(b) Planning Decision Notice, Report of Handling and Reference Documents (Pages 679-718)
Perth and Kinross Council · 11 November 2024
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4(iii)(b) LRB-2024-40 LRB-2024-40 23/01610/FLL – Demolition of buildings and erection of 3 agricultural buildings, formation of hardstanding and associated works, The Castle Farm, Methven, Perth, PH1 3SU PLANNING DECISION NOTICE REPORT OF HANDLING REFERENCE DOCUMENTS (part included in applicant’s submission, pages 261-378, 416-421, 426 and 431-653)
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H C Pilkington Trust C/O Savills Earn house Perth PH1 1RA METHVEN CASTLE FARM – NEW STEADINGS DRAINAGE IMPACT ASSESSMENT (DIA) DRAINAGE STRATEGY REPORT Report Ref. 603513-REP-0001-02 Date 1st November 2023 Allen Gordon LLP Saltire House Whitefriars Business Park Perth PH2 0PA t. 01738 639881 e. perth@allengordon.co.uk
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 2 01.11.2023 Issue and Revision Record Rev Date Originated Checked Approved Description 01 17.01.2023 AGC GJD GJD First issue 02 01.11.2023 AGC GJD GJD Plans and FEH13 updated Saltire House Whitefriars Business Park Perth PH2 0PA 8 Ardross Street Inverness IV3 5NN Springfield House Laurelhill Business Park Stirling FK7 9JQ t. (01738) 639881 t. (01463) 236516 t. (01786) 406576 e. perth@allengordon.co.uk e. inverness@allengordon.co.uk e. stirling@allengordon.co.uk This document has been prepared for the titled project or named part thereof and may not be relied upon or used in relation to any other project without the prior written authority of Allen Gordon LLP. Allen Gordon accept no responsibility or liability for any consequences of this document being used for a purpose other than the purposes for which it was commissioned. Any person using or relying upon the document for such other purpose agrees, and will by such use or reliance be deemed to have agreed, to indemnify Allen Gordon for any and all resulting loss or damage. Allen Gordon accept no responsibility or liability for this document to any party other than the person by whom it was commissioned. No alterations may be made to this report without the prior approval of Allen Gordon.
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 3 01.11.2023 Contents 1. Introduction .............................................................................................................................. 4 2. Site Details ................................................................................................................................ 4 3. Existing Drainage ....................................................................................................................... 4 4. Proposed Drainage Arrangements ............................................................................................. 4 5. Hydrological Characteristics ....................................................................................................... 5 6. Greenfield Runoff Rate Analysis ................................................................................................. 5 7. SUDS Water Quality ................................................................................................................... 6 8. Detention Basin – Construction ................................................................................................. 7 9. Swales ....................................................................................................................................... 9 10. SUDS Adoption ........................................................................................................................ 11 11. Conclusions and Recommendations ......................................................................................... 12 12. Appendices .............................................................................................................................. 13 Tables Table 1 - Hydrological Catchment Characteristics .................................................................................. 5 Table 2 - Greenfield Runoff Rates ......................................................................................................... 6 Table 3 - Detention Basin Operation and Maintenance Requirements ................................................... 9 Table 4- Swale Operation and Maintenance Requirements ................................................................. 11 Appendix Appendix A: Existing Site Plan Appendix B: Proposed Drainage Layout Plan Appendix C: Micro Drainage Network Calculations Appendix D: Greenfield Runoff Rates Appendix E: Treatment Volume Calculation (Vt) Appendix F: SEPA’s Simple Index Approach (SIA) Calculation
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 4 01.11.2023 1. Introduction Allen Gordon LLP have been commissioned to undertake a drainage impact assessment (DIA) for a proposed new steading at Methven Castle Farm. The assessment will describe the surface water drainage arrangements for the proposed steading and will assess the impact on existing drainage systems and the water environment. The assessment is intended to support a planning application to Perth & Kinross Council. A copy of the Site Layout Plan is included in Appendix A. 2. Site Details The proposed site is approximately 600m northeast of the A85 on the eastern edge of Methven (OS grid reference NO 04310 26150). The site rises south to north from approximately 75.0m AOD to around 90.5m AOD. The proposed site is in a rural setting with a scattering of dwellings surrounding the site. There are existing dilapidated buildings occupying the site which are to be demolished and replaced by high quality agricultural buildings. A copy of the Existing Site Plan is presented in Appendix A. 3. Existing Drainage Little is known about the existing surface water disposal arrangements for the existing buildings, although is believed they are directed to local soakaways which, given the age of the buildings, will not comply with current standards. There is a ditch to the south of the site where surface water from the proposed steading could be disposed of at restricted greenfield runoff rates. The watercourse channel appears to be small suggesting that it serves a small, local catchment. The watercourse is not included in the SEPA Water Classification online hub for water bodies. For the purposes of this report, the water quality in the ditch will be categorised as ‘good’. 4. Proposed Drainage Arrangements A copy of the proposed drainage plan is included in Appendix B. The following statements provide additional information on the individual SUDS elements:- • Runoff from the roof of the main steading will be directed to adequately sized rainwater pipes. Once below ground, flows will be piped by gravity to a proposed SUDS basin. A number of silt trap chambers will be strategically located around the building to provide pre-treatment. • A SUDS basin is proposed to the south of the steading. The basin will be sized to provide adequate attenuation and treatment. The discharge rate from the basin will be controlled. • The SUDS basin will discharge to a swale for further attenuation and treatment before discharge to the receiving ditch. A series of check dams will be provided across the swale to increase storage and control the discharge rate. • An analysis flow in the swale will be required at the detailed design stage. There may be a requirement to use energy dissipation measures where flow velocities in the swale have the potential to lead to scouring.
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 5 01.11.2023 For the purposes of the planning stage design, it has been assumed that no infiltration will occur from the basin or swale. From data provided by the British Geological Survey, the native soil on the site is anticipated to be glacial till, which is likely to exhibit moderate to poor permeability. Nonetheless, some infiltration will occur. Soil testing at the detailed design test could be used to evaluate the permeability which may allow the design to be refined. As a guide, The SUDS Manual (CIRIA C753, 2015) suggests that a permeability rate of 3x10-7 m/s would be a reasonable estimate for glacial till. This would be sufficient to provide some interception infiltration for all surfaces. Analysis of the main SUDS basin was carried out in Micro Drainage using a 35% allowance for climate change. Note that additional flow control will be required within the swale to further reduce the slightly elevated discharge rate adopted for the SUDS basin. A copy of the Micro Drainage calculation is included in Appendix C. 5. Hydrological Characteristics The hydrological catchment characteristics for the site which have been used in the hydraulic design of the surface water system, including SUDS components, are presented below in Table 1. Table 1 - Hydrological Catchment Characteristics Parameter Value SAAR 839 mm SOIL factor 0.37 M5–60 17.0 mm Ratio r 0.3 Hydrological region 1 In order to mimic the existing natural surface water environment, all new developments are required to take account of the quantity and quality of surface water runoff. Guidance on best practice and design requirements are given in The SUDS Manual (CIRIA C753). 6. Greenfield Runoff Rate Analysis Equation 24.3 (IH124 catchment description equation) from CIRIA 753 was used to calculate greenfield runoff rates. The site area has been restricted to the footprint of the proposed steading and concrete hard standing areas, taken as 0.26 hectares. A copy of the calculation is included in Appendices D. As the site is less than 50ha, the formula is applied for 50ha and the result factored based on the ratio of the two areas. To get the 1 to 200 year throttle rates, the FSR growth curve for Hydrological Region 1 is required (as set out in FSSR14). Adopting this approach, the greenfield runoff rates are as displayed in Table 2.
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 6 01.11.2023 Table 2 - Greenfield Runoff Rates Flow rate Value QBAR for 50 ha 3.6 l/s/ha Q1 yr. 0.8 l/s Q2 yr. 0.8 l/s Q30 yr. 1.7 l/s Q100 yr. 2.3 l/s Q200 yr. 2.6 l/s A Hydrobrake® flow control device is proposed to control discharge flows from the SUDS basin. The risk of blockage of the orifice has been categorised as moderate to high and in line with industry standards the Hydrobrake® orifice opening will be no less than 75mm in diameter. The minimum flow rate for a Hydrobrake® orifice diameter of 75mm is 2.5 l/s at a head of 1.0m (calculated using Micro Drainage Source Control module and applying the upstream storage depth as the governing selection criterion). The flow rate from the SUDS basin would normally be limited to QBAR divided by the catchment area. Using this approach, the discharge from the SUDS basin would be restricted to approximately 1.0l/s. The proposed figure of 2.5 l/s is significantly higher but still lower than the greenfield runoff rate for the 1 in 200 year return period storm. As above, further flow control will be required in the second SUDS stage i.e. the swale. The possible forms of flow control in the swale should be assessed at the detailed design stage. Control weirs or orifice plates at the check dams are possible solutions. 7. SUDS Water Quality Calculation of the water quality volume has been carried out in accordance with CIRIA C753 Equation 23.1, “Vt calculation using variable rainfall depths for Scotland”. The calculation returned a treatment volume for the SUDS basin of 40m3. Note that the required long-term storage when flows are restricted is just over 159m3 i.e. almost four times the minimum treatment volume. A copy of the calculation is included in Appendix D. SEPA’s Simple Index Approach is a simplified risk-based method for selecting appropriate sustainable drainage systems (SUDS) for the treatment of surface water runoff. The approach, as outlined in CIRIA C753, assigns pollution hazard indices based on land use. The contaminants considered are total suspended solids (TSS), metals and hydrocarbons. Suitable SUDS features are then selected to achieve a combined mitigation index greater than the pollution hazard index, indicating that the pollution risk has been appropriately managed.
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 7 01.11.2023 The proposed roof runoff has been categorised as medium risk of metal leaching and requires, in addition to a detention basin, an extra level of treatment to further reduce metals. As set out in Section 4, it is proposed to introduce a swale to further enhance the treatment and reduce the metals content. It should be noted that the swale will need regular check dams to increase the storage capacity and control flow rates. A copy of the calculation is included in Appendix E. 8. Detention Basin – Construction The bottom and side slopes of the basin should be carefully prepared to ensure that they are structurally stable and the grading should be uniform and smooth to the correct slope so that water does not pond in depressions and the risk of channelling and erosion through preferential flow paths is minimised. Checks should be made that any embankment structures meet their design criteria. The preparation should also ensure that the basin will satisfactorily manage design flows without significant erosion damage. Backfilling against inlet and outlet structures needs to be controlled so as to minimise settlement and erosion. The soils used to finish the side slopes need to be suitably fertile, porous and of sufficient depth to ensure healthy vegetation growth. Where an impermeable liner is proposed, care should be taken to ensure that it is not damaged during construction. During the SUDS establishment phase, runoff from bare soils should be minimised. For example: • Vegetation on slopes should be rapidly established. • Base-of-slope trenches should be introduced to retain the inevitable runoff of sediments. • As far as practicable, construction should be timed to avoid autumn and winter when high runoff rates are to be expected. Detention basins may be used to manage construction runoff and trap construction sediments, provided they are fully rehabilitated to original design formation levels before handover. Detention Basin Operation and Maintenance Requirements 8.5.1. Detention basins will require ongoing regular maintenance to ensure continuing operation to design performance standards. 8.5.2. Maintenance of detention basins is relatively straightforward for landscape contractors, and typically there should only be a small amount of extra work (if any) required for a SUDS detention basin over and above what is necessary for standard public open space. 8.5.3. Maintenance responsibility for a basin should always be placed with an appropriate organisation. Adequate access should be provided to all detention basin areas for inspection and maintenance, including for appropriate equipment and vehicles. Litter and debris removal should be undertaken as part of general landscape maintenance for the site. All litter should be removed from site. 8.5.4. The major maintenance requirement for detention basins is usually mowing. Regular mowing in and around detention basins is only required along maintenance access routes, amenity areas (e.g. footpaths), across any embankment and across the main
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 8 01.11.2023 storage area. The remaining areas can be managed as "meadow", unless additional management is required for landscape/amenity/recreational or aesthetic reasons. 8.5.5. Mowing should ideally retain grass lengths of 75-150 mm across the main "treatment" surface to assist in filtering pollutants and retaining sediments and to reduce the risk of flattening during runoff events. Longer lengths of vegetation may be appropriate, depending on the functionality of the component, and its associated design criteria and are not considered to pose a significant risk to functionality. 8.5.6. Shorter lengths may be required when recreational facilities form part of the basin, but in this case the basin will be dealing with exceedance flows only and not treatment. 8.5.7. Grass clippings should be disposed of off-site or outside the detention basin area to remove nutrients and pollutants. Where a detention basin has a small permanent pool at the outlet, its submerged and emergent aquatic vegetation should be managed as for ponds or wetlands. Plant management, to achieve the desired habitat effect, should be clearly specified in a maintenance schedule. All vegetation management activities should take account of the need to maximise biosecurity and prevent the spread of invasive species. 8.5.8. Occasionally sediment will need to be removed (e.g. once deposits exceed 25 mm in depth). Sediments excavated from a detention basin that receives runoff from residential or standard road and roof areas are generally not toxic or hazardous and can therefore be safely disposed of by either land application or landfilling. However, consultation should take place with the environmental regulator to confirm appropriate protocols. Sediment testing may be required before sediment excavation to determine its classification and appropriate disposal methods. For runoff from busy streets with high vehicle traffic, sediment testing will be essential. In the majority of cases, it will be acceptable to distribute the sediment on-site if there is an appropriate safe and acceptable location to do so. Any damage due to sediment removal or erosion and scour resulting from major events should be repaired and immediately reseeded or planted. 8.5.9. Table 4 provides guidance on the type of operational and maintenance requirements that may be appropriate. The list of actions is not exhaustive and some actions may not always be required.
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 9 01.11.2023 Table 3 - Detention Basin Operation and Maintenance Requirements Maintenance schedule Required action Typical frequency Regular maintenance Remove litter (including leaf litter) and debris. Cut grass - for spillways and access routes. Cut grass - meadow grass in and around basin Manage other vegetation and remove nuisance plants. Remove sediment from pre-treatment devices. Inspect inlets, outlets and overflows for blockages, and clear if required. Inspect banksides, structures, pipework etc for evidence of physical damage Check any penstocks and other mechanical devices and tidy all dead growth before start of growing season. Monthly (or as required) Monthly (during growing season, as required) Half yearly (spring - before nesting season, and autumn) Six monthly Bi-monthly Six monthly or as required. Yearly Occasional maintenance Remove or control tree roots where they are encroaching the sides of the basin, using recommended methods (e.g. NJUG, 2007 or BS 3998:2010). Prune and trim any trees and remove cuttings. Clear pipework/channel blockages. Reseed areas of poor vegetation growth. As required As required As required Remedial actions Repair erosion or other damage by reseeding or re- turfing. Realignment of rip-rap. Repair/rehabilitation of inlets, outlets and overflows. Relevel uneven surfaces and reinstate design levels. As required As required As required As required 9. Swales The bottom and side slopes of the swale should be carefully prepared to ensure that they are sound, uniform and smooth. Checks should be made that any side slopes meet their design criteria. The preparation should also ensure that the swale will satisfactorily manage the design flows without significant erosion damage. Backfilling against inlet and outlet structures needs to be controlled so as to minimise settlement and erosion. The soils used to finish the side slopes need to be suitably fertile, porous and of sufficient depth to ensure healthy vegetation growth. During the SUDS establishment phase, runoff from bare soils should be minimised. For example: • Vegetation on slopes should be rapidly established. • Base-of-slope trenches should be introduced to retain the inevitable runoff of sediments. • As far as practicable, construction should be timed to avoid autumn and winter when high runoff rates are to be expected.
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 10 01.11.2023 The swales may be used to manage construction runoff and trap construction sediments, provided they are fully rehabilitated to original design formation levels before handover. Operation and Maintenance Requirements 9.5.1. The swales will require ongoing regular maintenance to ensure that they continue to operate as designed. 9.5.2. Maintenance of swales is relatively straightforward for landscape contractors, and typically there should only be a small amount of extra work (if any) required for a SUDS swale over and above what is necessary for standard public open space. 9.5.3. Maintenance responsibility for a swale should always be placed with an appropriate organisation. Adequate access should be provided to all areas surrounding swales for inspection and maintenance, including for appropriate equipment and vehicles. Litter and debris removal should be undertaken as part of general landscape maintenance for the site. All litter should be removed from site. 9.5.4. The major maintenance requirement for swales is usually mowing. Regular mowing in and around the swales is only required along maintenance access routes, amenity areas (e.g. footpaths), across the side slopes and along the main storage channel. The remaining areas can be managed as "meadow", unless additional management is required for landscape/amenity/recreational or aesthetic reasons. 9.5.5. Mowing should ideally retain grass lengths of 75-150mm across the main "treatment" surface to assist in filtering pollutants and retaining sediments and to reduce the risk of flattening during runoff events. 9.5.6. Grass clippings should be disposed of off-site or outside the swale area to remove nutrients and pollutants. 9.5.7. Occasionally sediment will need to be removed (e.g. once deposits exceed 25mm in depth). Sediments excavated from a swale that receives runoff from residential road and roof areas are generally not toxic or hazardous and can therefore be safely disposed of by either land application or landfilling. However, consultation should take place with the environmental regulator to confirm appropriate protocols. Sediment testing may be required before sediment excavation to determine its classification and appropriate disposal methods. In the majority of cases, it will generally be acceptable to distribute the sediment on-site if there is an appropriate safe and acceptable location to do so. Any damage due to sediment removal or erosion and scour resulting from major events should be repaired and immediately reseeded or planted. 9.5.8. Table 7 provides guidance on the type of operational and maintenance requirements that may be appropriate. The list of actions is not exhaustive and some actions may not always be required.
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 11 01.11.2023 Table 4- Swale Operation and Maintenance Requirements Maintenance schedule Required action Typical frequency Regular maintenance Remove litter (including leaf litter) and debris. Cut grass - for side slopes and channel. Cut grass - meadow grass in and around swale Manage other vegetation and remove nuisance plants. Remove sediment from pre-treatment devices. Inspect inlets, outlets and overflows for blockages, and clear if required. Monthly (or as required) Monthly (during growing season, as required) Half yearly (spring - before nesting season, and autumn) Six monthly Bi-monthly Occasional maintenance Remove or control tree roots where they are encroaching the sides of the swale, using recommended methods (e.g. NJUG, 2007 or BS 3998:2010). Prune and trim any trees and remove cuttings. Clear pipework/channel blockages. Reseed areas of poor vegetation growth. As required As required As required Remedial actions Repair erosion or other damage by reseeding or re- turfing. Realignment of rip-rap. Repair/rehabilitation of inlets, outlets and overflows. Relevel uneven surfaces and reinstate design levels. As required As required As required As required 10. SUDS Adoption The SUDS basin will only be serving a single commercial property and as such Perth & Kinross Council (PKC) would not consider it for adoption and it will remain private. The owners will be responsible for the routine SUDS maintenance.
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 12 01.11.2023 11. Conclusions and Recommendations The proposed drainage arrangements comprising a SUDS detention basin with a minimum storage volume of 174.3m3 and swale would appear to satisfy the requirements for SUDS treatment. Outflow from the basin will be restricted to rate close to the greenfield runoff rate for the 1 in 200 year return period. The discharge from the proposed SUDS basin has been restricted to 2.5 l/s. This assumes a Hydrobrake® orifice of 75mm and a design head of 1.0 metres. A 75mm minimum orifice has been adopted in line with industry standards where the risk of blockages is categorised as high. The potential to include interception infiltration should be investigated at the detailed design stage. This will need in-situ testing of soil permeability and may allow the design to be refined. A technical assessment of the swale arrangement will be required at detailed design stage to further reduce discharge flow rates.
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Page 13 01.11.2023 12. Appendices
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Appendix 01.11.2023 Appendix A: Existing Site Plan
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80 160 240 320 4000 This document and its design content is copyright © and is the property of Savills. It may not be reproduced without their expressed permission. It shall be read in conjunction with all other associated project information including models, specifications, schedules and related consultants drawings and documentation. Do not scale from this drawing unless for Planning purposes. Figured dimensions only are to be used. All dimensions must be checked on site by the Contractor prior to the commencement of any fabrication or building works. Immediately report any discrepancies, errors or omissions to Savills prior to the commencement of any fabrication or building works. If in doubt please ASK. NOTES REVISIONS CLIENT PROJECT TITLE CHECKED BY DATE PROJECT / DWG / REV NO.SCALES @ A3 DRAWING STATUS DRAWN BY DRAWING TITLE PILKINGTON TRUST LOCATION PLAN Earn House Broxden Business Park Lamberkine Drive Perth, PH1 1RA t: 01738 477528 f: 01738 445599 FARM RATIONALISATION METHVEN CASTLE FARM, METHVEN PERTH, PH1 3SU PLANNING 1:2500 DHBU393113-01 A CR - 01-05-23 Location Plan 1:2500 A3 Ordnance Survey (c) Crown Copyright 2017. All rights reserved. Licence number 100022432 APPLICANT OWNERSHIP BLUE EXTENTS NN A86 TO LOCHTY & PERTH A86 TO METHVEN NON DEVELOPMENT SITE ACCESS REV DATENOTE / DRAWN BY REV:A:NON DEVELOPMENT SITE ACCESS ADDED 14-06-23
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Appendix 01.11.2023 Appendix B: Proposed Drainage Layout Plan
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Cottage Farm 5 Methven Castle 4 Issues Castle Farm Cottage Pepperwell Castle Kineel 371m² 255m² Existing farm sheds to be retained STC STC STC IC IC Existing culvert > Existing burn > Inlet Outlet SUDS basin 174.3m³ Proposed access track FC 225Ø @ 1:100 > 225Ø @ 1:100 > 300Ø @1:100 > 814m² 847m² 692m² DRAWN CHECKED APPROVED DATE DATE DATE DRAWING No. SCALES STATUS AT SHEET SIZE C Allen Gordon LLP 2019 A1 20/09/2022 EH 603513-DRG-0002-0B 1:500 CLIENT PROJECT TITLE METHVEN CASTLE STEADING PROPOSED SUDS ARRANGEMENT SUITE 3, SALTIRE HOUSE WHITEFRIARS BUSINESS PARK PERTH PH2 0PA Tel 01738 639881 e-mail : perth@allengordon.co.uk 8 ARDROSS STREET INVERNESS IV3 5NN Tel 01463 236516/233471 Fax 01463 711767 e-mail : inverness@allengordon.co.uk 2/5 & 2/6 SPRINGFIELD HOUSE LAURELHILL BUSINESS PARK STIRLING FK7 9JQ Tel 01786 406576 e-mail : stirling@allengordon.co.uk CONSULTING CIVIL AND STRUCTURAL ENGINEERS KEY STC SILT TRAP CHAMBER IC INSPECTION CHAMBER FC FLOW CONTROL CHAMBER AllenGordon SAVILLS 16/01/2023 AGC REV DRAWN CHK'D APPR'D DATEDESCRIPTION 0A EH AGC GD 17.01.23ISSUED FOR PLANNING FOR PLANNING 200 10 SCALE 1:500 METRES 30 40 50 17/01/2023 GD 0B EH AGC GD 31.10.23BUILDING FOOTPRINT MOVED
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Appendix 01.11.2023 Appendix C: Micro Drainage Network Calculations
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Allen Go rdon LLP Page 1 Suite 3, Saltire House Whitefriars Business Park Perth PH2 0PA Methven Castle Farm New Steading 603513-CAL-0004-02 Date 19/08/2022 File 603513-CAL-0004-02 FEH22... Designed by AGC Checked by GD Innovyze Source Control 2020.1.3 Summary of Results for 200 year Return Period (+39%) Storm Max Max Max Max Max Max Status Event Level Depth Control Overflow Σ Outflow Volume (m) (m) (l/s) (l/s) (l/s) (m³) 15 min Summer 88.461 0.461 2.5 0.0 2.5 63.2 O K 30 min Summer 88.592 0.592 2.5 0.0 2.5 87.0 O K 60 min Summer 88.706 0.706 2.5 0.0 2.5 110.3 Flood Risk 120 min Summer 88.771 0.771 2.5 0.0 2.5 124.5 Flood Risk 180 min Summer 88.808 0.808 2.5 0.0 2.5 132.9 Flood Risk 240 min Summer 88.832 0.832 2.5 0.0 2.5 138.6 Flood Risk 360 min Summer 88.860 0.860 2.5 0.0 2.5 145.3 Flood Risk 480 min Summer 88.871 0.871 2.5 0.0 2.5 148.0 Flood Risk 600 min Summer 88.875 0.875 2.5 0.0 2.5 149.0 Flood Risk 720 min Summer 88.877 0.877 2.5 0.0 2.5 149.3 Flood Risk 960 min Summer 88.873 0.873 2.5 0.0 2.5 148.5 Flood Risk 1440 min Summer 88.854 0.854 2.5 0.0 2.5 143.9 Flood Risk 15 min Winter 88.506 0.506 2.5 0.0 2.5 71.0 O K 30 min Winter 88.648 0.648 2.5 0.0 2.5 98.0 O K 60 min Winter 88.770 0.770 2.5 0.0 2.5 124.3 Flood Risk 120 min Winter 88.842 0.842 2.5 0.0 2.5 141.0 Flood Risk 180 min Winter 88.885 0.885 2.5 0.0 2.5 151.3 Flood Risk 240 min Winter 88.913 0.913 2.5 0.0 2.5 158.5 Flood Risk 360 min Winter 88.949 0.949 2.5 0.0 2.5 167.7 Flood Risk Storm Rain Flooded Discharge Overflow Time-Peak Event (mm/hr) Volume Volume Volume (mins) (m³) (m³) (m³) 15 min Summer 134.415 0.0 65.2 0.0 22 30 min Summer 93.308 0.0 90.5 0.0 36 60 min Summer 60.281 0.0 117.4 0.0 66 120 min Summer 35.579 0.0 138.6 0.0 124 180 min Summer 26.408 0.0 154.3 0.0 184 240 min Summer 21.478 0.0 167.3 0.0 242 360 min Summer 16.159 0.0 188.8 0.0 362 480 min Summer 13.238 0.0 206.2 0.0 476 600 min Summer 11.343 0.0 220.9 0.0 528 720 min Summer 9.997 0.0 233.6 0.0 594 960 min Summer 8.177 0.0 254.7 0.0 724 1440 min Summer 6.124 0.0 286.0 0.0 996 15 min Winter 134.415 0.0 73.0 0.0 22 30 min Winter 93.308 0.0 101.4 0.0 36 60 min Winter 60.281 0.0 131.5 0.0 64 120 min Winter 35.579 0.0 155.2 0.0 122 180 min Winter 26.408 0.0 172.8 0.0 180 240 min Winter 21.478 0.0 187.4 0.0 238 360 min Winter 16.159 0.0 211.5 0.0 352 ©1982-2020 Innovyze
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Allen Gordon LLP Page 2 Suite 3, Saltire House Whitefriars Business Park Perth PH2 0PA Methven Castle Farm New Steading 603513-CAL-0004-02 Date 19/08/2022 File 603513-CAL-0004-02 FEH22... Designed by AGC Checked by GD Innovyze Source Control 2020.1.3 Summary of Results for 200 year Return Period (+39%) Storm Max Max Max Max Max Max Status Event Level Depth Control Overflow Σ Outflow Volume (m) (m) (l/s) (l/s) (l/s) (m³) 480 min Winter 88.967 0.967 2.5 0.0 2.5 172.4 Flood Risk 600 min Winter 88.974 0.974 2.5 0.0 2.5 174.3 Flood Risk 720 min Winter 88.975 0.975 2.5 0.0 2.5 174.3 Flood Risk 960 min Winter 88.968 0.968 2.5 0.0 2.5 172.6 Flood Risk 1440 min Winter 88.940 0.940 2.5 0.0 2.5 165.4 Flood Risk Storm Rain Flooded Discharge Overflow Time-Peak Event (mm/hr) Volume Volume Volume (mins) (m³) (m³) (m³) 480 min Winter 13.238 0.0 231.0 0.0 464 600 min Winter 11.343 0.0 247.4 0.0 570 720 min Winter 9.997 0.0 261.6 0.0 672 960 min Winter 8.177 0.0 285.3 0.0 762 1440 min Winter 6.124 0.0 320.1 0.0 1072 ©1982-2020 Innovyze
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Allen Gordon LLP Page 3 Suite 3, Saltire House Whitefriars Business Park Perth PH2 0PA Methven Castle Farm New Steading 603513-CAL-0004-02 Date 19/08/2022 File 603513-CAL-0004-02 FEH22... Designed by AGC Checked by GD Innovyze Source Control 2020.1.3 Rainfall Details Rainfall Model FEH Return Period (years) 200 FEH Rainfall Version 2022 Site Location GB 304550 725750 NO 04550 25750 Data Type Catchment Summer Storms Yes Winter Storms Yes Cv (Summer) 0.750 Cv (Winter) 0.840 Shortest Storm (mins) 15 Longest Storm (mins) 1440 Climate Change % +39 Time Area Diagram Total Area (ha) 0.260 Time (mins) Area Time (mins) Area From: To: (ha) From: To: (ha) 0 4 0.173 4 8 0.087 ©1982-2020 Innovyze
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Allen Gordon LLP Page 4 Suite 3, Saltire House Whitefriars Business Park Perth PH2 0PA Methven Castle Farm New Steading 603513-CAL-0004-02 Date 19/08/2022 File 603513-CAL-0004-02 FEH22... Designed by AGC Checked by GD Innovyze Source Control 2020.1.3 Model Details Storage is Online Cover Level (m) 89.000 Tank or Pond Structure Invert Level (m) 88.000 Depth (m) Area (m²) Depth (m) Area (m²) 0.000 105.0 1.000 270.0 Hydro-Brake® Optimum Outflow Control Unit Reference MD-SHE-0075-2500-1000-2500 Design Head (m) 1.000 Design Flow (l/s) 2.5 Flush-Flo™ Calculated Objective Minimise upstream storage Application Surface Sump Available Yes Diameter (mm) 75 Invert Level (m) 88.000 Minimum Outlet Pipe Diameter (mm) 100 Suggested Manhole Diameter (mm) 1200 Control Points Head (m) Flow (l/s) Control Points Head (m) Flow (l/s) Design Point (Calculated) 1.000 2.5 Kick-Flo® 0.627 2.0 Flush- Flo™ 0.307 2.5 Mean Flow over Head Range - 2.2 The hydrological calculations have been based on the Head/Discharge relationship for the Hydro-Brake® Optimum as specified. Should another type of control device other than a Hydro-Brake Optimum® be utilised then these storage routing calculations will be invalidated Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s) 0.100 2.1 1.200 2.7 3.000 4.1 7.000 6.2 0.200 2.4 1.400 2.9 3.500 4.5 7.500 6.4 0.300 2.5 1.600 3.1 4.000 4.7 8.000 6.6 0.400 2.5 1.800 3.3 4.500 5.0 8.500 6.8 0.500 2.4 2.000 3.4 5.000 5.3 9.000 7.0 0.600 2.1 2.200 3.6 5.500 5.5 9.500 7.1 0.800 2.3 2.400 3.7 6.000 5.7 1.000 2.5 2.600 3.9 6.500 6.0 ©1982-2020 Innovyze
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Allen Gordon LLP Page 5 Suite 3, Saltire House Whitefriars Business Park Perth PH2 0PA Methven Castle Farm New Steading 603513-CAL-0004-02 Date 19/08/2022 File 603513-CAL-0004-02 FEH22... Designed by AGC Checked by GD Innovyze Source Control 2020.1.3 Weir Overflow Control Discharge Coef 0.544 Width (m) 1.000 Invert Level (m) 89.000 ©1982-2020 Innovyze
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Appendix 01.11.2023 Appendix D: Greenfield Runoff Rates
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Appendix 01.11.2023 Appendix E: Treatment Volume Calculation (Vt)
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Methven Castle Farm – New Steadings Allen Gordon LLP Drainage Impact Assessment (DIA) 603513 Appendix 01.11.2023 Appendix F: SEPA’s Simple Index Approach (SIA) Calculation