and sewerage infrastructure. The information also helped identify locations where flooding has
resulted in impacts to residential properties, transport infrastructure and access routes.Page 11
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 11 AtkinsRéalis - Baseline / Référence 3.1.2.2 Scottish Water Historical flood information was obtained through engagement with ScW, including the workshop held in December 2025 and subsequent discussions relating to individual hotspot locations. This information was supplemented by a review of the hydraulic model. Collectively, these sources provided valuable insight into previous flooding incidents, known sewer network constraints, ongoing investigations and potential flood mechanisms across the study area. 3.1.3 Define Hotspots (Step 3) As part of the initial assessment undertaken for the first submission of the SWMP, potential surface water flood risk was identified using the SEPA flood maps available at the time. Surface water flooding, otherwise referred to as pluvial flooding, occurs when rainfall-generated runoff is unable to infiltrate into the ground or enter a watercourse, drainage system or sewer network, resulting in water collecting on the surface or flowing overland. SEPA flood maps assess flooding associated with severe rainfall events for the following annual exceedance probabilities (AEP): 1 in 10 year (10%) Annual Exeedance Probability (‘High’ likelihood); 1 in 200 year (0.5%) Annual Exeedance Probability (‘Medium’ likelihood); and 1 in 1000 year (0.1%) Annual Exeedance Probability (‘Low’ likelihood). Hotspots were identified as areas containing six or more residential and/or non-residential properties located within the SEPA medium-likelihood (0.5% AEP) surface water flood extent. In addition, locations identified by WDC where flooding could result in significant disruption to transport, access for emergency services, or wider economic activity were also designated as hotspots, regardless of the number of properties affected. Hotspot polygons were delineated to encompass the full extent of the mapped surface water flooding associated with the affected properties. The historical flood records from WDC, information provided by ScW, and other available evidence sources were used alongside the SEPA flood maps to build confidence in hotspot identification and to improve understanding of the underlying flood mechanisms. During the initial assessment, hotspots were ranked according to the scale of potential impact, with locations containing the greatest number of properties at risk receiving the highest priority, these were then agreed with WDC. The hotspots identified for Clydebank are presented in Figure 3-2 and Table 3-2.
Page 12
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 12 AtkinsRéalis - Baseline / Référence Figure 3-2 - Map showing flood 'hotspot' areas Rank Hotspot Name Council Ward / Within PVA Action Areas 1 Second Avenue / Ramsay Street Clydebank Central / Yes 2 Western Isles Road Clydebank Waterfront / No 3 Duntocher Road Clydebank Central / Yes - partial 4 Livingstone Street Clydebank Central / Yes - partial 5 Melbourne Avenue Clydebank Central / No 6 Low Crescent Clydebank Waterfront / No 7 Dumbarton Road Clydebank Waterfront / Yes 8 Dunedin Terrace Clydebank Waterfront / Yes 9 Kilbowie Road Clydebank Central / Yes 10 Station Road Clydebank Waterfront / No 11 Dumbarton Road (west) Dumbarton / No Table 3-2 - List of Hotspots and the Council Ward they are located within Following publication of the updated 2025 SEPA Flood Maps, the hotspot assessment was reviewed as part of this updated SWMP submission. The revised mapping resulted in changes to the extent and severity of surface water flood risk at a number of locations, and consequently some hotspots identified during the initial assessment no longer met the original screening criteria. The implications of the 2025 SEPA Flood Maps are described in Section 4.2, Root Cause Analysis: Desktop.
Page 13
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 13 AtkinsRéalis - Baseline / Référence 3.1.4 Hotspot Delineation (Step 4) 3.1.4.1 Natural Watersheds When the capacity of the engineered drainage system is exceeded, surface water runoff is unable to enter the drainage network and remains on the ground surface. The runoff therefore follows natural overland flow pathways governed by local topography. In urban areas, surface water will typically convey along road corridors and kerb lines, whereas in rural areas it generally follows natural drainage routes and topographic gradients before accumulating in low-lying areas or local depressions. Where significant volumes of runoff accumulate, this can result in pluvial flooding. To better understand the natural drainage characteristics of the catchment, watershed boundaries were delineated upstream of each hotspot using a Digital Terrain Model (DTM). This analysis was undertaken to identify contributing catchment areas and determine the natural overland flow paths that could influence flooding at each location. The DTM was derived from LiDAR data obtained through the National LiDAR Programme and has a maximum spatial resolution of 0.5 m, providing a high level of detail for assessing local topographic controls on surface water flow. Figure 3-3 provides a map showing the natural (or overland) catchments for each hotspot. Figure 3-3 - Map showing natural watershed boundaries for each hotspot 3.1.4.2 Engineered Systems The ScW sewer model incorporates subcatchment boundaries that have been delineated based on the areas expected to drain to the sewer network. This approach represents the engineered urban drainage system, whereby surface runoff is conveyed to road gullies and roof drainage systems before entering the below-ground sewer network. Once within the network, flows are routed through a series of pipes and associated infrastructure towards treatment facilities or, in the case of storm systems, designated outfalls.
Page 14
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 14 AtkinsRéalis - Baseline / Référence Under typical conditions, the drainage system is designed to accommodate more frequent rainfall events, with road gullies generally intended to intercept runoff up to approximately the 1 in 5-year return period event. As a result, the volume of water entering the sewer network is constrained by both gully capacity and the hydraulic capacity of the sewer system itself. During more extreme rainfall events, runoff can exceed the capacity of the engineered drainage network, preventing flows from entering the system. When this occurs, excess surface water remains above ground and follows natural overland flow routes governed by local topography, potentially resulting in exceedance flows, flow ponding and pluvial flooding. Figure 3-4 provides a map showing the engineered (or below ground sewers) catchments for each hotspot.It should be noted that the hotspots “Station Road” and “Dunbarton Road (west) are not covered by the sewer model, and therefore not considered to contribute engineered flows to the sewer network. Figure 3-4 - Map showing the engineered catchment for each hotspot 3.1.5 Hotspot Interactions Interactions between the hotspots were assessed to determine how runoff and potential solutions in one location may influence the hydraulics of another. For example, Duntocher Road is in the upstream extents of the catchment, and so surface water removed from the system at that point may influence Second Avenue further downstream, with the hydraulic benefit accumulating increasingly further downstream. Figure 3-5 shows a simplified schematic of hotspot interactions in the catchment. As solutions have also been accounted for on the surface water sewer system, watercourses may subsequently benefit from the attenuation of retrofitted SuDS. More complex interactions between the systems may occur which have not been captured, such as overflows between the foul / combined system and storm systems, in addition to bifurcations.
Page 15
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 15 AtkinsRéalis - Baseline / Référence Figure 3-5 – Schematic of the hydraulic linkages between the hotspots within the Clydebank area
Page 16
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 16 AtkinsRéalis - Baseline / Référence 4. Improved Understanding of Flood Risk 4.1 Root Cause Analysis Summary Analysis is required to identify the root causes of flooding at each hotspot, as this provides the evidence base for determining whether intervention is needed and, if so, the most appropriate actions to pursue. Without a clear understanding of the root causes, there is a risk that solutions may be progressed which do not maximise the potential hydraulic benefits or effectively reduce flood risk. To identify effective flood mitigation options, it is important to understand: • The source of flooding – i.e. surface water, sewer flooding, river flooding, groundwater flooding, or a combination of flood mechanisms. • The pathway taken by flood waters from source to receptor. • The location of receptors where flooding occurs and water ultimately ponds or accumulates. An initial root cause analysis was undertaken for the eleven flood hotspots identified across Clydebank using the best available information at the time, including historic flood records, SEPA Flood Maps and ScW sewer model outputs. Since completion of the original assessment, SEPA has published updated Flood Maps (2025), incorporating enhanced datasets and modelling methodologies. These updates indicate changes in predicted flood risk at a number of locations and have been taken into account during this review. Following submission of the first iteration of the Clydebank SWMP in April 2024, a workshop was held in December 2025 involving WDC, ScW, Scottish Canals and Network Rail. The workshop explored opportunities to align flood risk management interventions with existing and planned investment programmes across the catchment. Discussions highlighted the interconnected nature of surface water, sewerage, railway drainage, watercourse and canal systems, reinforcing the importance of continued collaboration to develop sustainable, catchment-wide solutions. Particular focus was placed on flooding affecting Clydebank Station, opportunities associated with the Forth and Clyde Canal, and ongoing ScW investigations, including the Dalmuir System Plan, through which ScW is seeking to better understand local authority priorities and identify potential opportunities for coordinated investment. The hotspot assessments presented in the following sections have been updated to reflect the outcomes of the December 2025 workshop, the publication of the 2025 SEPA Flood Maps, and subsequent engagement with ScW regarding ongoing investigations within the catchment. The review comprised two stages: an initial desktop assessment of available evidence, followed by a modelling-based appraisal using sewer, pluvial and integrated hydraulic modelling outputs. It should be noted that the hydraulic modelling was completed prior to the December 2025 workshop and publication of the 2025 SEPA Flood Maps. Consequently, the modelling results have been interpreted alongside more recent information, including updated flood mapping, emerging findings from ongoing investigations, and an improved understanding of interactions across the drainage network. In some locations, this newer evidence suggests that elements of the original modelling assessment may need to be revisited as the outcomes of current ScW investigations become available. The updated analysis therefore draws on both the original study findings and the latest understanding of flood risk across the catchment. The initial areas at greatest risk (‘flood hotspot’) were identified and are summarised in Table 4-1. Table 4-1 - Hotspot summary Hotspot Number Hotspot Name Flooding Mechanism Historic Flooding Reported Flooding Impact Data Gaps 1 Second Avenue / Ramsay Street Surface water / sewer Yes (LA and ScW) Building / road
Page 17
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 17 AtkinsRéalis - Baseline / Référence 2 Western Isles Road Surface water / sewer Yes (LA) Building / road 3 Duntocher Road Surface water / sewer / potential fluvial (unnamed watercourse north of Duntocher Road) Yes (LA and ScW) Road Unnamed watercourse and its interaction with storm system upstream not represented in ScW model 4 Livingstone Street Surface water / sewer / potential fluvial (unnamed watercourse travelling west past Drumry Station) Yes (LA and ScW) Building / road Unnamed watercourse data is missing from existing ScW model. 5 Melbourne Avenue Surface water / sewer Yes (LA) Building / road 6 Low Crescent Surface water / sewer / fluvial Yes (LA and ScW) Building / road 7 Dumbarton Road Surface water / sewer / fluvial and potential tidal influence No Building / road 7 Dunedin Terrace Surface water / sewer No Building / road 9 Kilbowie Road Surface water / sewer No (noted ScW reported flooding north of the hotspot) Building / road 10 Station Road Surface water Yes (LA) Road Road drainage 11 Dumbarton Road (west) Surface water Yes (LA) Road Road drainage
Page 18
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 18 AtkinsRéalis - Baseline / Référence 4.2 Root Cause Analysis: Desktop 4.2.1 Second Avenue / Ramsey Street An initial review of the SEPA surface water flood maps identified a number of residential properties within the medium-risk surface water flooding extent (0.5% AEP; 200-year return period). However, the updated SEPA national flood maps published in 2025 indicate a marginal reduction in the extent of predicted surface water flood risk in this area compared to the previous mapping. Despite this, the area around Second Avenue continues to be identified as a local flooding hotspot due to the recorded history of flooding and known drainage constraints. Historic flooding information provided by WDC indicates that the area has experienced flooding during previous severe rainfall events. Records show that a flash flooding incident occurred at Second Avenue on 9 June 2018, attributed to pluvial flooding associated with a blockage or restriction within the drainage system. WDC records also identify a flooding incident at Queen Elizabeth Gardens/Court during the same event, where flooding was attributed to a combination of pluvial runoff and sewer flooding. These records demonstrate a history of surface water and drainage-related flooding within the local area and provide supporting evidence of flood susceptibility, irrespective of the differences between the previous and updated SEPA flood mapping datasets. Second Avenue is recorded on ScW’s external flood register and has also been reported as an internal flooding incident. ScW believes that an uncharted sewer may be present in this location, potentially associated with the historic Boquhanran Burn. ScW has confirmed that further investigations are being undertaken, including additional surveys, to better understand the cause of flooding and the configuration of the local drainage network. Figure 4-1 - Past flooding photos from local residents Figure 4-2 – SEPA Flood Risk Map Comparison (200-year RP) and Flow Path Analysis (Scalgo) 2025 SEPA Flood Maps 2023 SEPA Flood Maps
Page 19
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 19 AtkinsRéalis - Baseline / Référence 4.2.2 Western Isles Road An initial review of the SEPA surface water flood maps identified a number of residential properties within the medium-risk surface water flooding extent (0.5% AEP; 200-year return period). However, the updated SEPA national flood maps published in 2025 indicate a reduced extent of predicted surface water flooding in this area, with fewer properties identified as being at risk compared to the previous mapping. Despite this reduction, the area remains a recognised local flooding hotspot due to the history of flooding incidents and known drainage network constraints. Historic flooding information provided by WDC identifies flooding at Durban Avenue during a rainfall event on 29 January 2020. The recorded source of flooding was attributed to the sewer network, with reports of sewer surcharging at the location. The incident was reported to ScW by a resident, indicating ongoing drainage and sewer capacity issues within the local area. These records provide evidence of historical flooding associated with the drainage network and support the continued designation of the area as being susceptible to flood risk, notwithstanding the reduced extent of flooding shown within the updated SEPA mapping. Durban Avenue is recorded on ScW external flood register and has been subject to previous investigations relating to sewer flooding. Figure 4-3 – SEPA Flood Risk Map Comparison (200-year RP) and Flow Path Analysis (Scalgo) 4.2.3 Duntocher Road An initial review of the SEPA surface water flood maps identified substantial surface water flood risk along Duntocher Road within the medium-risk surface water flooding extent (0.5% AEP; 200-year return period). The updated SEPA national flood maps published in 2025 show broadly similar patterns of flood risk, with only minor changes to the mapped flood extents. While no residential properties are shown to be directly affected, primarily due to housing being set back from the road corridor, Duntocher Road continues to be identified as an area susceptible to surface water flooding. Historic flooding information provided by WDC confirms a history of flooding at this location. Records describe flash flooding at the low point on Duntocher Road, flooding associated with blocked road gullies, and overtopping of an unnamed watercourse running adjacent to the road during heavy rainfall events. Flooding has previously resulted in road closures, with raised manhole covers reported during the June 2018 event. WDC records from both 2016 and 2018 indicate that flooding was related to a combination of intense rainfall, drainage exceedance, blocked gullies and overtopping of the adjacent watercourse, highlighting the interaction between the road drainage system and local watercourses. 2025 SEPA Flood Maps 2023 SEPA Flood Maps
Page 20
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 20 AtkinsRéalis - Baseline / Référence It should be noted that two storm pipes represented within the drainage model discharge to the adjacent park area and convey runoff from the residential catchment to the north. Furthermore, the unnamed burn referred to within the WDC flooding records, which appears to run parallel to Duntocher Road, is not represented within the model. SEPA mapping also identifies a spring to the north-east of the area. The connectivity between the storm drainage system, the small burn/drain and the wider sewer network is currently uncertain and should be investigated as part of any future detailed study to ensure the flooding mechanism is fully understood. ScW has indicated that the burn may connect to the combined sewer network, which could have implications for flood routing and sewer exceedance during storm events. Figure 4-4 – SEPA Flood Risk Map Comparison (200-year RP) and Flow Path Analysis (Scalgo) 4.2.4 Livingstone Street An initial review of the SEPA surface water flood maps identified a number of residential properties at risk of surface water flooding within the Livingstone Street/Linnvale area, with Livingstone Street representing the area of greatest susceptibility. However, the updated SEPA national flood maps published in 2025 indicate a substantially reduced extent of surface water flood risk compared to the previous mapping. Consequently, while flood risk remains present, the number of properties now shown to be affected is significantly lower and would no longer meet the previous hotspot screening criterion of six residential properties being at risk. Despite this reduction in mapped risk, the area remains of interest due to its history of flooding and the potential consequences of disruption to local access routes. Historic flooding information provided by WDC identifies flooding at Livingstone Street during the June 2018 rainfall event. Records indicate that flooding was associated with surface water runoff from the Cripps Avenue area, combined with drainage restrictions and blocked gullies within the local network. WDC records describe runoff flowing towards Livingstone Street and contributing to localised flooding during intense rainfall. These records are supported by reports from previous flood events which highlight the strategic importance of the location, noting that flooding can render Livingstone Street impassable. As the road provides the sole vehicular access route into Linnvale, flooding has the potential to affect residents, local businesses and emergency service access. The Linnvale area, which encompasses the Livingstone Street location, has also been identified by ScW as a High Impact location. ScW has confirmed that they are leading investigations to better understand the causes of flooding in this area. Initial findings suggest that a historic burn located to the north of the railway may be connected to the combined sewer network at Drumry Station, potentially contributing additional flows to an already constrained system during rainfall events. The outcome of these investigations will be important in refining the understanding of local flooding mechanisms and identifying appropriate long-term solutions. Despite the reduced extent of flooding shown on the updated SEPA mapping, the recorded history of flooding, the critical access function of Livingstone Street and the ongoing investigations by ScW indicate that flood risk remains an important consideration within the area. 2025 SEPA Flood Maps 2023 SEPA Flood Maps
Page 21
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 21 AtkinsRéalis - Baseline / Référence Figure 4-5 – SEPA Flood Risk Map Comparison (200-year RP) and Flow Path Analysis (Scalgo) 4.2.5 Melbourne Avenue An initial review of the SEPA surface water flood maps identified surface water flood risk along Melbourne Avenue, affecting sections of the road corridor and adjacent residential properties. The updated SEPA national flood maps published in 2025 show broadly similar flood extents, with only minor changes compared to the previous mapping, although noted that a greater extent of Melbourne Avenue carriageway is shown to be at risk. Historic flooding information provided by WDC confirms a history of flooding at Melbourne Avenue associated with both surface water and sewer-related drainage issues. Records from 2015 and 2018 indicate flooding linked to blocked road drainage and gullies, with heavy rainfall resulting in exceedance of the local drainage system. In particular, WDC records identify the old cast-iron vented manhole located outside 55 Melbourne Avenue as a recurring flooding location. During periods of intense rainfall, water is reported to surcharge through the vented manhole cover at the low point of the street, resulting in localised flooding. WDC records also note incidents where road drainage became blocked, contributing to the accumulation of surface water on the carriageway. The historical flooding records indicate that flooding at Melbourne Avenue is primarily driven by local drainage constraints and sewer interactions rather than overland flow from a wider catchment. The recurring nature of incidents associated with the manhole outside 55 Melbourne Avenue suggests an ongoing capacity or surcharge issue within the drainage network. Figure 4-6 – SEPA Flood Risk Map Comparison (200-year RP) and Flow Path Analysis (Scalgo) 2025 SEPA Flood Maps 2023 SEPA Flood Maps 2025 SEPA Flood Maps 2023 SEPA Flood Maps
Page 22
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 22 AtkinsRéalis - Baseline / Référence 4.2.6 Low Crescent An initial review of the SEPA surface water flood maps identified a number of residential properties at risk of flooding within the Low Crescent area. However, the updated SEPA national flood maps published in 2025 indicate a significant reduction in the extent of predicted surface water flooding compared to the previous mapping, with substantially fewer properties now shown to be affected. Notwithstanding this reduction in mapped surface water risk, the location remains of interest due to its documented flooding history and the presence of fluvial flood risk. SEPA mapping continues to identify areas susceptible to fluvial flooding, including during higher- probability events, with potential impacts to residential properties and sections of the local road network. Historic flooding information provided by WDC indicates that flooding at Low Crescent has been attributed to a combination of pluvial and sewer-related mechanisms. Records from the December 2015 event identify a capacity issue within the drainage system, suggesting that flooding results from interactions between surface water runoff and the sewer network during periods of intense rainfall. These records demonstrate that, although the updated SEPA mapping shows a considerably reduced surface water flood extent, local drainage constraints and sewer exceedance influence flood risk at the site. Figure 4-7 – SEPA Flood Risk Map Comparison (200-year RP) and Flow Path Analysis (Scalgo) 4.2.7 Dumbarton Road During the first iteration of the SWMP, SEPA surface water flood mapping identified a significant area of flood risk at this location, with potential impacts to residential and commercial properties, a school and the A814 Dumbarton Road. However, the updated SEPA Flood Maps published in 2025 indicate a substantial reduction in predicted surface water flood risk, with only limited areas of flooding now identified and minimal risk to properties. Based on the previous hotspot screening criterion of six or more residential properties being at risk, this location would no longer qualify as a flood hotspot under the updated mapping. No historic flooding incidents have been identified for this location from records provided by WDC, nor were any relevant flood reports identified through the review of available media sources. The absence of recorded flooding is consistent with the significantly reduced level of risk shown in the updated SEPA mapping. A review of overland flow pathways using Scalgo suggests that the more extensive flooding predicted by the earlier SEPA mapping may have been influenced by limitations within the underlying digital terrain model. The analysis indicates that flow paths are routed along the Duntocher Burn corridor from the north and appear to be obstructed where the watercourse passes beneath the A814 Dumbarton Road. In reality, the burn is conveyed beneath the road via a bridge or culvert structure that is not fully represented within the terrain data. A similar issue occurs further downstream where the Duntocher Burn passes beneath the Forth and Clyde Canal. These crossings can create "false blockages" within terrain models, resulting in artificial ponding and exaggerated flood extents. Observations from the site visit support this interpretation and are consistent with the notable reduction in flood risk shown by the updated 2025 SEPA Flood Maps. 2025 SEPA Flood Maps 2023 SEPA Flood Maps
Page 23
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 23 AtkinsRéalis - Baseline / Référence Figure 4-8 illustrates the flood risk identified by the SEPA surface water flood maps used during the initial iteration of the study, with a comparison revised flood extents presented within the 2025 SEPA Flood Maps. The comparison demonstrates the significant reduction in predicted risk and supports the conclusion that this location is no longer considered a priority hotspot based on the current mapping evidence. Figure 4-8 – SEPA Flood Risk Map Comparison (200-year RP) and Flow Path Analysis (Scalgo) 4.2.8 Dunedin Terrace An initial review of the SEPA surface water flood maps identified several residential properties at risk of flooding within the medium-risk surface water flooding extent (0.5% AEP; 200-year return period). However, the updated SEPA Flood Maps published in 2025 indicate a notable reduction in the extent of predicted surface water flooding at this location, with fewer properties shown to be affected and only limited areas of flooding depth exceeding 0.3 m. As a result, the location would not necessarily meet the previous hotspot screening criterion of six or more residential properties being at risk and may not have been classified as a flood hotspot based on the updated mapping. No historic flooding incidents have been identified for this location from records provided by WDC, and no relevant flooding reports were identified through the review of available media sources. The absence of recorded flooding is consistent with the reduced level of risk indicated by the updated SEPA surface water flood maps. While some residual surface water flood risk remains evident within the updated mapping, the reduction in both the extent and severity of predicted flooding suggests that the location is less vulnerable than previously indicated. Consequently, although the area should continue to be considered within any wider catchment-scale assessment, the available evidence does not currently support its identification as a priority flood hotspot. 2025 SEPA Flood Maps 2023 SEPA Flood Maps
Page 24
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 24 AtkinsRéalis - Baseline / Référence Figure 4-9 – SEPA Flood Risk Map Comparison (200-year RP) and Flow Path Analysis (Scalgo) 4.2.9 Kilbowie Road An initial review of the SEPA surface water flood maps identified substantial surface water flood risk in the vicinity of Clyde Shopping Centre, with a number of surrounding commercial and residential properties shown to be susceptible to flooding within the medium-risk surface water flooding extent (0.5% AEP; 200-year return period). The updated SEPA Flood Maps published in 2025 indicate a modest reduction in the extent of predicted flooding compared to the previous dataset. However, significant areas of surface water flood risk remain, and the location continues to be identified as an area of notable flood susceptibility within the catchment. No historic flooding incidents have been identified for this location from records provided by WDC. However, ScW has identified a location on its flood register at Cambridge Avenue, immediately to the north of the hotspot, indicating a history of drainage and sewer-related flooding issues within the wider area. The proximity of this recorded flooding location suggests that local drainage constraints may influence flood risk in the vicinity of the shopping centre. Although no flooding records have been identified from WDC, media reports provide evidence of flooding within the area. In August 2021, reports described flooding on Kilbowie Road near Clyde Shopping Centre, with sections of the road reported to be underwater following heavy rainfall. The incident required attendance by emergency services, with fire crews rescuing a vehicle from a deep flooded area adjacent to the shopping centre. These reports demonstrate that significant surface water accumulation can occur locally during intense rainfall events, affecting both road users and access through the area. 2025 SEPA Flood Maps 2023 SEPA Flood Maps 2025 SEPA Flood Maps 2023 SEPA Flood Maps
Page 25
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 25 AtkinsRéalis - Baseline / Référence Figure 4-10 – SEPA Flood Risk Map Comparison and Flow Path Analysis (Scalgo) 4.2.10 Station Road An initial review of the SEPA surface water flood maps identified substantial surface water flood risk at the low point on Station Road, with flooding largely confined to the road corridor and adjacent low-lying areas. The updated SEPA Flood Maps published in 2025 show broadly similar flood extents and depths to the previous dataset, indicating that there has been little change in the understanding of flood risk at this location. Station Road therefore continues to be identified as an area susceptible to flooding, particularly during intense rainfall events. Historic flooding information provided by WDC confirms a history of flooding at this location. Records from December 2015 describe deep flooding at the low point on Station Road associated with a combination of pluvial and fluvial flooding, including overtopping of an unnamed burn. Subsequent flooding during February 2020 was attributed to debris and runoff from adjacent agricultural land, which blocked road gullies and reduced the effectiveness of the highway drainage system. Both incidents resulted in road closures, highlighting the susceptibility of Station Road to flooding from multiple sources and the importance of maintaining drainage infrastructure. The WDC records indicate that flooding at Station Road is influenced by a combination of overland runoff, interactions with the adjacent watercourse and blockages within the road drainage network. The contribution of runoff from neighbouring agricultural land suggests that catchment processes outside the urban area also play a role in flood generation at this location. The upstream natural watershed is large and is likely to play a key role in terms of rural runoff reaching this site. During subsequent engagement, WDC highlighted that flooding at Station Road can have a disproportionately large impact on the surrounding area despite the limited number of properties directly affected. Flooding at the low point can lead to drivers attempting to pass through deep water, creating a safety risk, whilst closures of the road can affect access to nearby businesses and disrupt the slip road connection to the A82. As a result, the significance of this location is linked not only to the flood hazard itself but also to the wider transport and access implications associated with flooding events. Social media reports of previous flood events provide further evidence of the site's susceptibility to flooding, with Station Road reported to have been closed on several occasions due to floodwater. These reports are consistent with the historical records held by WDC and reinforce the importance of the route as a potential point of disruption during severe weather events.
Page 26
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 26 AtkinsRéalis - Baseline / Référence Figure 4-11 – SEPA Flood Risk Map Comparison and Flow Path Analysis (Scalgo) 4.3 Root Cause Analysis: Modelling Different stakeholder requirements generate a need for different types of models, varying from small, localized studies, to large strategic catchment wide studies. Models can include representation of foul/combined sewer networks, storm sewer systems, watercourses, overland flow pathways, and/or all these elements integrated together. For a SWMP, how runoff is represented in the model is key. Runoff modelling defines how much of the rainfall falling on a catchment becomes runoff and how quickly this enters the drainage system, should capacity allow. For this study, to build a clearer understanding of root causes of flooding within Clydebank, the model assessment was broken down into three phases: 1D sewer network modelling: the sewer network model, as received from ScW, representing predicted out-of-sewer flooding. Subcatchments are directed to specific manholes so as there is no surface, where flow runoff is directed if it cannot enter the system is not modelled. 2D pluvial modelling: representing flows over the surface, with gully losses represented. No interaction with the sewer network. 1D – 2D integrated modelling: the sewer network, with rainfall applied to the mesh and gullies. Represents the combined impact of pluvial and out-of-sewer flooding/sewer capacity constraints, for a more accurate representation of the true extent of flooding. 4.3.1 1D Sewer Network Modelling The 1D hydraulic model obtained by ScW to cover the hotspots in the Clydebank area was DOA000333 Dalmuir Current v24, which was last committed on 18/11/2024, base scenario. This was used to obtain an understanding of the predicted sewer performance and flooding within the hotspots. Water companies typically use InfoWorks models to represent the below ground (engineered) system. Prediction of flow within pipes is based on runoff from predefined surface areas draining to “nodes” (which are typically manholes). Calculations are made at each node, determining flow arriving, continuing downstream, and water 2025 SEPA Flood Maps 2023 SEPA Flood Maps
Page 27
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 27 AtkinsRéalis - Baseline / Référence levels in the nodes. Flood volumes and depths is predicted at ground level, giving the user an estimation of flooding likely to occur at each node – giving an idea of what might be impacted by flood water nearby. In 1D models, predefined surface areas are set in subcatchments. Subcatchments make up the total catchment of a drainage network but serve to add detail on where water will enter the drainage system on a local level. Each subcatchment calculates runoff in response to rainfall depending based on the proportion of runoff surfaces applied. In other words, the speed and volume of runoff is dependent on how much impermeable (roads and roofs) or permeable (gardens / soils) the subcatchment covers. Highly impermeable subcatchments generate faster responses with less infiltration losses, while highly permeable subcatchments generate slower responses with more infiltration losses. Figure 4-12 shows a subcatchment in a 1D hydraulic urban drainage model. The green boundary indicates what area the subcatchment is draining (roofs, road, and some garden space), and the green arrow indicates where it’s draining to. The red lines are pipes, and red dots are manholes (or nodes). The figure demonstrates how subcatchments cover the total catchment area, like a jigsaw puzzle. Figure 4-12 - 1D hydraulic model visual representation These models are useful for wastewater studies, whereby the performance of the piped system is the primary focus of assessment. Water companies invest to build these models and undertake flow verification to ensure high confidence in flow predictions in their underground network (for which they are responsible). However, a fundamental limitation of 1D drainage models is they assume runoff either enters the engineered piped system directly or is lost it (i.e. it never reaches the system) – which can happen for a whole manner of reasons (e.g. such as capacity of gullies, pooling on the surface, walls blocking flow paths). For this reason, 1D models are not appropriate for assessing pluvial flooding and flow paths, as per required for a SWMP. While the primary goal of the SWMP is to address surface water flooding, it is important to understand where sewer flooding is likely to occur and consider how this may impact surface water solutions. Simulations were run for the existing 1D models for 1 in 30-year return period event and 1 in 200-year return period event and outlined in the following section. The following section provides a summary of the predicted flooding from the piped network for the high priority hotspots within Clydebank.
Page 28
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 28 AtkinsRéalis - Baseline / Référence
Page 29
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 29 AtkinsRéalis - Baseline / Référence 4.3.1.1 Second Avenue / Ramsay Street In the 1 in 30-year return period event, the sewer network conveys flows towards the topographic low point within the hotspot, where approximately 1,500m³ of out-of-sewer flooding is predicted from combined manhole NS48718301. This represents significant sewer flooding and indicates that the existing sewer network is unable to contain and convey flows during the event. The volume of flooding predicted from a single manhole suggests that sewer network exceedance is a primary flooding mechanism at this location and reflects a significant capacity constraint within the combined sewer system. Figure 4-13 illustrates predicted flooding from the 1D model. Figure 4-13 - Map of flooded nodes in the 1D hydraulic model during the 30-year 60 minute event
Page 30
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 30 AtkinsRéalis - Baseline / Référence 4.3.1.2 Western Isles Road Several combined sewer manholes along Durban Avenue are predicted to surcharge during the 1 in 30-year return period event (refer to Figure 4-14). Manhole NS47716601 is predicted to experience the greatest flood volume, at approximately 151 m³. This represents a significant volume of out-of-sewer flooding and indicates that the local combined sewer network is unable to contain and convey flows during the event. The modelling therefore suggests that sewer network exceedance is a primary contributor to flooding at this location, highlighting capacity constraints within the existing drainage system. Figure 4-14 - Map of flooded nodes in the 1D hydraulic model during the 30-year 60 minute event
Page 31
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 31 AtkinsRéalis - Baseline / Référence 4.3.1.3 Duntocher Road The 1D modelling indicates that four combined sewer manholes are predicted to surcharge by more than 100 m³ during the 1 in 30-year return period event, with NS49726001 and NS49725003 each predicted to flood by more than 500 m³ (Figure 4-15). These manholes are located within, or immediately upstream of, the low point on Duntocher Road and collectively represent a substantial volume of out-of-sewer flooding. The modelling indicates that the combined sewer network is unable to contain and convey flows during the event, resulting in significant sewer flooding at this location. The magnitude of the predicted flood volumes suggests that sewer network exceedance is a primary flooding mechanism at Duntocher Road and highlights a significant capacity constraint within the existing drainage system. However, these results should be considered alongside the limitations identified in the desktop root cause analysis. In particular, the unnamed watercourse referenced within the WDC flood records is not represented within the hydraulic model, despite evidence that it may interact with the combined sewer network. ScW is currently investigating the potential connectivity between this watercourse, the sewer system and the wider drainage network. In addition, the interaction between the storm drainage outfalls, adjacent parkland and the unnamed watercourse remains uncertain. Consequently, whilst the modelling indicates that sewer flooding is a significant contributor to flood risk at this location, the results should be treated with caution pending the outcome of the ongoing ScW investigations and any subsequent refinement of the flooding mechanisms. Figure 4-15 - Map of flooded nodes in the 1D hydraulic model during the 30-year 60 minute event
Page 32
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 32 AtkinsRéalis - Baseline / Référence 4.3.1.4 Livingstone Street Several combined sewer manholes along Livingstone Street are predicted to surcharge during the 1 in 30-year return period event (refer to Figure 4-16). In particular, manholes NS50706301 and NS50705302 are predicted to flood by approximately 110 m³ and 187 m³ respectively. These represent significant volumes of out-of-sewer flooding and indicate that the local combined sewer network is unable to contain and convey flows during the event. The modelling therefore suggests that sewer network exceedance is a primary contributor to flooding within the Livingstone Street area, highlighting capacity constraints within the existing drainage system. However, the limitations and uncertainties identified within the desktop root cause analysis should be taken into account when interpreting these results. In particular, the ongoing ScW investigations into the potential interaction between historic drainage features and the combined sewer network may provide additional information regarding the flooding mechanisms operating within the area. Consequently, the model results should be treated with a degree of caution pending the outcome of these investigations and any subsequent updates to the understanding of flood risk at this location. Figure 4-16 - Map of flooded nodes in the 1D hydraulic model during the 30-year 60 minute event
Page 33
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 33 AtkinsRéalis - Baseline / Référence 4.3.1.5 Melbourne Avenue Several sewer manholes along Melbourne Avenue are predicted to surcharge during the 1 in 30-year return period event. Manhole NS47728501 has the highest predicted flood volume at approximately 345 m³, whilst NS47728502 and NS47727402 are predicted to flood by approximately 135 m³ and 62 m³ respectively. These represent significant volumes of out-of-sewer flooding and indicate that the local combined sewer network is unable to contain and convey flows during the event. The resulting exceedance flows would discharge onto the surface and follow the road gradient towards the low point on Melbourne Avenue, contributing to flooding within the hotspot. The modelling therefore suggests that sewer network exceedance is a significant contributor to flooding at this location and highlights local capacity constraints within the drainage system. The model results are consistent with the historical flood information provided by WDC, which identifies recurring flooding associated with surcharge from the vented manhole outside 55 Melbourne Avenue, as well as incidents linked to blocked road gullies and drainage infrastructure. These records support the conclusion that both sewer capacity limitations and local drainage constraints influence flood risk within the area. Figure 4-17 - Map of flooded nodes in the 1D hydraulic model during the 30-year 60 minute event
Page 34
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 34 AtkinsRéalis - Baseline / Référence 4.3.1.6 Low Crescent Numerous combined sewer manholes within the Low Crescent hotspot are predicted to surcharge during both the 1 in 30-year RP event. The predicted out-of-sewer flood volumes are substantial, with the largest flood volumes occurring at NS50696702 (564m³), NS50697802 (234m³), NS50695803 (199m³) and NS51690601 (192m³) (Figure 4-18). These results indicate that the combined sewer network is unable to contain and convey flows during storm events, resulting in significant sewer flooding within the hotspot. The magnitude and distribution of the predicted flood volumes suggest that sewer network exceedance is a significant contributor to the overall flooding mechanism and highlight capacity constraints within the existing drainage system. The desktop assessment also identified that flood risk within the area is influenced by a combination of surface water and fluvial processes, with the updated SEPA Flood Maps continuing to indicate areas of fluvial flood risk. Figure 4-18 - Map of flooded nodes in the 1D hydraulic model during the 30-year 60 minute event
Page 35
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 35 AtkinsRéalis - Baseline / Référence 4.3.1.7 Dumbarton Road Several combined sewer manholes along Dumbarton Road and Swindon Street are predicted to surcharge during the 1 in 30-year return period event (refer to Figure 4-19). In particular, manholes NS48712201 and NS48713303 are predicted to flood by approximately 133 m³ and 184 m³ respectively. These represent significant volumes of out-of-sewer flooding and indicate that the local combined sewer network is unable to contain and convey flows during the event. The modelling therefore suggests that sewer network exceedance is a significant source of flooding within the area and highlights local capacity constraints within the existing drainage system. Figure 4-19 - Map of flooded nodes in the 1D hydraulic model during the 30-year 60 minute event
Page 36
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 36 AtkinsRéalis - Baseline / Référence 4.3.1.8 Dunedin Terrace Several combined sewer manholes along Dunedin Terrace and North Douglas Street are predicted to surcharge during the 1 in 30-year return period event (refer to Figure 4-20). The predicted out-of-sewer flood volumes are generally less than 100 m³, indicating a comparatively lower level of sewer flooding than at a number of the other assessed hotspots. Nevertheless, the results demonstrate that the local combined sewer network is unable to fully contain and convey flows during the event, resulting in localised sewer exceedance within the area. Figure 4-20 - Map of flooded nodes in the 1D hydraulic model during the 30-year 60 minute event
Page 37
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 37 AtkinsRéalis - Baseline / Référence 4.3.1.9 Kilbowie Road Sewer flooding is predicted at the junction of Kilbowie Road and Second Avenue, with approximately 250 m³ of out-of-sewer flooding predicted during the 1 in 30-year return period event. Once discharged from the sewer network, these flows are likely to be conveyed along the road corridor towards lower ground on Kilbowie Road. The modelling therefore indicates that sewer network exceedance is a significant contributor to flooding within this hotspot and reflects capacity constraints within the local combined sewer system. Figure 4-21 - Map of flooded nodes in the 1D hydraulic model during the 30-year 60 minute event 4.3.1.10 Station Road The Station Road hotspot was not covered by the 1D sewer model, therefore, predicted out of sewer flooding could not be analysed. 4.3.1.11 Dumbarton Road (west) The Dumbarton Road (west) hotspot was not covered by the 1D sewer model, therefore, predicted out of sewer flooding could not be analysed.
Page 38
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 38 AtkinsRéalis - Baseline / Référence 4.3.2 Pluvial Only Flood Modelling A 2D pluvial model was developed to understand overland flow routes within the catchment when rainfall was directly applied to the model surface (also known as a rainfall-to-mesh model). Scottish Publicly Available LiDAR data5 of 0.5m resolution was used to create a Digital Terrain Model (DTM), to represent the topography of the study area. Mastermap GIS data was imported into the model to explicitly represent building and roads, which can influence flow paths by obstructing of channelling water. These modifications replicate the impact of raised and dropped kerbs, which can influence the direction and destination of water on the surface. Buildings with a considerable roof area (>10 m2) were modelled with 10% porosity to replicate the impact of water moving through the property, either through ventilation in a building’s foundation or through the property itself once the threshold is breached. Buildings with roof area <10 m2 (e.g. garden sheds) were modelled simplistically as 200 mm stubs. This model was set up to represent how the sewer network “should-be”. In other words, in optimal condition (e.g. no blockages, sediment), and capable of coping with a 30-year return period storm event. This means that outputs from this model highlight what surface water flooding would remain if the existing drainage system was working optimally. The following sections summarise the findings of this assessment, illustrating the predicted extents when only pluvial flooding is considered. It should be noted that depths below 150mm have been filtered out, so that depths that would be considered to cause disruption to infrastructure and property flooding are visualised. 4.3.2.1 Second Avenue / Ramsay Street When the sewer network is not considered, there is still significant flooding that can be attributed to pluvial causes at this hotspot, with properties impacted with likely internal flooding, and significant depths predicted in the road. Most of the surface water flooding predicted at Second Avenue / Ramsay Street is because of overland flow paths. The residential streets Park Road and Duntocher Road are key surface water conveyance paths into the hotspot. Park Road has a relatively steep fall directly to the low point of the hotspot, which lies between St Stephens Church and St Stephens Primary School. Therefore, most of the surface water routes towards this area where the drainage system in place is not effective enough to drain it and/or convey it downstream. Therefore, surface water spreads out overland. 5Scottish Remote Sensing Portal. Available at: https://remotesensingdata.gov.scot/data#/map
Page 39
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 39 AtkinsRéalis - Baseline / Référence Figure 4-22 - Predicted pluvial only flood extents at the 1 in 30-year return period event 4.3.2.2 Western Isles Road Most of the surface water flooding experienced at the Western Isles Road hotspot is due to overland flow paths. Western Isles Road, Delhi Avenue and Durban Avenue are key surface water conveyance paths. Western Isles Road falls the most steeply towards the hotspot and has the highest flow contribution. The model predicts that most pluvial flooding is contained within the road for this event, and does not impact properties. Figure 4-23 - Predicted pluvial only flood extents at the 1 in 30-year return period event
Page 40
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 40 AtkinsRéalis - Baseline / Référence 4.3.2.3 Duntocher Road When pluvial flooding is assessed in isolation, the model predicts that the impact is not significant, although does cause disruption to the road. Most of this surface water originates from Briar Drive and Kilbowie Road from the southeast. Additionally, some surface water comes from the high point on Duntocher Road from the west. As noted though, at this hotspot, complex interactions and data gaps mean that the true mechanism of flooding may not be understood. Figure 4-24 - Predicted pluvial only flood extents at the 1 in 30-year return period event
Page 41
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 41 AtkinsRéalis - Baseline / Référence 4.3.2.4 Livingstone Street When considering pluvial flooding in isolation, the modelling predicts limited and localised areas of surface water ponding, primarily within a number of cul-de-sac areas located within the hotspot. The predicted flood extents and depths suggest some disruption to the local road network; however, the flooding is generally contained and does not indicate widespread surface water flood risk. These results are consistent with the updated 2025 SEPA Flood Maps, which show a similarly limited extent of surface water flooding within the area. Figure 4-25 - Predicted pluvial only flood extents at the 1 in 30-year return period event
Page 42
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 42 AtkinsRéalis - Baseline / Référence 4.3.2.5 Melbourne Avenue The pluvial-only modelling indicates that surface water runoff accumulates at the low point on Melbourne Avenue, with the majority of runoff conveyed from higher ground further north along the road. Whilst the predicted flooding is generally localised, model results indicate that flood depths are sufficient to result in impacts to the carriageway and disruption to road users during the design event. This suggests that surface water runoff contributes to flood risk at the location, particularly where flows concentrate at the low point on Melbourne Avenue. Figure 4-26 - Predicted pluvial only flood extents at the 1 in 30-year return period event
Page 43
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 43 AtkinsRéalis - Baseline / Référence 4.3.2.6 Low Crescent The pluvial-only modelling indicates localised surface water ponding at the junction of Abbott Crescent and North Elgin Street, with runoff primarily conveyed from the higher ground around Johnson Avenue before accumulating at the local topographic low point. Additional isolated ponding is also predicted on Sinclair Street. The predicted flooding is generally confined to the road network and surrounding low spots, with depths indicating potential disruption to local access routes during the design event. These results are consistent with the updated 2025 SEPA Flood Maps, which show residual surface water flood risk concentrated around the same low-lying areas rather than widespread flooding across the hotspot. Figure 4-27 - Predicted pluvial only flood extents at the 1 in 30-year return period event
Page 44
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 44 AtkinsRéalis - Baseline / Référence 4.3.2.7 Dumbarton Road The pluvial-only modelling indicates localised surface water ponding on Dumbarton Road in the vicinity of the junction with French Street during the 1 in 30-year return period event. The predicted flooding is largely confined to the road corridor, with depths suggesting some disruption to road users but limited wider impacts. These results are broadly consistent with the updated 2025 SEPA Flood Maps, which indicate a substantially reduced extent of surface water flood risk compared to the previous mapping and support the conclusion that pluvial flood risk at this location is relatively limited. Figure 4-28 - Predicted pluvial only flood extents at the 1 in 30-year return period event
Page 45
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 45 AtkinsRéalis - Baseline / Référence 4.3.2.8 Dunedin Terrace The pluvial-only modelling indicates localised surface water ponding along North Douglas Street and Dunedin Terrace during the 1 in 30-year return period event. The predicted flooding is generally shallow and confined to isolated low points within the road network, with limited potential for wider impacts. These results are consistent with the updated 2025 SEPA Flood Maps, which show a reduced extent of surface water flood risk at this location and support the conclusion that pluvial flooding is relatively limited compared to that indicated by the previous mapping. Figure 4-29 - Predicted pluvial only flood extents at the 1 in 30-year return period event
Page 46
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 46 AtkinsRéalis - Baseline / Référence 4.3.2.9 Kilbowie Road The pluvial-only modelling indicates notable surface water ponding on Coldstream Road during the 1 in 30-year return period event, with runoff conveyed from higher ground to the east. Additional isolated areas of ponding are also predicted within the Clyde Shopping Centre area. The model results indicate flood depths that could result in disruption to the local road network and access routes during intense rainfall events. These findings are broadly consistent with both the previous and updated 2025 SEPA Flood Maps, which continue to identify this location as being susceptible to surface water flooding, albeit with a slightly reduced extent compared to the previous mapping. Figure 4-30 - Predicted pluvial only flood extents at the 1 in 30-year return period event 4.3.2.10 Station Road Due to limitations on the extent of network model, this hotspot was not assessed in the pluvial only model. 4.3.2.11 Dumbarton Road (west) Due to limitations on the extent of network model, this hotspot was not assessed in the pluvial only model.
Page 47
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 47 AtkinsRéalis - Baseline / Référence 4.3.3 Integrated 1D - 2D Runoff Model The 1D sewer network elements from the ScW Dalmuir hydraulic model were integrated with the 2D pluvial model to improve understanding of the interaction between the underground drainage system (e.g. sewers, culverts and manholes) and overland surface water flow pathways. This integrated modelling approach enabled assessment of the exchange of flows between the sewer network and the ground surface during storm events, helping to identify the dominant flood mechanisms within each hotspot. The integrated model output provides a representation of the combined impact of pluvial flooding and sewer exceedance, allowing areas affected by both surface water runoff and surcharging drainage infrastructure to be identified. This supports a more comprehensive understanding of flood risk than consideration of either source in isolation and assists in determining the relative contribution of surface water and sewer network constraints to observed flooding at each location. The following sections summarise the findings of the integrated modelling assessment for each hotspot and compare the predicted flooding mechanisms and extents against the SEPA surface water flood maps. This comparison has been used to identify areas of agreement and discrepancy between the datasets, improve confidence in the understanding of flood risk. Please note that this modelling assessment was undertaken prior to the release of the 2025 SEPA flood maps and the visual comparison is to the previous dataset. 4.3.3.1 Second Avenue / Ramsay Street This hotspot is predicted to flood due to a combination of surface water runoff and sewer exceedance. The integrated 1D-2D model indicates that flooding results from the combined effects of pluvial runoff and surcharging within the sewer network. The predicted flood extents from the integrated modelling align closely with the updated SEPA Flood Maps, providing confidence in the representation of flood risk at this location. Model results show that the principal surface water flow pathways originate from Park Road and Duntocher Road to the north, with runoff conveyed rapidly downslope towards the low point located between St Stephen’s Church and St Stephen’s Primary School. As water accumulates within this topographic depression, the capacity of the local sewer network is exceeded, limiting its ability to accept and convey incoming flows downstream. Consequently, a significant proportion of the runoff remains on the surface, contributing to the observed flood extents. The modelling indicates that sewer flooding is a significant component of the overall flood mechanism, with sewer surcharge contributing to flooding within the area. Evidence gathered during the site visit supports this finding, with the presence of toilet paper around roadside gullies suggesting that sewer surcharge has occurred historically. Model results further demonstrate that both surface water flooding and sewer exceedance occur during the more frequent 1 in 1-year return period event, indicating that drainage system constraints are present even during relatively modest rainfall events.
Page 48
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 48 AtkinsRéalis - Baseline / Référence Figure 4-31 – Integrated model predicted flooding compared to SEPA pluvial flood maps (200 year RP) 4.3.3.2 Western Isles Road The integrated modelling indicates that flooding at the Western Isles Road hotspot is influenced by a combination of overland flow and sewer network exceedance. Surface water runoff is primarily conveyed along Western Isles Road, Delhi Avenue and Durban Avenue, with Western Isles Road contributing the greatest proportion of runoff due to its steeper gradient towards the hotspot. The relatively flat topography within the low-lying area around Durban Avenue limits the ability of surface water to drain effectively, resulting in localised ponding. During the initial SWMP assessment, the integrated modelling predicted a considerably smaller flood extent than that shown by the SEPA surface water flood maps available at the time. However, the updated 2025 SEPA Flood Maps indicate a reduced extent of surface water flood risk and are now much more closely aligned with the integrated model predictions. Both datasets identify flooding concentrated around the low-lying areas of the hotspot, increasing confidence in the current understanding of flood risk at this location. The modelling also indicates that several gullies and combined sewer manholes within and upstream of the hotspot are predicted to surcharge during heavy rainfall events, demonstrating that the combined sewer network is unable to effectively accommodate flows. Consequently, whilst the updated SEPA flood maps continue to identify the location as being susceptible to flooding, the modelling suggests that the flooding mechanism is not solely driven by overland surface water runoff. Instead, sewer network exceedance is considered to be a significant contributor to the observed flooding, with interactions between the surface and below-ground drainage systems influencing the overall flood risk at this location.
Page 49
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 49 AtkinsRéalis - Baseline / Référence Figure 4-32 - Integrated model predicted flooding compared to SEPA pluvial flood maps (200 year RP)
Page 50
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 50 AtkinsRéalis - Baseline / Référence 4.3.3.3 Duntocher Road The integrated modelling indicates that flooding at Duntocher Road is driven by a combination of overland flow and sewer network exceedance. Surface water runoff is conveyed towards the low point on Duntocher Road from Briar Drive and Kilbowie Road to the south-east, together with additional runoff from higher ground to the west along Duntocher Road. During the initial SWMP assessment, the integrated modelling results showed good agreement with the SEPA surface water flood maps available at the time. Following publication of the 2025 SEPA Flood Maps, this agreement remains evident, with the updated mapping continuing to identify Duntocher Road as a significant flood risk location. The close alignment between the integrated modelling outputs, the updated SEPA Flood Maps and historical flooding records provided by WDC provides a high level of confidence in the understanding of flood risk at this location. In particular, the modelling supports historical reports of flooding at the low point on Duntocher Road, including road flooding, disruption to the local road network and flooding associated with the adjacent drainage system. The modelling indicates that sewer exceedance is a significant contributor to the overall flood mechanism, with drainage system capacity constraints resulting in surcharging and surface flooding during relatively frequent rainfall events. This suggests that sewer flooding is a key driver of flood risk at this location, acting in combination with overland runoff conveyed towards the local topographic low point. It should be noted that the unnamed watercourse referred to in the WDC flooding records is not represented within the hydraulic model. As discussed in Section 4.2, ScW considers that this watercourse may connect to the combined sewer network and is currently investigating its connectivity and influence on flooding within the area. Consequently, whilst the available evidence indicates that sewer flooding is a key contributor to flood risk at Duntocher Road, the results should be interpreted with caution and reviewed in light of the findings from the ongoing ScW investigations. Figure 4-33 - Integrated model predicted flooding compared to SEPA pluvial flood maps (200-year RP)
Page 51
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 51 AtkinsRéalis - Baseline / Référence 4.3.3.4 Livingstone Street The integrated modelling indicates that flooding within the Livingstone Street hotspot is influenced by a combination of surface water runoff and sewer network exceedance, with flooding primarily concentrated on Livingstone Street and extending to adjacent roads including Shinwell Avenue and Silkin Avenue. The modelling suggests that the dominant flooding mechanism is sewer exceedance, with several gullies and manholes connected to the combined sewer network predicted to surcharge and discharge flows onto the surface during storm events. As a result, sewer flooding is considered to make a significant contribution to the observed flood extents. During the initial SWMP assessment, the integrated modelling predicted a substantially smaller flood extent than that shown by the SEPA surface water flood maps available at the time. However, the updated 2025 SEPA Flood Maps indicate a significantly reduced extent of surface water flood risk and are now much more closely aligned with the integrated model predictions. This improved agreement between the modelling and the updated SEPA mapping increases confidence that flood risk at Livingstone Street is more localised than previously indicated and that widespread pluvial flooding is unlikely to be the principal driver of flooding within the area. The modelling results are also consistent with the historical flooding records and information provided by ScW, which has identified the Linnvale area as a High Impact location. Together, the available evidence suggests that sewer network performance is a key contributor to flood risk at this location. However, as discussed in the desktop root cause analysis, ScW is currently undertaking investigations into the potential influence of historic watercourses and their interaction with the combined sewer network. Consequently, whilst sewer flooding is currently considered to be the primary flooding mechanism at Livingstone Street, the modelling results should be interpreted with caution and reviewed following completion of the ongoing ScW investigations. Figure 4-34 - Integrated model predicted flooding compared to SEPA pluvial flood maps (200-year RP)
Page 52
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 52 AtkinsRéalis - Baseline / Référence 4.3.3.5 Melbourne Avenue The integrated modelling indicates that flooding at the Melbourne Avenue hotspot is influenced by a combination of surface water runoff and sewer network exceedance. Surface water runoff is conveyed from higher ground to the north along Melbourne Avenue before accumulating at the local topographic low point. The modelling also predicts surcharge from a number of combined sewer manholes and gullies, indicating that sewer flooding contributes significantly to the observed flood extents. The integrated model results are consistent with the historical flooding information provided by WDC, which identifies repeated flooding associated with the vented manhole outside 55 Melbourne Avenue, together with reports of blocked highway drainage and gully infrastructure. This evidence supports the conclusion that flooding at the site is influenced by both local drainage constraints and sewer network performance. The predicted flood extents also show reasonable agreement with both the original and updated 2025 SEPA Flood Maps, which continue to identify Melbourne Avenue as an area susceptible to flooding. Collectively, the model results, flood records and SEPA mapping indicate that flooding is concentrated around the low point on Melbourne Avenue and is driven by the interaction between overland runoff and sewer surcharge. Consequently, the available evidence suggests that sewer network exceedance is a significant contributor to flood risk at this location, with surface water runoff acting to exacerbate flooding once the capacity of the local drainage system is exceeded. However, the results should be interpreted alongside the historical flood evidence and wider understanding of local drainage conditions when considering future mitigation measures. Figure 4-35 - Integrated model predicted flooding compared to SEPA pluvial flood maps (200-year RP)
Page 53
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 53 AtkinsRéalis - Baseline / Référence 4.3.3.6 Low Crescent The integrated modelling indicates that flooding within the Low Crescent hotspot is influenced by a combination of surface water runoff and sewer network exceedance. Flooding is concentrated around local topographic low points, particularly in the vicinity of Abbott Crescent, North Elgin Street and Sinclair Street, with runoff conveyed from higher ground including the Johnson Avenue area before accumulating within the hotspot. During the initial SWMP assessment, the integrated modelling showed a smaller extent of flooding than that indicated by the SEPA surface water flood maps available at the time. However, the updated 2025 SEPA Flood Maps indicate a substantially reduced extent of surface water flood risk and are now more closely aligned with the integrated model predictions. Both datasets suggest that flooding is generally localised and focused around the principal low points within the hotspot rather than being widespread across the wider area. The available evidence indicates that sewer network performance is a significant contributor to flood risk, with sewer capacity constraints likely acting in combination with localised surface water ponding. In addition, the updated SEPA Flood Maps continue to identify areas of fluvial flood risk within and around the hotspot. Whilst the integrated model does not explicitly represent fluvial flooding mechanisms, the mapped fluvial flood extents indicate that flooding within the area may be influenced by interactions between surface water, sewer and fluvial processes. Consequently, whilst the updated SEPA mapping indicates a reduced level of surface water flood risk compared to the previous dataset, the combined evidence from hydraulic modelling, historical flooding records, sewer flooding records and SEPA flood mapping suggests that flood risk at Low Crescent is influenced by the interaction of surface water, sewer and fluvial mechanisms, with sewer flooding remaining a significant contributor to the overall risk. Figure 4-36 - Integrated model predicted flooding compared to SEPA pluvial flood maps (200 year RP)
Page 54
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 54 AtkinsRéalis - Baseline / Référence 4.3.3.7 Dumbarton Road The integrated modelling indicates that flooding on Dumbarton Road is limited and primarily confined to localised areas around the low point near the junction with French Street. The model predicts only shallow flooding in isolated locations, with the majority of runoff conveyed towards the adjacent watercourse. The results suggest that neither pluvial runoff nor sewer network exceedance are significant flood mechanisms at this location and that impacts to properties and infrastructure are likely to be limited. During the initial SWMP assessment, there was a notable disparity between the integrated model results and the SEPA surface water flood maps available at the time, which identified a much greater extent of flood risk affecting surrounding properties, the school and sections of the A814. As discussed in Section 4.2, subsequent review indicated that the original SEPA mapping was likely influenced by limitations within the underlying terrain model. In particular, the Duntocher Burn passes beneath both Dumbarton Road and the Forth and Clyde Canal via culvert and bridge structures that are not fully represented within the digital terrain model. This creates artificial barriers, or "false blockages", within mapped flow paths, resulting in unrealistic ponding and exaggerated surface water flood extents. The release of the 2025 SEPA Flood Maps has significantly reduced the mapped flood risk at this location and is now much more closely aligned with the integrated model predictions. Both datasets indicate that pluvial flood risk is limited and that there is little evidence of significant sewer flooding within the hotspot. Consequently, the available evidence from the updated SEPA mapping, hydraulic modelling and site observations supports the conclusion that flood risk at this location is substantially lower than indicated by the original SEPA dataset and that the previously identified hotspot was largely influenced by terrain-model artefacts associated with the representation of the Duntocher Burn crossings. Figure 4-37 - Integrated model predicted flooding compared to SEPA pluvial flood maps (200 year RP)
Page 55
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 55 AtkinsRéalis - Baseline / Référence 4.3.3.8 Dunedin Terrace The integrated modelling indicates that flooding within the Dunedin Terrace hotspot is limited and largely confined to isolated low points along North Douglas Street and Dunedin Terrace. The model predicts only shallow flooding, with very little flooding exceeding 0.3 m in depth, suggesting limited potential for significant impacts to properties or infrastructure. These findings are consistent with the conclusions of the desktop root cause analysis. As discussed in Section 4.2, the updated 2025 SEPA Flood Maps indicate a notable reduction in the extent and severity of surface water flooding at this location compared to the previous dataset, with fewer properties shown to be at risk and only limited areas of deeper flooding identified. The integrated model results are therefore more closely aligned with the updated SEPA mapping than with the previous flood maps. In addition, no historical flooding records were identified from WDC or other available sources to support the existence of a significant flood risk at this location. Consequently, whilst the modelling indicates that localised ponding may occur during intense rainfall events, the combined evidence from the updated SEPA mapping, hydraulic modelling and available flood records suggests that the overall level of flood risk at Dunedin Terrace is relatively limited compared to the other hotspots assessed within the study area. Figure 4-38 - Integrated model predicted flooding compared to SEPA pluvial flood maps (200 year RP)
Page 56
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 56 AtkinsRéalis - Baseline / Référence 4.3.3.9 Kilbowie Road The integrated modelling indicates that flooding within the Kilbowie Road hotspot is concentrated along Coldstream Road, with overland flow conveyed from higher ground to the east, including the wider Livingstone Street area. Additional localised ponding is also predicted within parts of the Clyde Shopping Centre area. The model results indicate flooding depths that could result in disruption to the local road network and access routes during intense rainfall events. The integrated model results show good agreement with both the original and updated SEPA surface water flood maps, which consistently identify this location as being susceptible to flooding. Although the 2025 SEPA Flood Maps indicate a modest reduction in the extent of flood risk compared to the previous dataset, significant areas of flooding remain evident within both the SEPA mapping and the integrated model predictions. As discussed in the desktop root cause analysis, whilst no historical flooding records were identified from WDC, media reports and information from ScW indicate a history of flooding and drainage-related issues within the wider area. In particular, the proximity of sewer flooding records at Cambridge Avenue suggests that sewer network performance may also influence flooding mechanisms locally. Consequently, the available evidence indicates that Kilbowie Road remains an area of flood susceptibility, with flood risk influenced primarily by surface water runoff, whilst sewer network constraints may also contribute to flooding within the wider catchment. Figure 4-39 - Integrated model predicted flooding compared to SEPA pluvial flood maps (200 year RP) 4.3.3.10 Station Road Due to limitations on the extent of network model, this hotspot was not assessed in the pluvial model.
Page 57
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 57 AtkinsRéalis - Baseline / Référence 4.3.3.11 Dumbarton Road (west) Due to limitations on the extent of network model, this hotspot was not assessed in the pluvial model. 4.3.4 Model Limitations At all times, reasonable skill and care has been used to ensure that the model was updated to best represent the physical nature and hydraulic performance of the catchment, within the confines of the Client Brief and Client Budget. It is highlighted that models only represent aspects of systems which we can both understand and quantify, and running simulations in a model environment carries limitations associated with required simplification and uncertainties including, but not limited to, the point outlined below. A number of key flooding mechanisms identified during the desktop review and stakeholder engagement are not fully represented within the hydraulic model. These include the unnamed watercourse at Duntocher Road, which is currently being investigated by ScW due to its potential interaction with the combined sewer network, and historic drainage features within the Livingstone Street/Linnvale area that may influence sewer performance. As a result, the contribution of these systems to observed flooding remains uncertain. The calibration of this model is based on a combination of historical anecdotal evidence (the RP’s of historical events are not known), and SEPA surface water depth flood maps. As no measured data or evidence of depths of flooding at flooding hotspots has been provided to calibrate the model against, the exercise is considered an assessment of the predicted flows which may reach each hotspot based on the data provided. While the Dalmuir ScW models were used as a basis for the SWMP, following updates to the surfaces to more accurately understand pluvial flooding, some impact on previous flow survey verification has occurred. Sense checks have been undertaken on flows in the ScW sewer system, and no reverification has been undertaken using historic flow survey data. Therefore, the model is considered to underpredict the flows that enter the sewer system, however, it is considered conservative for assessment of surface flows for the purpose of the LA SWMP. Gullies are typically designed to operate up to a 1 in 5-year RP event, and so their impact is considered limited for the larger RP’s used to assess flooding in this model. The losses into the sewer system that would occur from their representation therefore means that potential flows into the piped system are more limited than in reality. 1D subcatchments, typically used to generate runoff in a sewer model (as per the ScW baseline) route runoff directly into the piped network. This can be conservative for flows more than the design of gullies in terms of out-of-sewer flooding in the 1D model. All simulations represent current climate conditions. In other words, future design horizons were not represented (increases in population, impacts of climate change, etc), so options developed will not consider the future performance of the catchment. The model should be used with caution when assessing out-of-sewer flooding and the effectiveness of proposed mitigation measures. Since completion of the original SWMP, additional information has become available through the updated 2025 SEPA Flood Maps, stakeholder engagement and ongoing ScW investigations. These investigations have identified uncertainties regarding sewer connectivity and flooding mechanisms at a number of hotspots. Any future use of the model to support option development or detailed design should therefore be preceded by further model review, updating and reverification where appropriate. 4.3.5 Future Flood Risk A multitude of factors influence flood hazard and flood risk. The main factors are: Climate Land use (urban creep can greatly influence surface water flooding) Demographics
Page 58
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 58 AtkinsRéalis - Baseline / Référence It is important to understand how these factors will influence flood risk in the future so that holistic judgement can be made, and appropriate actions can be taken to sustainably manage flood risk now and in the future. Key information that helps to make this holistic judgement is: Understanding where significant flood risks may arise in the future and which areas are more susceptible to change. Understanding and deciding which actions can be taken now to mitigate changes in the future. Consider the longevity of actions to ensure that actions taken now are resilient and adaptable to future change. Prioritise actions – actions in an area that is highly sensitive to climate change should be given greater importance.
Page 59
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 59 AtkinsRéalis - Baseline / Référence 5. Set Objectives In line with the Scottish Government’s SWMP guidance, the indicators used for the flood risk objectives were the ‘at-risk’ receptors. Objectives were prioritised to help clarify which factors should be addressed first (i.e., in the short term) and which factors can be addressed in the medium to longer term. The category used to help prioritise were: Surface water flood risk (using information on flooding impact) Surface water flood risk to priority receptor groups (e.g., homes at risk in more socially vulnerable areas). Locations with a history of flooding Areas where there is no history of flooding, but which are predicted to flood and should be treated with caution (particularly where more detailed modelling is not available). Locations where there are opportunities for joint working (for example, making management more cost- effective and delivering multiple benefits). The hotspot areas are summarised in Table 5-1 below with each hotspot classified in terms of priority. It should be noted that this assessment was undertaken as part of the initial SWMP submission in April 2024 and does not take into account the updates discussed associated with the change in flood risk attributed to the 2025 SEPA flood maps Table 5-1 Objectives Location / Hotspot History of flooding confidence in data Initial Objective Initial Priority Homes (1 in 30 year) Loss in Economic Activity Safety Concerns Second Avenue / Ramsay Street SEPA pluvial flood maps and historic flood data. Sewer flooding. Improve understanding of surface water flooding in area. High 12 Roads impacted Western Isles Road SEPA pluvial Flood Maps and historic flood data Improve understanding of surface water flooding in area. High 31 Duntocher Road SEPA pluvial flood maps and historic flood data. Sewer flooding. Improve understanding of surface water flooding in area. High 0 1m deep flooding on roads Livingstone Street SEPA pluvial flood maps and historic flood data. Sewer flooding. Improve understanding of surface water flooding in area. High 14 Road Melbourne Avenue SEPA pluvial flood maps and historic flood data Improve understanding of surface water flooding in area. High 0 0.9m deep flooding on roads Low Crescent SEPA pluvial & fluvial flood maps and historic flood Improve understanding of surface water flooding in area. Med 52
Page 60
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 60 AtkinsRéalis - Baseline / Référence data. Sewer flooding. Dumbarton Road SEPA pluvial flood maps and historic flood data Improve understanding of surface water flooding in area. Med 0 Dunedin Terrace SEPA pluvial flood maps Improve understanding of surface water flooding in area. Med Large block of flats Road Kilbowie Road SEPA pluvial flood maps and historic flood data Improve understanding of surface water flooding in area. Med 0 Station Road* SEPA pluvial flood maps and historic flood data Improve understanding of surface water flooding in area. High* 0 Dumbarton Road (west) SEPA pluvial flood maps and historic flood data Improve understanding of surface water flooding in area. Med 0 *WDC requested that the Station Road hotspot be included as a high priority hotspot following the initial submission of this report, due to this, Station Road was not included in the initial options appraisal.
Page 61
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 61 AtkinsRéalis - Baseline / Référence 6. Option Appraisal 6.1 Scoping Option Appraisal The options appraisal and development of preferred measures presented in this section were undertaken as part of the initial SWMP submission and were based on the best available information at that time, including historical flood records, stakeholder information, hydraulic modelling outputs and the SEPA Flood Maps then available. A detailed appraisal was undertaken for the identified high-priority hotspots, whilst medium and lower priority locations were assessed at a higher level to identify potential future actions and investigations. Following completion of the initial assessment, additional information became available through the December 2025 stakeholder workshop involving WDC, ScW, Network Rail and Scottish Canals, together with subsequent stakeholder engagement and the publication of the updated 2025 SEPA Flood Maps. This information provided further insight into flood mechanisms, interactions between surface water, sewer, watercourse, canal and railway drainage systems, and highlighted data gaps and ongoing investigations that influence the understanding of flood risk at several locations. In some cases, the updated SEPA mapping also resulted in changes to the extent and significance of previously identified hotspots. The options appraisal presented in the following sections should therefore be viewed within the context of the information available at the time it was undertaken. While the assessment remains valuable in identifying potential flood risk management opportunities, the findings should be reviewed alongside the updated hotspot assessments, stakeholder feedback and the outcomes of ongoing investigations before progressing any preferred options. In particular, collaboration with ScW is recommended for the Dalmuir System Plan, in which they are looking understand where local authority needs/investment is planned and how that can possibly link to their own investment. The prioritisation adopted for the original options appraisal is outlined in Table 6-1 Table 6-1 Prioritisation of hotspots for Option Appraisal. Location History of flooding / confidence in data (2024) Initial Objective Initial Priority Include in Option Appraisal (2024) 2026 update Second Avenue / Ramsay Street SEPA pluvial flood maps and historic flood data Sewer flooding. Reduce surface water flooding High Yes Collaboration with ScW to reduce surface water and out of sewer flooding Western Isles Road SEPA pluvial Flood Maps and historic flood data Reduce surface water flooding High Yes Collaboration with ScW to reduce surface water and out of sewer flooding Duntocher Road SEPA pluvial flood maps and historic flood data Sewer flooding. Reduce surface water flooding High Yes Collaboration with ScW to reduce surface water and out of sewer flooding Livingstone Street SEPA pluvial flood maps and historic flood data Sewer flooding. Reduce surface water flooding High Yes Collaboration with ScW to reduce surface water and out
Page 62
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 62 AtkinsRéalis - Baseline / Référence of sewer flooding Melbourne Avenue SEPA pluvial flood maps and historic flood data Reduce surface water flooding High Yes Collaboration with ScW to reduce surface water and out of sewer flooding Low Crescent SEPA pluvial & fluvial flood maps and historic flood data Sewer flooding. Reduce surface water flooding Medium Not at this time – action can be for future option appraisal Pluvial flooding no longer main driver based on updated dataset. Dumbarton Road SEPA pluvial flood maps and historic flood data Reduce surface water flooding Medium Not at this time – action can be for future option appraisal Pluvial flooding no longer main driver based on updated dataset. Dunedin Terrace SEPA pluvial flood maps Reduce surface water flooding Medium Not at this time – action can be for future option appraisal Pluvial flooding no longer main driver based on updated dataset. Kilbowie Road SEPA pluvial flood maps and historic flood data Reduce surface water flooding Medium Not at this time – action can be for future option appraisal Not at this time – action can be for future option appraisal Station Road* SEPA pluvial flood maps and historic flood data Reduce surface water flooding High* Not at this time – action can be for future option appraisal Added as a high priority hotspot following the previous submission Dumbarton Road (west) SEPA pluvial flood maps and historic flood data Reduce surface water flooding Medium Not at this time – action can be for future option appraisal Not at this time – action can be for future option appraisal *WDC requested that the Station Road hotspot be included as a high priority hotspot following the initial submission of this report, due to this, Station Road was not included in the initial options appraisal.
Page 63
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 63 AtkinsRéalis - Baseline / Référence 6.2 Options Assessed A wide range of measures were considered for potential use in the hotspot areas to reduce surface water flooding. Both non-structural and structural measures were considered. 6.2.1 Non-Structural The non-structural and structural measures that were investigated are outlined in Table 6-2. Table 6-2 Table outlining non-structural intervention measures to reduce surface water flooding, as outlined in the Flood Risk Management (Scotland) Act 2009: Surface Water Management Planning Guidance. Action Action Description Notes Land use planning policy – adhere to existing New development should not be at risk of surface water flooding and does not increase flooding elsewhere. To achieve this, surface water (drainage and flooding) should be managed sustainably above- ground and should integrate with and enhance the urban landscape. This requirement will continue to apply. It is considered difficult to implement more stringent policies because of WDC’s competing ‘One Plan One Place’ objective. Land use planning policy – implement more stringent policies New developments may have the potential to reduce existing flood risks. Where this is possible local policies (e.g., In supplementary planning guidance) to implement this should be put in place for development planning and development management. Clarify responsibilities for new surface water management infrastructure Clarify ownership and vesting processes for all surface water management and infrastructure in new developments (drainage and flooding up to 1 in 200-year rainfall event) and set out how they will work with the land use planning system to meet required planning policies. Clarify responsibilities for existing surface water management infrastructure Clarify and agree ownership for maintaining existing surface water management infrastructure (including SuDS) Emergency response plans Use information about surface water flood risk to improve emergency response plans
Page 64
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 64 AtkinsRéalis - Baseline / Référence Study – improve understanding Carry out modelling and other assessments to improve knowledge of flood hazards and risk (adverse impact) Currently underway Study – option appraisal and design Further study to appraise management options in more detail or take a preferred option to detailed design. Currently underway Study – improve information on surface water flood events Improve data collection on surface water flood events when they occur, to improve knowledge of surface water flood risk and improve confidence in surface water flood models. It is recommended that WDC improve their data collection and recording of flooding events. Self-help – community flood action groups and resilient community plans Self-help –-property- level protection Increase the resilience of individuals and businesses through self-help actions, helping to ensure that people, communities, and businesses are prepared for flooding, knowing what action they can take and can recover quickly afterwards. Door flood door or barrier (manually fitted), air brick cover, install non-return valves on drainage outlets, pointing or waterproofing brickwork, raise vulnerable features such as electrical sockets above floor level, submersible pump. Self-help –-property- level resilience (retrofit) Flood forecasting and warning Develop surface water flood forecasting, alerts, and warning systems. SEPA issues surface water flood forecasting and alerts but does not currently provide surface water flood warnings. Other authorities may contact SEPA for advice on installing local schemes. Asset management and maintenance Review and change existing systems for inspecting and maintaining surface water management infrastructure e.g., culverts, SUDS, sewers, and road drainage. Watercourse management and maintenance Review and change existing systems for inspecting and maintaining urban burns.
Page 65
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 65 AtkinsRéalis - Baseline / Référence Relocation Relocate properties or infrastructure away from flood risk areas. 6.2.2 Structural The structural measures that were investigated are outlined in Table 6-3. Table 6-3 – Table outlining structural above ground intervention measures to reduce surface water flooding, as outlined in the Flood Risk Management (Scotland) Act 2009: Surface Water Management Planning Guidance. Action Action Description Notes Restoring urban watercourses Restore urban watercourse (e.g., restoring floodplains and deculverting) to reduce flooding from watercourse itself and provide more opportunities to convey surface water into the natural environment. Urban water engineering Storage (online or offline storage), embankments, walls, or flood diversion channel in urban burns. Runoff reduction strategy Develop a long-term plan for making whole urban areas greener and more permeable and reducing grey surfaces. Green infrastructure allows more rain to infiltrate the ground and encourages evapotranspiration in the atmosphere, reducing runoff rates and volumes. This can help manage frequent rainfall events, mitigate urban creep and adapt to climate change. Reducing surface water in sewer Identify opportunities to reduce surface water in sewers. ScW is responsible for the sewer network and should be contacted regarding any proposals. WDC may see opportunities when managing surface water flooding or where sewer network overflows may be contributing to surface water flooding problems. ScW and WDC should coordinate work to realise multiple benefits. Land management - NFM Implement land management actions that reduce the rate and volume of runoff. Runoff from more rural land can flood homes, businesses, and infrastructure
Page 66
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 66 AtkinsRéalis - Baseline / Référence directly and, by significantly increasing flows to urban areas, drainage systems and watercourse can raise flood risk further downstream. Underground storage Divert surface water to storage tanks or by providing storage in the existing drainage / flood management network. Underground conveyance Increase capacity or build new underground pipes for surface water Modification of culverted watercourses Increase the capacity of culverted watercourses or divert culverted watercourses The importance of the sustainable management of water is becoming increasingly evident because of the ever- increasing pressures placed on natural resources because of various factors such as: increasing population and increasing food demands, (trend towards wetter winters and drier summers). Therefore, it is no surprise that the sustainable management of water is a catalyst for economic growth, social change, improved public health (both physical and mental) and improved resilience to adapt to the constantly changing climate because of climate change impacts and the uncertainties associated with climate change. WDC strongly recognise this and prefer above ground sustainable solutions where feasible and cost-effective. 6.2.3 Property Level Protection Flood water can enter a property through a variety of mechanisms. For example: Entry at air bricks Entry through party walls from property next door if it is flooded. Entry through cracks in brickwork Seepage through ground entering through the floors of basements and cellars. Backflow through overloaded drainage/sewer system blocked by flooding. Entry at the damp-proof course Entry through permeable brickwork and weathered or damaged mortar. Entry at gaps and cracks in joint sealant around doors and windows Entry through gaps around pipes and cable pass throughs in walls and floors
Page 67
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 67 AtkinsRéalis - Baseline / Référence Figure 6-1 – Different mechanisms of flood water entry into properties. 6.2.4 SuDS Types The SuDS types investigated in the options appraisal are summarised in Table 6-4. Table 6-4 Table outlining SuDS measures considered. SuDS Measure Brief description of all 15 types Green roofs (1) Planted roof suitable for large flat roofed buildings
Page 68
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 68 AtkinsRéalis - Baseline / Référence Water butts (2) Private solutions for storing water installed on residential buildings by diverting existing rainwater downpipes into water butts Various permeable pavings and soakaways (3) Permeable paving: Permeable surface with underground gravel or plastic boxes storage space (4) Gravel paving: Gravel surface providing some storage suitable for car parks etc. (5) Filter drains: Trench filled with gravel allowing some storage (6) Soakaways: Excavation filled with gravel or plastic boxes (to allow water infiltration into the ground) and covered with soil (7) Disconnecting downpipes: Disconnected rainwater downpipes from large buildings into underground storage usually beneath permeable pavements Raingardens (8) Bioretention: Includes pocket infiltration, bioretention and multiple tree pits. The same set up as rain gardens (surface) but separated in assessment as they are supposed to take runoff from roads whilst surface rain gardens only from residential roofs. (9) Single tree pits with storage beneath Raingardens either: (10) Rain garden (box) 1m high boxes with voids for water storage and surface planting
Page 69
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 69 AtkinsRéalis - Baseline / Référence (11) Raingardens (surface): Residential solution consisting of surface planting with limited storage capacity to direct runoff from roof or hardstanding into these raingardens, or (12) Attenuating rain gardens: Raingardens with additional storage beneath in a form of gravel or plastic boxes storage more suitable for larger public spaces Large nature-based solutions (13) Swales: Large grassed channels, includes wet and dry, linear and round solutions (14) Ponds: Suitable in large natural spaces only (15) Wetlands: Shallow features suitable only in large natural spaces
Page 70
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 70 AtkinsRéalis - Baseline / Référence 6.3 Develop Preferred Option / Screening The long list of options presented in this section were developed as part of the previous SWMP submission in April 2024, based on the understanding of flood risk and flooding mechanisms available at that time. The options were informed by the root cause analysis, hydraulic modelling and stakeholder information available during the original assessment and were intended to identify potential opportunities to manage flood risk at each hotspot. The long list of options was developed taking cognisance of: Meeting the objectives outlined in Section 5; Promoting a sustainable approach to flood risk management; and Working collaboratively with stakeholders. As previously noted, since completion of the original options appraisal, additional information has become available through the December 2025 stakeholder workshop, subsequent stakeholder engagement, ongoing investigations and publication of the 2025 SEPA Flood Maps. This information has improved understanding of the interactions between surface water flooding, sewer systems, watercourses, transport infrastructure and other stakeholder assets across the catchment. It has also identified a number of data gaps and highlighted the interconnected nature of flooding mechanisms within Clydebank. As a result, the options identified within the original appraisal should be reviewed in the context of this updated understanding of flood risk. In particular, the workshop discussions highlighted the need for a more strategic and collaborative catchment-wide approach, recognising that opportunities associated with ScW, Network Rail, Scottish Canals, WDC and other stakeholders' assets may provide greater benefits than individual hotspot- specific interventions delivered in isolation. It should be noted that the existing sewer system is understood to have little or no spare capacity for additional flows. However, Scottish Canals have advised that they would be open to considering this, and the potential for doing so can be investigated further. The options presented in the following sections should therefore be considered as an initial evidence base that can inform future strategic option development and partnership working across the wider catchment. 6.3.1 Second Avenue / Ramsay Street The Second Avenue / Ramsey Street hotspot was identified during the initial SWMP assessment due to historical flooding records, significant road flooding and evidence of sewer network exceedance. The long list of options identified for Second Avenue / Ramsay Street is outlined in Table 6-5 and illustrated in Figure 6-2. Table 6-5 - Options outlined for Second Avenue No Location Option 1a Park Road Park Avenue junction with B814 – remove redundant bus only arm and replace with attenuation basin 1b Park Road Park Avenue junction with B814 – remove redundant bus only arm and replace with underground storage tank 2a Second Avenue (stretch between Park Road and St Stephen’s Primary School) Install a new additional sewer to convey flow to St Stephen’s Primary School and attenuate within the school (rain garden or swale to convey flow) – road width to be reduced by 1.5m 2b Second Avenue (stretch between Park Road and St Stephen’s Primary School) Install a new additional sewer to convey flow to St Stephen’s Primary School and attenuate within the school (engineered channel) – road width to be reduced by 1.5m 3 Duntocher Road Install a rain garden or shallow swale and reduce road width along Duntocher road by 2-3m 4 Duntocher Road (Option 1 in the Duntocher Road Hotspot) SuDs Basin
Page 71
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 71 AtkinsRéalis - Baseline / Référence Figure 6-2 - Options outlined for Second Avenue As discussed in the root cause analysis, the flooding mechanism at Second Avenue / Ramsay Street is influenced by a combination of surface water runoff and sewer flooding, and is hydraulically linked to the wider catchment upstream at the Duntocher Road hotspot (see Section 6.3.3 for a summary of options at this hotspot). The root cause analysis identified that runoff conveyed through the catchment has the potential to influence flooding at both locations. ScW is currently undertaking investigations to improve understanding of the interactions between the sewer network, storm drainage systems and the unnamed watercourse within the wider area, and the outcomes of these investigations are expected to provide important information regarding the sources of flooding and performance of the drainage system. Consequently, the options identified for Second Avenue / Ramsay Street should be reviewed in light of the findings of the ongoing ScW investigations before being progressed further. In particular, due to the hydraulic linkages, options proposed at Duntocher Road may provide benefits to the downstream Second Avenue / Ramsay Street hotspot through attenuation of runoff and reduction of flows conveyed through the catchment. However, the uncertainties associated with the current understanding of flooding mechanisms, including the role of the unnamed watercourse and sewer network interactions, should be taken into account when assessing the likely effectiveness of these measures. Given the significant contribution from sewer flooding at this location, a collaborative approach between WDC and ScW will be required to identify the most appropriate long-term solution. If a detention basin or similar surface water storage feature is progressed in isolation of a wider strategic approach, consideration should be given to the potential presence of out-of-sewer flooding within stored floodwaters. In such circumstances, appropriate water quality and biological treatment measures may be required to manage risks associated with contaminated floodwaters and ensure compliance with relevant environmental and public health requirements.
Page 72
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 72 AtkinsRéalis - Baseline / Référence 6.3.2 Western Isles Road The Western Isles Road hotspot was identified during the initial SWMP assessment due to historical flooding records, reported sewer surcharging, evidence of sewer network exceedance and the low-lying topography surrounding Durban Avenue, which contributes to localised ponding during heavy rainfall events. The root cause analysis identified a combination of surface water runoff and sewer flooding, with sewer capacity constraints considered a significant contributor to flood risk at this location. The long list of options identified for Dunbarton Road is outlined in Table 6-6 and illustrated in Error! Reference source not found.. Table 6-6 Options outlined for Western Isles Road. No Location Option 1a Western Isles Road (junction with Dumbarton Road) Kerb inlets within south arm of the roundabout to collect surface water in centre of roundabout, attenuate and convey to playpark between Dumbarton Road and Durban Avenue (SuDS basin) 1b Western Isles Road (junction with Dumbarton Road) Kerb inlets within north arm of the roundabout to collect surface water in centre of roundabout, attenuate and convey to playpark between Dumbarton Road and Durban Avenue (underground storage tank) 2 Western Isle Road (Greenspace between Western Isles Road and Dumbarton Road SuDS basin or SuDS Pond to attenuate runoff and discharge at greenfield rate into sewer 3 Western Isle Road Roadside swales to convey and attenuate surface water and store in the park 4 Iona Place Speed bump where Iona Place meets Western Isle Road to prevent additional flow entering Iona Place
Page 73
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 73 AtkinsRéalis - Baseline / Référence Figure 6-3 - Options outlined Western Isles Road 6.3.3 Duntocher Road The Duntocher Road hotspot was identified during the initial SWMP assessment due to historical flooding records, significant road flooding and evidence of sewer network exceedance. The long list of options identified for Duntocher Road is outlined in Table 6-7 and illustrated in Figure 6-4. Table 6-7 Options outlined for Duntocher Road. No Location Option 1 In grassy area immediately west of the Kilbowie Roundabout (between the A82 and Duntocher Road) SuDS basin providing surface water attenuation prior to discharge into the sewer network 2 In the grassy verge between the A82 east and west bound roads (north-west of the Kilbowie Roundabout) Roadside swale providing conveyance and attenuation of surface water prior to discharge into the sewer network 3 In grassy area immediately north of the Kilbowie Roundabout (between the A82 and Kilbowie Road) SuDS basin providing surface water attenuation prior to discharge into the sewer network 4 Centre of the Kilbowie Roundabout SuDS basin providing localised surface water attenuation prior to discharge into the sewer network 5 Green space south of the A82 (south- east of the Kilbowie Roundabout) SuDS basin providing surface water attenuation prior to discharge into the sewer network 6 Kilbowie Park and Ride Permeable paving to reduce runoff rates and volumes discharged to the sewer network
Page 74
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 74 AtkinsRéalis - Baseline / Référence Figure 6-4 - Options outlined Duntocher Road As discussed in the root cause analysis, the flooding mechanism at Duntocher Road is not yet fully understood due to uncertainties surrounding the interaction between the sewer network, the storm drainage system and the unnamed watercourse running parallel to the road. ScW is currently undertaking investigations to better understand these interactions, including the potential connectivity between the unnamed watercourse and the combined sewer network. The outcomes of these investigations are expected to provide important information regarding the sources of flooding and the performance of the drainage system at this location. Consequently, the options identified for Duntocher Road should be reviewed in light of the findings of the ongoing ScW investigations before being progressed further. In particular, any future option development should consider the potential influence of the unnamed watercourse, the storm drainage outfalls to the adjacent parkland and any identified sewer network constraints to ensure that measures do not create downstream detriment or inadvertently increase flood risk elsewhere within the catchment. Given the complex and interconnected nature of the flooding mechanisms at this site, together with the significant contribution from sewer flooding, a collaborative approach between WDC and ScW will be required to identify the most appropriate long-term flood risk management solution. If a detention basin or similar surface water storage feature is progressed at this location in isolation of a wider strategic solution, consideration should be given to the potential presence of out-of-sewer flooding within the stored floodwaters. In such circumstances, appropriate water quality and biological treatment measures may be required to manage the risk associated with contaminated floodwaters and to ensure compliance with relevant environmental and public health requirements.
Page 75
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 75 AtkinsRéalis - Baseline / Référence 6.3.4 Livingstone Street The Livingstone Street hotspot was identified during the initial SWMP assessment due to historical flooding records, the strategic importance of the road as the sole vehicular access route into Linnvale, and evidence of sewer network exceedance. The long list of options identified for Livingstone Street is outlined in Table 6-8 and illustrated in Figure 6-5. Table 6-8 Options outlined for Livingstone Street. No Location Option 1 Grassy verge south of Livingstone Street SuDS Basin 2 Clyde Retail Park Disconnect large commercial roof downpipes and store in underground storage below the parking areas. 3 Linnvale Primary School Disconnect roof downpipes from the school into rain gardens, SuDS, or underground storage 4 Linnvale Primary School Minimise extent of impermeable surfacing in the playground area to reduce runoff generated from the school grounds. 5 North of Shinwell Avenue and railway Take into account investigations by ScW whether there is an upstream watercourse contributing flow into the combined sewer through a drainage survey in this location. If an upstream connection is found a short-term flow survey may help to verify flows experience here and understand how much this is contributing to flooding in the Livingstone Street area. Figure 6-5 - Options outlined for Livingstone Street As discussed in the root cause analysis, the flooding mechanism at Livingstone Street is influenced by interactions between surface water runoff and the sewer network. However, the updated 2025 SEPA Flood Maps indicate a substantial reduction in predicted pluvial flood risk compared to the mapping used during the initial SWMP assessment, suggesting that widespread surface water flooding is less significant than originally
Page 76
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 76 AtkinsRéalis - Baseline / Référence anticipated. Ongoing ScW investigations, including consideration of the potential interaction between historic drainage features and the combined sewer network, are expected to further improve understanding of the flooding mechanism at this location. Consequently, the options identified for Livingstone Street should be reviewed in light of the updated flood mapping and the outcomes of the ongoing ScW investigations before being progressed further. While the original options were developed primarily to manage surface water runoff, they may still provide benefits by reducing inflows to the sewer network and helping to alleviate sewer exceedance during heavy rainfall events. Given the evidence that sewer flooding may be a primary contributor to flood risk at this location, a collaborative approach between WDC and ScW will be required to identify appropriate long-term solutions. Future option development should therefore focus on opportunities that provide integrated benefits to both surface water and sewer systems and should be considered within the context of wider strategic investigations being undertaken across the catchment. 6.3.5 Melbourne Avenue The Melbourne Avenue hotspot was identified during the initial SWMP assessment due to historical flooding records, recurring drainage issues and evidence of sewer network exceedance. The root cause analysis found that flooding is concentrated around the low point on Melbourne Avenue and is associated with a combination of surface water runoff, blocked drainage infrastructure and surcharge from the combined sewer network. Avenue, indicating that sewer capacity constraints are a significant contributor to the observed flood risk. The long list of options identified for Melbourne Avenue is outlined in Table 6-9 and illustrated in Figure 6-6. Table 6-9 Options outlined for Melbourne Avenue. No Location Option 1 Melbourne Avenue Swale to west of Melbourne Avenue across from the bus shelter 2 Melbourne Avenue Swale and geocellular crate below to the west of Melbourne Avenue across from the bus shelter 3 Melbourne Avenue New over-sized surface water sewer system that connects back into the combined system just north-west of the existing play park area but could have a separate outfall in the future (designed to have an overland flow path down Salisbury Place).
Page 77
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 77 AtkinsRéalis - Baseline / Référence Figure 6-6 - Options outlined for Melbourne Avenue
Page 78
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 78 AtkinsRéalis - Baseline / Référence 6.4 Prioritising Options The long list of solutions has been screened using a multi-criteria assessment to reduce the number of potential measures taken forward for further consideration. The purpose of this process is to focus subsequent appraisal on those options that are considered most likely to provide a viable means of managing flood risk. The multi-criteria analysis is based on a high-level assessment of relative cost, feasibility and effectiveness at reducing flood volume. This prioritisation does not represent a detailed cost benefit analysis, nor does it account for all site-specific constraints, planning considerations or potential stakeholder input. The feasibility and effectiveness of the options should be reviewed further at design stage when data from more detailed investigations is available. Accordingly, this prioritisation should be treated as indicative. In addition, the feasibility and effectiveness of potential measures should be reviewed in consultation with WDC, ScW and other relevant stakeholders to ensure that wider drainage system interactions, ongoing investigations and catchment-wide objectives are appropriately considered. Options highlighted in green scored the highest. In certain instances, multiple options have been shortlisted for consideration together, reflecting their complementary strengths. The four key criteria used for screening unfeasible actions were: Sustainability (environmental, economic and social sustainability); Technical feasibility; Legal and planning considerations; and Effectiveness in reducing flood risk. Table 6-10 shows the scoring criteria that was applied when performing the multi-criteria assessment. Table 6-10 - Multi-Criteria Assessment Scoring Criteria Public or Private Planned Resurfacing Volume Attenuated Relative Cost Technical Feasibility Effectiveness at removing flow volumes – considers flow passing through and proximity to main flooding Total Score 1 (private) - 5 (public) 1 (no planned resurfacing) – 5 (planned resurfacing) 1 (limited attenuation capacity) – 5 (greater attenuation capacity) 1 (higher cost implications) – 5 (lower cost implications) 1 (complex) – 5 (limited perceived constraints) 1 (minimum effectiveness) – 10 (maximum effectiveness)
Page 79
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 79 AtkinsRéalis - Baseline / Référence 6.4.1 Second Avenue / Ramsay Street The multi-criteria assessment for Second Avenue / Ramsay Street is outlined in Table 6-11. Table 6-11 - Multi-Criteria Assessment for Second Avenue / Ramsay Street ID Option Location Public or Private Planned Resurfacing Volume Attenuated Relative Cost Technical Feasibility Effectiveness at removing flow volumes Total Score 1a Attenuation basin Park Road 5 1 3 3 3 6 21 1b Underground storage tank Park Road 5 1 4 2 2 5 19 2a New storm sewer and attenuation with raingarden or swale Second Avenue (stretch between Park Road and St Stephen’s Primary School) 5 1 2 3 3 4 18 2b New storm system and attenuation with engineered channel Second Avenue (stretch between Park Road and St Stephen’s Primary School) 5 1 4 2 3 6 21 3 Raingarden and swale Duntocher Road 5 1 2 2 2 2 14 4 SuDs basin Duntocher Road Basin (Duntocher Road Hotspot Option 1) 5 1 5 3 4 8 26
Page 80
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 80 AtkinsRéalis - Baseline / Référence 6.4.2 Western Isles Road The multi-criteria assessment for Western Isles Road is outlined in Table 6-12. Table 6-12 - Multi-Criteria Assessment for Western Isles Road ID Option Location Public or Private Planned Resurfacing Volume Attenuated Relative cost Technical Feasibility Effectiveness at Removing flow Volumes Total 1 SuDS basin Western Isles Road (junction with Dumbarton Road) 5 1 2 4 3 4 19 1b Underground storage tank Western Isles Road (junction with Dumbarton Road) 5 1 3 2 3 5 19 2 SuDS basin Western Isle Road (Greenspace between Western Isles Road and Dumbarton Road 5 1 4 3 3 5 21 3 Swale and attenuation in park Western Isles Road 5 1 4 4 4 6 24 4 Speed bump to divert flows Iona Place 5 1 1 3 4 1 15
Page 81
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 81 AtkinsRéalis - Baseline / Référence 6.4.3 Duntocher Road The multi-criteria assessment for Duntocher Road is outlined in Table 6-13. Table 6-13 - Multi-Criteria Assessment for Duntocher Road ID Option Location Public or private Planned resurfacing Volume Attenuated Relative Cost Technical Feasibility Effectiveness at removing flow volumes Total 1 SuDS Basin In grassy area immediately west of the Kilbowie Roundabout (between the A82 and Duntocher Road) 5 1 5 3 4 8 26 2 Swale In the grassy verge between the A82 east and west bound roads (north- west of the Kilbowie Roundabout) 5 1 3 3 4 6 22 3 SuDS Basin In grassy area immediately north of the Kilbowie Roundabout (between the A82 and Kilbowie Road) 5 1 5 3 4 6 24 4 SuDS Basin Centre of the Kilbowie Roundabout 5 1 3 3 3 5 20 5 SuDS Basin Green space south of the A82 (south-east of the Kilbowie Roundabout) 5 1 3 3 4 4 20 6 Permeable Paving Kilbowie Park and Ride 1 1 2 2 2 3 11
Page 82
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 82 AtkinsRéalis - Baseline / Référence 6.4.4 Livingstone Street The multi-criteria assessment for Livingstone Street is outlined in Table 6-14. Table 6-14 - Multi-Criteria Assessment for Livingstone Street. ID Option Location Public or private Planned resurfacing Volume Attenuated Relative Cost Technical Feasibility Effectiveness at removing flow volumes Total 1 SuDS Basin Grassy verge south of Livingstone Street 5 1 4 3 4 6 23 2 Commercial roof disconnection and attenuation Clyde Retail Park 1 1 2 1 3 3 11 3 School roof disconnection and attenuation Linnvale Primary School 1 1 2 1 3 3 11 4 De-paving in school Linnvale Primary School 1 1 2 2 3 3 12 5 Upstream inflow investigation Shinwell Avenue N/A N/A N/A N/A N/A N/A -
Page 83
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 83 AtkinsRéalis - Baseline / Référence 6.4.5 Melbourne Avenue The multi-criteria assessment for Livingstone Street is outlined in Table 6-15. Table 6-15 - Multi-Criteria Assessment for Livingstone Street. ID Option Location Public or private Planned resurfacing Volume Relative Cost Technical Feasibility (Effectiveness at removing flow volumes) Total 1 Roadside swale Melbourne Avenue 5 1 3 4 5 4 22 2 Swale and geocellular storage Melbourne Avenue 5 1 4 3 4 6 23 3 Oversized surface water sewer Melbourne Avenue 5 1 3 2 3 4 18
Page 84
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 84 AtkinsRéalis - Baseline / Référence 6.5 Baseline: ‘Do minimum’ The baseline scenario against which the impacts and cost of other options can be compared against is the ‘do minimum’ option. The ‘do-minimum’ scenario was selected as the most appropriate baseline for surface water management. This is because there is a statutory requirement imposed on WDC to continue some surface water management activities. The ‘do-minimum’ scenario is the minimum existing actions carried forward to ensure adherence to statutory duties and responsibilities. For example: adherence to Scottish Planning Policy, duties for emergency response planning, agreement between responsible authorities as a matter of policy and, continuing asset management The ‘do-minimum’ scenario assumes that the baseline model drainage capacity (1 in 5-year drainage capacity if using SEPA pluvial modelling) is maintained. This means that an effective schedule of clearance and repair or inspection and maintenance regime of drainage infrastructure is performed by WDC. Moreover, once an existing structure reaches the end of its design life, it is assumed that it will be replaced. 6.6 Options: ‘Do something’ The ‘do something’ options were developed by combining the refined actions identified for each hotspot and were modelled as part of the initial SWMP submission using the information, flood mapping and hydraulic models available at that time. Since completion of the original assessment, additional information has become available through the December 2025 stakeholder workshop, publication of the 2025 SEPA Flood Maps, and ongoing ScW investigations across the Dalmuir catchment. As discussed throughout this report, this information has improved understanding of flooding mechanisms, identified a number of data gaps and uncertainties, and highlighted the significant interaction between surface water flooding, sewer network performance, watercourses and wider drainage infrastructure. Consequently, whilst the original option modelling provides a useful indication of the potential benefits of runoff reduction measures, the results and associated option performance assessments should now be considered superseded by the improved understanding of flood risk. The options developed during the initial assessment were largely hotspot-specific interventions, whereas the updated evidence demonstrates that flooding at many locations is strongly influenced by wider catchment processes, sewer network constraints and significant volumes of out-of-sewer flooding. It is therefore recommended that the previously developed options are not progressed on the basis of the original modelling alone and are instead reassessed as part of a more strategic and collaborative catchment-wide approach involving WDC, ScW and other key stakeholders. This reassessment should take account of the outcomes of ongoing investigations, updated flood risk information and links to the Dalmuir System Plan. Even where local runoff management measures remain appropriate, close collaboration with ScW will be required to ensure that residual sewer flood risk is adequately addressed and that interventions provide benefits at both the hotspot and wider catchment scale. Table 6-16 summarises the ‘Do Something’ standalone options identified in the multi criteria analysis. Table 6-16 – Summary of ‘Do Something’ options Hotspot Name No Location Option 1a Park Road Attenuation basin at junction
Page 85
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 85 AtkinsRéalis - Baseline / Référence Second Avenue/ Ramsey Street 2b Second Avenue (stretch between Park Road and St Stephen’s Primary School) Attenuation at school 4 Duntocher Road (Option 1 in the Duntocher Road Hotspot) SuDs Basin Western Isles Road 3 Western Isles Road Roadside swales Duntocher Road 1 In grassy area immediately west of the Kilbowie Roundabout (between the A82 and Duntocher Road) SuDs Basin Livingstone Street 1 Grassy verge south of Livingstone Street SuDs Basin Melbourne Avenue 2 Melbourne Avenue Swale and geocellular storage
Page 86
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 86 AtkinsRéalis - Baseline / Référence 7. Develop preferred option: confirm funding Sources of funding available for options within the Clydebank area were considered and these primarily sit with WDC because of the nature of the flooding (surface water) and how the responsibilities for implementation current sit. It should be recognised that these are other sources of funding available which may include: ScW maintenance ScW capital via quality and standard process Private funding (developer contributions) Other sources of funding ScW were engaged in the process and as it stands, they only have funding within their capital funding works for internal flooding up to the 10% Annual Exceedance Probability event (1 in 10 Year Return Period Event). Table 7-1 Actions Location Existing Action New Action (2026 update) Future Action Second Avenue / Ramsay Street Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Continue coordination with ScW and ongoing investigations; review flood mechanism and links with Duntocher Road hotspot; continue runoff reduction and blue-green infrastructure opportunities where appropriate. Review hotspot following ScW investigations and catchment studies; consider integrated catchment-scale options rather than standalone schemes. Western Isle Road Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Continue coordination with ScW regarding sewer flooding; maintain flood incident records and review any future flooding occurrences; continue runoff reduction strategy where opportunities arise. No further hotspot-specific option appraisal currently recommended. Review following outcomes of ScW investigations and links to the Dalmuir System Plan. Duntocher Road Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Support ongoing ScW investigations into the unnamed Review strategic opportunities once ScW investigations are complete; reassess hotspot- specific options in the context of wider catchment
Page 87
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 87 AtkinsRéalis - Baseline / Référence watercourse, sewer connectivity and drainage interactions; continue runoff reduction strategy and stakeholder collaboration. management and sewer constraints. Livingstone Street Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Continue coordination with ScW investigations into historic drainage features and sewer interactions; maintain records of flooding and access disruption; continue runoff reduction strategy where appropriate. Review previous options alongside ScW investigation outcomes. Prioritise measures delivering sewer and surface water benefits through a collaborative catchment approach. Melbourne Avenue Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Continue coordination with ScW due to significant sewer flooding mechanism; improve maintenance of local drainage assets; continue runoff reduction strategy where appropriate. Review existing options in conjunction with ScW investigations and wider sewer catchment constraints before progression. Low Crescent Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Continue monitoring of flooding incidents; review interaction of sewer, pluvial and fluvial mechanisms; coordinate with ScW regarding sewer flooding records. Future option appraisal if deemed appropriate based on model validation against real life data. Dumbarton Road Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Continue routine maintenance and monitor future flood incidents. No further hotspot-specific option appraisal currently recommended unless future evidence indicates a significant flood risk.
Page 88
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 88 AtkinsRéalis - Baseline / Référence Dunedin Terrace Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Continue routine maintenance and monitor future flood incidents. No further hotspot-specific option appraisal currently recommended given the limited flood risk identified in updated mapping and modelling. Kilbowie Road Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Continue monitoring of flooding incidents; coordinate with ScW regarding sewer network performance within the wider catchment; continue runoff reduction strategy. Review opportunities through wider catchment studies and links to the Dalmuir System Plan before progressing hotspot-specific measures. Station Road Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Maintain drainage assets and monitor interactions with adjacent watercourse and agricultural runoff; review emergency response procedures given strategic transport impacts. Consider future appraisal of options focused on protecting access and transport resilience if flooding continues to affect the route. Dumbarton Road (west) Road gully maintenance Flood incident records Update emergency response planning with new pluvial flood information Continue routine maintenance and monitoring of flood incidents. Review only if additional evidence of flooding becomes available.
Page 89
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 89 AtkinsRéalis - Baseline / Référence 8. Conclusions AtkinsRéalis was commissioned by WDC to develop a Surface Water Management Plan (SWMP) for Clydebank in accordance with the Flood Risk Management (Scotland) Act 2009 and the objectives of the Clyde and Loch Lomond Flood Risk Management Plan. The initial SWMP was completed and submitted in April 2024 based on the best available information at that time, including SEPA Flood Maps, historical flood records, stakeholder information and hydraulic modelling outputs. Since completion of the original assessment, additional information has become available through the publication of the 2025 SEPA Flood Maps, the December 2025 stakeholder workshop, subsequent engagement with key stakeholders and ongoing ScW investigations. This report has therefore revisited the original SWMP findings to review how this new information influences the understanding of flood risk, flooding mechanisms, hotspot prioritisation and future flood risk management recommendations across the Clydebank catchment. The review has demonstrated that the updated 2025 SEPA Flood Maps have reduced the extent of predicted surface water flood risk at several locations across Clydebank. As a result, a number of hotspots identified during the original assessment would no longer satisfy the original hotspot screening criteria if assessed using the updated mapping alone. However, the review has also demonstrated the importance of considering historical flooding records, stakeholder information and hydraulic model outputs alongside flood mapping when assessing flood risk and prioritising investment. A comprehensive review of the 2025 SEPA Flood Maps to identify any new flood risk hotspots has not been undertaken as part of this study. Future work should consider whether additional hotspots are warranted, taking into account the updated mapping and any reported flooding incidents since completion of the original SWMP. The desktop assessments, hydraulic modelling and stakeholder engagement have shown that flood risk within Clydebank is strongly influenced by the interaction between surface water runoff, sewer network exceedance, watercourses and other drainage infrastructure. Whilst pluvial flooding remains an important component of flood risk at some locations, the updated assessment indicates that sewer flooding is a significant contributor to flood risk at many of the priority hotspots, including Second Avenue / Ramsay Street, Western Isles Road, Duntocher Road, Livingstone Street, Melbourne Avenue and Low Crescent. In several locations, substantial volumes of out- of-sewer flooding were predicted, indicating that constraints within the Dalmuir sewer catchment are a key influence on the overall flooding mechanism. Table 8-1 summarises the outcome of the hotspot reassessment, including consideration of the 2025 SEPA Flood Maps, the principal flooding mechanisms identified at each location, and any discrete mitigation options identified through the initial Surface Water Management Plan (SWMP). The review has been undertaken in the context of the strategic approach to flood risk management recommended for the study area, recognising that while individual options may provide localised benefits, their effectiveness should be considered alongside wider catchment-scale interventions and opportunities across the drainage network. Table 8-1 – Summary of hotpots Hotspot Name 2025 SEPA Flood Map Reassessment Root Cause Summary No Location Option Second Avenue/ Ramsey Street Continues to meet criteria for surface water flood risk Combined sewer flooding resulting from limited sewer capacity, exacerbated by surface water runoff from the surrounding catchment. 1a Park Road Attenuation basin at junction 2b Second Avenue (stretch between Park Road and St Stephen’s Primary School) Attenuation at school 4 Duntocher Road (Option 1 in the SuDs Basin
Page 90
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 90 AtkinsRéalis - Baseline / Référence Duntocher Road Hotspot) Western Isles Road Continues to meet criteria based on impact on roads although no properties impacted Flooding is understood to be primarily driven by surface water runoff exceeding local drainage capacity. 3 Western Isles Road Roadside swales Duntocher Road Continues to meet criteria based on impact on roads although no properties impacted Sewer flooding associated with capacity exceedance in the drainage network, exacerbated by surface water runoff from the upstream catchment. 1 In grassy area immediately west of the Kilbowie Roundabout (between the A82 and Duntocher Road) SuDs Basin Livingstone Street No longer meets hotspot criteria, being investigated by ScW Sewer flooding resulting from capacity exceedance within the combined network, with contributions from surface water runoff and a potential fluvial inflow into sewer network being investigated. 1 Grassy verge south of Livingstone Street SuDs Basin Melbourne Avenue Continues to meet criteria based on impact on roads although no properties impacted Sewer flooding associated with limited drainage capacity, exacerbated by surface water runoff conveyed along local overland flow routes. 2 Melbourne Avenue Swale and geocellular storage Low Crescent No longer meets hotspot criteria Sewer flooding associated with limited drainage capacity, some surface water and fluvial influence Not selected for options appraisal Dumbarton Road No longer meets hotspot criteria No longer perceived to be at risk based on information available Not selected for options appraisal
Page 91
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 91 AtkinsRéalis - Baseline / Référence Dunedin Terrace No longer meets hotspot criteria No longer perceived to be at risk based on information available Not selected for options appraisal Kilbowie Road Continues to meet criteria due to impact on commercial properties Surface water flooding primary driver, with potential sewer flooding upstream of hotspot Not selected for options appraisal Station Road Continues to meet criteria based on impact on critical roads although no properties impacted Surface water with potential rural upstream influence Not selected for options appraisal Dumbarton Road (west) Continues to meet criteria based on impact on critical roads although no properties impacted Surface water with potential rural upstream influence Not selected for options appraisal The stakeholder workshop and subsequent discussions with ScW highlighted several uncertainties relating to drainage connectivity, sewer performance and the interaction between historic watercourses and the combined sewer network. In particular, ongoing investigations at Duntocher Road and Livingstone Street have identified important data gaps that may influence the understanding of flood mechanisms and the relative contribution of sewer flooding at these locations. Consequently, the findings of the hydraulic modelling should be interpreted alongside the identified model limitations and reviewed as the outcomes of ongoing investigations become available. The review also highlighted that many of the flood management options developed as part of the original SWMP were based on a more limited understanding of flood risk and were assessed as discrete hotspot-specific interventions. Since completion of that work, the improved understanding of flood mechanisms, together with ongoing investigations within the Dalmuir sewer catchment, has demonstrated that many flooding issues are linked through wider catchment processes and sewer network constraints. As a result, the original options and associated modelled benefits should be treated with caution and are considered to have been superseded by the improved understanding of flood risk now available. Overall, the findings of this SWMP indicate that many flood risk issues within Clydebank cannot be resolved through isolated local interventions alone. A coordinated and collaborative catchment-wide approach is therefore recommended, bringing together WDC, ScW, SEPA, Network Rail, Scottish Canals and other stakeholders to develop integrated solutions that address both surface water and sewer flooding mechanisms and deliver sustainable long-term flood risk management outcomes. 8.1 Recommendations This section summarises Further Actions and Stakeholders Engagement stage of SWMP. Given the ongoing investigations being undertaken by ScW and the improved understanding of flood mechanisms developed through this review, it is recommended that the findings of this study are used as a strategic evidence base to support future partnership working and development of integrated flood risk management solutions across Clydebank. The following recommendations are proposed: Continue engagement with ScW, SEPA, Network Rail and Scottish Canals to maintain the collaborative approach established through the December 2025 workshop.
Page 92
Clydebank Surface Water Management Plan_For Submission 07_26 1.0 | 16th July 2026 92 AtkinsRéalis - Baseline / Référence Review the 2025 SEPA Flood Maps to identify any additional flood risk hotspots, taking account of reported flooding incidents. Consider the findings of ongoing ScW investigations and links to the Dalmuir System Plan before progressing hotspot-specific flood alleviation measures, particularly where sewer flooding has been identified as a significant contributor to flood risk. Develop a catchment-wide flood risk management strategy that considers interactions between surface water runoff, sewer systems, watercourses, highway drainage and other infrastructure rather than addressing hotspots in isolation. Review and update hydraulic models as further information becomes available regarding sewer connectivity, historic watercourses and drainage system interactions. Reassess the flood management options developed as part of the initial SWMP in light of the updated understanding of flood risk, ongoing investigations and wider stakeholder initiatives before progressing to detailed appraisal or design. Undertake targeted surveys and investigations at locations where significant uncertainties remain regarding drainage connectivity, watercourse interactions and sewer network performance. Continue to improve flood incident recording, GIS management and data sharing between organisations to support model verification, future flood studies and evidence-based decision making. Identify opportunities to reduce flows entering the combined sewer network through retrofit SuDS, surface water separation, blue-green infrastructure and wider runoff reduction measures. Update emergency planning and operational procedures using the improved understanding of flood pathways, critical access routes and infrastructure dependencies developed through this study. Review the SWMP following completion of key stakeholder investigations and publication of updated strategic studies to ensure future investment decisions are based on the most up-to-date understanding of flood risk. Subject to continued collaboration between stakeholders and progression of ongoing investigations, the Clydebank SWMP provides a robust evidence base for developing a coordinated programme of flood risk management measures that improves resilience to both surface water and sewer flooding, while supporting long- term adaptation to future pressures including climate change
Page 93
AtkinsRéalis - Baseline / Référence APPENDICES
Page 94
Clydebank Surface Water Management Plan_For Submission 07_26 TBC 1.0 | 16th July 2026 94 AtkinsRéalis - Baseline / Référence Appendix A. Objectives Objective 1 Action Reference Action Status Responsibility Implementation Date Avoid an increase in surface water flood risk in Clydebank 1A Make sure all future development within the Clydebank area meets planning guidance (unless special regeneration areas or exempt areas which have been robustly justified) Existing WDC Ongoing Improve resilience to flooding 1B Update emergency response planning with new pluvial flood information New WDC 2026* Objective 2 Improve understanding of surface water flood risk in Clydebank 2A Continue to maintain and improve flood incident records and compare observed flooding with model predictions to support future model validation and refinement. Existing / Improved WDC 2024 onwards 2B Continue collaborative working with ScW, SEPA, Network Rail and Scottish Canals to improve understanding of flood mechanisms and identify opportunities for joint investment, in particular with links to the Dalmuir System Plan. Existing / Improved WDC 2024 onwards 2C Support and review the outcomes of ongoing ScW investigations into sewer flooding, drainage connectivity, historic watercourses and flooding mechanisms across the Dalmuir catchment. Existing WDC and ScW 2024 onwards 2D Review and update hydraulic models as additional information becomes available through ScW investigations, flood incidents and future studies. New WDC and ScW 2024 onwards 2E Continue to improve management and sharing of GIS datasets, including flood records, drainage assets, watercourse information and completed improvement works. New WDC and ScW 2024 onwards Develop a strategic understanding of sewer 3A Align future flood risk management activities and investment decisions with the Dalmuir System Plan. New WDC and ScW 2026 onwards
Page 95
Clydebank Surface Water Management Plan_For Submission 07_26 TBC 1.0 | 16th July 2026 95 AtkinsRéalis - Baseline / Référence and surface water interactions 3B Investigate opportunities to reduce runoff entering the combined sewer network through retrofit SuDS, blue-green infrastructure, source control and surface water separation projects. New WDC and ScW 2026 onwards Improve understanding of flood risk at Second Avenue / Ramsay Street 4A Coordinate with ScW to share information to help develop an improved understanding of flood risk at Second Avenue and the best solution to pursue. New WDC / ScW 2024 onwards Reduce Surface Water flood risk at Second Avenue 4B Collaborate with ScW to realise any potential shared interests and funding opportunities. New WDC 2024 onwards* Improve understanding of flood risk at Western Isles Road 5A Coordinate with ScW to share information to help develop an improved understanding of flood risk at Western Isles Road and the best solution to pursue. The existing sewer system appears to be undersized so this should be considered. New WDC / ScW 2024 onwards Reduce Surface Water flood risk at Western Isles Road 5B Collaborate with ScW to realise any potential shared interests and funding opportunities. New WDC 2024 onwards* Improve understanding of flood risk at Duntocher Road 6A Review flood risk and potential interventions following completion of ScW investigations into the unnamed watercourse, sewer connectivity and wider drainage interactions. New WDC / ScW 2024 onwards Reduce Surface Water flood risk at Duntocher Road 6B Collaborate with ScW to realise any potential shared interests and funding opportunities. New WDC 2024 onwards* Improve understanding of flood risk at Livingstone Street 7A Review flood mechanisms and potential interventions following completion of ScW investigations into historic watercourse interactions and sewer network performance. New WDC / ScW 2024 onwards Reduce Surface Water flood risk at Livingstone Street 7B Collaborate with ScW to realise any potential shared interests and funding opportunities. New WDC 2024 onwards* Improved understanding of flood risk at Melbourne Avenue 8A Continue collaboration with ScW to improve understanding of sewer exceedance and identify opportunities to reduce flood risk through integrated drainage management. New WDC / ScW 2024 onwards
Page 96
Clydebank Surface Water Management Plan_For Submission 07_26 TBC 1.0 | 16th July 2026 96 AtkinsRéalis - Baseline / Référence Reduce Surface Water flood risk at Melbourne Avenue 8B Collaborate with ScW to realise any potential shared interests and funding opportunities. New WDC 2024 onwards* Reduce stress on existing combined sewer where possible when considering new development proposals, retrofit schemes, resurfacing works etc. 9A To support the Dalmuir System Plan, find ways to increase capacity in the existing combined sewer in the Clydebank area by removing surface water from this system. For example, retrofitting SuDS, underground storage areas or creating a separated surface water pipe system. This will have a greater impact where closer to the flooding area. New WDC 2024 onwards* Continue working with ScW to manage internal and external sewer flooding 10A Make sure all incidents of external and internal flooding of properties and infrastructure are reported. This will keep record up to date and help understand future flooding. New WDC 2024 onwards 10B Make sure that following an incident of sewer flooding (internal or external) that an appropriate clean-up is undertaken. New WDC / ScW 2024 onwards* 10C Make sure that a thorough investigation into the likely causes of sewer flooding (both internal and external) take place. Homeowners and business owners should be informed New WDC / ScW 2024 onwards* Future option development 11A Reassess the options developed as part of the original SWMP following completion of key stakeholder investigations and any future model updates New WDC / ScW 2026 onwards 11B Develop future options as part of a collaborative catchment-wide strategy rather than isolated hotspot-specific schemes. New WDC / ScW 2026 onwards *Subject to funding availability
Page 97
AtkinsRéalis - Baseline / Référence AtkinsRéalis UK Limited Stamp Office 10 Waterloo Place Edinburgh EH1 3EG © AtkinsRéalis UK Limited except where stated otherwise