Item 14 - Gruggies Burn Flood Alleviation Scheme (Revised Version)
West Dunbartonshire Council · 17 December 2025
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WEST DUNBARTONSHIRE COUNCIL Report by Chief Officer Roads and Neighbourhood West Dunbartonshire Council – 17 December 2025 Subject: Gruggies Burn Flood Alleviation Scheme 1. Purpose 1.1 The purpose of this report is to update members on the progress delivering the Gruggies Burn Flood Alleviation Scheme, advise of associated costs and confirm the Scottish Government funding position. 2. Recommendations 2.1 It is recommended that Council: i) Note that, following development of the detailed design, the costs of the Gruggies Burn Scheme have significantly increased since scheme conception in 2016. ii) Approve option 3 to construct coastal defences and flood gate as set out in paragraphs 4.27 to 4.32. This requires a total West Dunbartonshire capital investment of £2.94m which translates to a revenue impact of £0.137m per annum for a 40-year period to repay the loan and the incurred interest. iii) Note the funding milestone of 31 March 2026 for construction tender award. iv) Note that, should Option 2 or Option 3 be approved for delivery, the Council will liaise with the Scottish Government to confirm funding will be awarded for part implementation in advance of contract award. If the Scottish Government do not confirm positively a further report will be brought to Council. v) Authorise the Chief Officer Regulatory and Regeneration to conclude negotiations in relation to the finalisation and signing of the construction contract. vi) Grant delegated authority to Chief Officer Roads and Neighbourhood and Chief Officer Regulatory and Regeneration, in consultation with the Procurement Manager, to award any procurement and contract awards related to Gruggies Burn Flood Alleviation Scheme using appropriate procurement routes. ITEM 14 (Revised Version) Page 259
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3. Background 3.1 The Flood Risk Management (Scotland) Act 2009 established a modern framework for managing flood risk across Scotland. It aims to reduce the harmful effects of flooding on people, property and the environment through sustainable and coordinated planning. 3.2 The Flood Risk Management Act established three 6 year cycles of actions with the Scottish Government committing £420m of funding for schemes identified in Cycle 1. 42 schemes were identified across Scotland through this process with funding to be provided over a 10 year period. 3.3 West Dunbartonshire Council’s (the Council) Gruggies Burn Flood Alleviation project was one of the Cycle 1 schemes identified and prioritised through this process. 3.4 The Flood Risk Plan for Dumbarton was originally completed in 2012. One of the flood actions highlighted in that report was the development of a flood alleviation scheme for the Gruggies Burn. 3.5 The Gruggies Burn is an open watercourse approximately 1 mile long from the meeting of the Garshake and Overtoun Burns to the outfall on the estuary of the Clyde. It has steep fast moving culverted sections with 4 road crossings and 1 footpath crossing, with a tidally influenced outfall. Due to this the burn has two main historic flood paths – Fluvial (Watercourse) and Tidal. 3.6 Fluvial flooding occurs from the burn overspilling in periods of heavy rainfall but also overflowing in constrained culvert sections from Castlegreen Street to Glasgow Road. This can result in flooding of a number of properties in the Dumbarton East Area, including Castlegreen Street, Glasgow Road, Buchanan Street and the surrounding area. 3.7 Tidal flooding occurs from backwater effects from the Clyde during high tide or storm surge combined with a strong southwestern wind. This reduces discharge capacity and results in back up in the burn and overflowing upstream. 3.8 There are records of flooding from the burn causing minor temporary flooding going back to the 1950s including a few events recorded in the 1990s, with increasing reports in the 2000s. Since the late 2000s there has been an increase in precipitation levels which has resulted in more fluvial flooding from the burn, with reports of at least 1 flood event annually since 2002, the most significant being in 2007. 3.9 There are limited reports of significant impacts from tidal flooding alone, with most instances short lived and quickly dissipating as tide levels reduce. 3.10 Large scale flooding events occur during high tide or storm surge events combined with periods of heavy rainfall. This was last experienced in October 2023 with flooding to properties, businesses and significant disruption to the transport network. Page 260
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3.11 The initial scheme was developed and submitted to the Scottish Government for prioritisation and funding as part of the Cycle 1 funding. The scheme costs were expected to be £20m. At that stage however only high-level assessment and design had been undertaken. 3.12 All projects identified through this process were awarded grant funding of 80% of the scheme costs with the remaining 20% to be funded by the Local Authority. 3.13 The Gruggies Burn Flood Alleviation Scheme was awarded grant funding of £16m by the Scottish Government in 2016 as a Cycle 1 Scheme. A breakdown of the initial project costs and funding is shown below. Initial Project Funding £(m) Total Original Scheme Costs 20 West Dunbartonshire Council Funding (20%) 4 Scottish Government Funding (80%) 16 3.14 A large portion of Cycle 1 schemes in other councils as well as the Gruggies Burn Scheme reported significantly increased costs from their initial design. Consequently, the total funding available for all the Cycle 1 schemes was insufficient. The Scottish Government instructed a pause on all scheme progression in 2019 until funding levels could be reviewed and agreed. 3.15 Although progress was initially paused, in September 2021 the IRED Committee approved that Council capital funds be made available to continue to progress the detailed design of the scheme whilst awaiting a decision at national level. This has been progressed since that approval was granted. 3.16 The Scottish Government, after review, allowed projects to progress in 2022 however to ensure that Cycle 1 could be concluded placed several conditions on the projects identified. 3.17 As a result, all local authorities wishing to progress their projects had to: 1. Confirm their intention to undertake the works by October 2023. 2. Undertake all public consultation and notify the project by March 2024 3. Complete all design works and have the contract awarded by March 2026. Any local authority who fails to achieve any of the above targets would not be funded for the schemes identified. Page 261
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4. Main Issues 4.1 Committee approved our intention to progress the project in September 2021 and the Council undertook the required design and consultation works which allowed for the project to be notified to meet the deadline of 31st March 2024. 4.2 The Council also progressed the final detailed design to allow us to meet the final deadline of 31st March 2026 for tender award. 4.3 All design work has been delivered through the SCAPE Civil Engineering Framework by Balfour Beatty. Through undertaking the design works the Council have been able to regularly review costs and ensure ability for appointment of the construction contract in time to meet the required deadline. 4.4 Like many other projects identified in Cycle 1, the original estimated costs were based on a high-level assessment of the potential works involved. As detailed designs have progressed, the construction elements of the project have been assessed in more detail, and with more accurate estimates of the expected cost determined. 4.5 In addition to more clarity on the scale of works involved there has been a significant increase in construction costs including the impact of inflation. Additionally, the Scottish Environment Protection Agency now require schemes to factor in a 40% adjustment for the effects of climate change which has resulted in increased capacity requirements within the scheme. 4.6 The full project will include several key elements: 1. Installation of 4m wide diversion culvert from Strowans Well Road to outfall at Hunter Burn into the River Clyde 2. Construction of a new inlet structure to slow down the water and divert the water from the Gruggies Burn into the diversion culvert 3. Construction of new coastal defence walls 4. Coastal embankments 5. Flood gate 4.7 The cost to deliver the full scheme and all benefits is now estimated to be £44.7m. In addition to the construction costs this includes all preliminary site investigation and design works, all anticipated major utility service diversions and various ancillary works to facilitate the delivery of the project. 4.8 Although costs have increased significantly, the Council has been working with the designers to minimise construction costs. Through a value engineering exercise, which has included the implementation of an innovative hybrid high grade PVC/Concrete culvert approach, savings have been made. Page 262
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4.9 The Council will continue to explore any cost saving opportunities throughout the project stages. 4.10 The Scottish Government have been kept updated throughout the design process on the projected costs and the Council have been seeking assurances that the funding levels provided will remain at 80% of the overall costs at final tender stage rather than the original £20m estimate. 4.11 A letter provided by the Scottish Government on 5th November 2025 confirmed the agreed position is that the grant will be fixed at 80% of costs when the scheme costs are confirmed after tender stage. 4.12 The letter does highlight that, as the grant will be fixed at the final tender stage, should any additional costs exceed this value no additional grant is payable. A level of bias has been included in the predicted figures and tender process to accommodate a level of unforeseen risk. 4.13 As funding levels could not be confirmed and the potential increased costs to the Council were not clear, a phased construction approach was incorporated into the design so consideration could be given to partial installation should funding levels require. 4.14 Through this approach 4 options have been developed for members to consider. • Option 1 – Full Scheme Delivery • Option 2 – Delivery of Inlet and Diversion Culvert • Option 3 – Delivery of Coastal Defences and Flood Gates • Option 4 – Do Nothing 4.15 When considering the four options set out below Council should be mindful of the need to balance affordability and the delivery of flood prevention. The Council has one of the highest ratios of financing costs to net revenue of all 32 Scottish councils and material increases to the capital programme will have a consequential impact on the Council’s revenue budget gap in future years due to the loan charges associated with any borrowing. Option 1 would be broadly equivalent to a 1.0% increase in Council Tax. This is summarised in the Financial and Procurement Implications of this report at paragraph 6.1. Option 1 – Full Scheme Delivery 4.16 Option 1 is the full delivery of the scheme and will ensure the anticipated overall benefits for local residents are achieved, however with the requirement for 20% contribution of funding it requires the largest capital investment from the Council. 4.17 This would require a total capital investment of £8.94m from the Council, which is an additional £4.94m on the original value. Page 263
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4.18 Full scheme delivery provides the biggest reduction in flood risk to the area and delivers on the information provided to elected members and residents throughout the consultation process. 4.19 A cost benefit analysis for the full scheme highlights that 631 properties will benefit from reduced flood risk against fluvial (river) and pluvial (surface water) events. The whole life benefit cost for the full delivery of the project would be £70m. Overall the project provides a cost benefit ratio of 1.64. For a scheme to be considered to deliver a benefit a cost benefit ratio should be in excess of 1.0. 4.20 Option 1 – Full Scheme Capital Costs Summary £(m) West Dunbartonshire Council Funding (20%) 8.94 Scottish Government Funding (80%) 35.76 Total Scheme Costs 44.70 Option 2 – New Inlet and Diversion Culvert 4.21 The primary benefit of the scheme comes from the construction of the culvert and weir as the primary source of flooding is identified as watercourse and surface water flood risk. Option 2 allows for the delivery of the main benefits of the scheme but reduces the expected Council contribution. 4.22 This approach also ensures the Council maximises the opportunity for the local area from the available Scottish Government funding whilst leaving the smallest elements with the lower overall benefit to be delivered at a later stage should additional funding become available. 4.23 Of the two partial delivery options the construction of the culvert and weir provides the highest reduction in flood risk and addresses the most frequent flood issues in the Dumbarton area. 4.24 If progressing with this option, the Council would likely receive limited public negativity as it delivers the main objectives of the scheme and leaves the potential for the coastal elements to be delivered at a later date. 4.25 This option only reduces the number of properties benefiting by 5 to 626 properties. However, it should be noted these properties would only be protected against fluvial risk. 305 of the properties in the area would still be at risk of tidal flooding when tide levels are high. The whole life cost benefit for this option is £44m and the cost benefit ratio is 1.18. Page 264
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4.26 Option 2 – Construction of Culvert and Inlet Capital Cost Summary £(m) West Dunbartonshire Council Funding (20%) 7.84 Scottish Government Funding (80%) 31.36 Total Culvert Scheme Costs 39.20 Option 3 – Construction of Coastal Defences and Flood Gate Only 4.27 Coastal flooding in this area only occurs in periods of high tide when water levels in the burn are increased due to the volume of rainfall. In these circumstances although a proportion of properties are at risk of flooding, water levels can quickly dissipate as the tide level reduces. 4.28 This option provides the lowest overall benefit to the area. Full confirmation of Scottish Government funding is required in advance of the contract award for a phased implementation. 4.29 It is likely that progressing with this option alone may receive public criticism as it would fail to deliver on a significant portion of the scheme’s aims and objectives. As any Scottish Government funding in future years is likely to be focused on Cycle 2 delivery it is unlikely this scheme would receive further funding. 4.30 The delivery of option 3 will provide a benefit to 310 properties in total with this risk being restricted to tidal flooding only. There would be no benefit or protection provided for flooding resulting from heavy rain or capacity issues within the Gruggies Burn. 4.31 The cost benefit ratio is the highest at 2.05 due to the significant reduction in overall costs and has a whole life cost benefit of £26m. 4.32 Option 3 – Construction of Coastal Defences Capital Cost Summary £(m) West Dunbartonshire Council Funding (20%) 2.94 Scottish Government Funding (80%) 11.76 Total Original Scheme Costs 14.70 Option 4 - Do Nothing 4.33 Given the significant increase in the capital cost of the project since its inception and the consequential increase in the revenue costs (for example option 1 creating a revenue pressure of £0.419m per annum due to loan charges) the Council could decide not to proceed with the project. Page 265
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4.34 Under the terms of the Flood Risk Management Act (Scotland) the Council has various responsibilities in relation to mapping, evaluating, and maintaining our watercourses as well as developing flood risk management plans for the area. 4.35 The purpose of the Flood Risk Management Plan is to evaluate the current flood risk and identify potential interventions which could be introduced to reduce flood risk for that area. 4.36 Any cancellation of the project would require all capital expenditure incurred to date to be transferred to the revenue budget as there is no capital asset being created. The costs incurred to date are £1.98m which would need to be funded from Council reserves. 4.37 All consultations and notifications undertaken throughout the development of the scheme have set out the full delivery of the scheme. It is anticipated that the cancellation of the scheme would result in reputational damage to the Council. 4.38 Option 4 – Do Nothing Revenue Cost Summary £(m) West Dunbartonshire Council Funding (100%) 1.98 Total Costs Incurred to Date 1.98 4.39 Overall Option Summary Initial Estimate Option 1 Option 2 Option 3 Option 4 Total £20m £44.7m £39.2m £14.7m £1.98m West Dunbartonshire Council Contribution (20%) £4.0m £8.94m £7.84m £2.94m £1.98m Scottish Government Contribution (80%) £16.0m £35.76m £31.36m £11.76m N/A Whole Life Cost Benefit £70m £44m £26m N/A Cost Benefit Ratio 1.64 1.18 2.05 N/A Properties Protected 370 631 626 310 N/A The initial estimate was based on full delivery of the scheme in 2016. Page 266
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5. People Implications 5.1 There are no people implications associated with this proposal. 6. Financial and Procurement Implications 6.1 Taking account of the contributions anticipated from the Scottish Government the capital cost increase to the Council for full project delivery is £4.94m additional to the £4m in the original project scope. The borrowing requirement of £8.94m has an estimated revenue implication of £7.79m which will be spread over the life of the loan (at approximately £0.419m per annum – this estimate is based on a 40 year loan at 4.25% - this in indicative as the actual amount will depend on the interest rate when the borrowing occurs). The full costs to the Council of each of the four options is set out in the tables below CAPITAL Option 1 £m Option 2 £m Option 3 £m Option 4 £m WDC Contribution 8.94 7.84 2.94 N/A SG Contribution 35.76 31.26 11.76 N/A Total 44.70 39.10 14.70 N/A WDC REVENUE PER ANNUM Option 1 £m Option 2 £m Option 3 £m Option 4 £m Principal Repayment 0.224 0.196 0.074 N/A Interest on Principal 0.195 0.171 0.063 N/A Total 0.419 0.367 0.137 N/A WDC REVENUE 40 YEARS Option £m Option 2 £m Option 3 £m Option 4 £m Principal Repayment 8.94 7.84 2.94 N/A Interest on Principal 7.79 6.83 2.53 N/A Revenue in 25/26 0 0 0 1.98 Total 16.73 14.67 5.47 1.98 DIFFERENCE BETWEEN OPTION 1 AND OTHER OPTIONS Option 1 £m Option 2 £m Option 3 £m Option 4 £m Per Annum 0 -0.052 -0.282 N/A 40 Years 0 -2.059 -11.264 -14.749 6.2 All options will also require legal and procurement support to ensure the construction tender is awarded by 31 March 2026. Page 267
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7. Risk Analysis 7.1 There is a risk with any project of the size and complexity of increased construction costs due to unforeseen difficulties. Any delay to construction commencing may also increase costs due to rising material costs, however an element of risk has been built into the current costs. 7.2 Mitigation measures and value engineering of design options was undertaken before costs were refined, therefore reducing some risks related to cost increases. 7.3 The funding supplied by Scottish Government in fixed at 80% of the final tender package. If final costs are higher (for example through compensation events or contract variations) no additional funding is payable. Any additional costs will need to be funded directly by the Council. 7.4 The Scottish Government have advised that they are currently considering whether new affordability measures are necessary to bring the overall programme of Cycle 1 flood schemes within the available funding envelope. However, the only measure in place at this time is the 31 March 2026 milestone for any remaining schemes. 8. Equalities Impact Assessment (EIA) 8.1 A completed EIA was undertaken as part of the Detailed Design process and there have been no material changes in terms of impact on people with protected characteristics since. 9. Consultation 9.1 The detail contained within this report was considered by the Strategic Asset Management Group which is attended by representatives of all service areas. 10. Strategic Assessment 10.1 This report reflects the 2022 – 2027 Strategic Plan and in particular the following Strategic Priorities: • Our resources are used in an environmentally sustainable way • Our Council is adaptable and focused on delivering best value for our residents Chief Officer: Gail Macfarlane Service Area: Roads and Neighbourhood Date: 10 December 2025 Person to Contact: Liam Greene Roads and Transportation Manager Email: liam.greene@west-dunbarton.gov.uk Page 268
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Background Papers: IRED 15 September 2021 Gruggies Burn Flood Prevention Scheme Update IRED 2 November 2022 Flood Prevention Schemes - Levenhowe, River Leven and Gruggies Burn. Wards Affected: Dumbarton and Leven Wards Page 268A