Chapter 9: Road drainage and the water environment

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Table 9: Summary of proposed works to culverts ( Contractors Proposal for Drainage, 2009) From Table 9 above it can be seen that 6 of the 7 culverts will require modifications. Culvert C/5 will be replaced with a smaller (existing = 1200mm diameter, proposed = 900mm diameter) culvert since this will be conveying land drainage only and not highway runoff as was the case for the existing configuration. The design team plan to perform a survey on the drainage system. It is recommended that this includes a visual assessment of the culverts described above to identify any issues and mitigate against them. The complete drainage proposal therefore provides an acceptable mitigation against increasing flood risk. 5.5 Mitigation of Flood Risks from Infrastructure Failure The level of risk as a result of infrastructure failure is considered to be low. However, it is suggested that more details of the assets shown on the Severn Trent service layouts are obtained. Further ground investigation/trial pits may be required to identify the nature and location of Severn Trent’s assets which conflict with the location of the proposed scheme. Diversion of Severn Trent’s assets may be required. 5.6 Incidental Mitigation Measures Due to environmental concerns the river banks of the Avon will be widened to create habitat for otters. The extents of the widening has is not confirmed at this stage of the project. The effect of the river widening, though not the purpose, will be to increase the conveyance and storage capacity of the river channel, in turn lowering flood levels and flood risk. 24
5.7 Summary of Recommended Mitigation Measures Table 10 contains a summary of the recommended mitigation measures for the Carleton developments. Flood Risk Scheme may increase fluvial flood risk in downstream watercourses Scheme may be at risk of groundwater flooding Flooding to the site as result of failure of Artificial Drainage Systems Infrastructure Failure Recommended Mitigation • Reduce the runoff rates to 60% of existing values by introduction of attenuation ponds • Introduce flood plain compensation for locations where proposed development is within Flood Zone 3a • Consider signage at bridleway crossings to inform users of the risk of flooding • Introduce filter drains and slope face drainage where necessary to control groundwater levels • Perform more detailed drainage survey to identify existing issues with the drainage system and culverts • Regular maintenance of drainage system and culverts • Pursue Severn Trent for more details of their assets in the area, including Stamford reservoir upstream of scheme and potential water supply pipes which run through the site Table 10: Summary of recommended mitigation measures. 25
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M1 Junction 19 Improvement Environm
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M1 JUNCTION 19 IMPROVEMENT ENVIRONM
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Page 69 and 70: M1 JUNCTION 19 IMPROVEMENT ENVIRONM
Page 71 and 72: Appendix A - Pollution and Spillage
Page 73: Method D - Assessment of Pollution
Page 78 and 79: Groundwater: Hydrocarbons Hydrogeol
Page 83 and 84: Non Technical Summary Skanska Const
Page 85 and 86: Contents 1 Introduction 1 1.1 Overv
Page 87 and 88: 1 Introduction 1.1 Overview Jacobs
Page 89 and 90: 2 Policy Review 2.1 Planning Contex
Page 91 and 92: When the both the ‘Flood Zone’
Page 93 and 94: 3 Flood Risk to the Proposed Develo
Page 95 and 96: 3.2 Fluvial Flooding - Ordinary Wat
Page 97 and 98: Major earthworks affecting surface
Page 99 and 100: 3.7 Flooding from Infrastructure Fa
Page 101 and 102: 3.9 Summary of Risks to Site Table
Page 103 and 104: 4 Impacts of the Proposed Developme
Page 105 and 106: 4.6 Summary of Flood Impacts from D
Page 107 and 108: 5 Proposed Mitigation Measures 5.1
Page 109: The extents of this problem are cur
Page 113 and 114: 6 Residual Risks The level of flood
Page 115 and 116: 7 PPS25 Sequential and Exception Te
Page 117 and 118: 8 Conclusion The M1 Junction 19 Imp
Page 119 and 120: Appendix A Existing Layout, Environ
Page 127 and 128: Appendix B Contractor’s Proposals
Page 129 and 130: Appendix C Hydrogeological Assessme
Page 131 and 132: Memorandum Fairbairn House, Ashton
Page 133 and 134: Memorandum (Continued) Page 3 of 6
Page 135 and 136: Memorandum (Continued) Page 5 of 6
Page 141 and 142: Appendix D Volume Distribution for
Page 143 and 144: Floodplain compensation area - elev
Page 145: Depth Bands (m) TOTAL (m³) Area Re
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Chapter 9: Road drainage and the water environment

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