Chapter 9: Road drainage and the water environment

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Mitigation measures to reduce the impact of groundwater flooding locally (on the scheme) are given in Section 0: Proposed Mitigation Measures. 4.3 Impacts on Flood Risk from Surface Water Runoff The scheme involves some major earthworks particularly in the construction of the M6-A14 link and the M1–A14 link, this is shown in Figure 3. The impact of the proposal will be to reduce the total area contributing to surface water runoff which would ordinarily have found its way into land drains and subsequently into the River Avon. The existing proposal of cuttings, embankments and highways will divert this surface water runoff into the proposed drainage system. Therefore the scheme will have an effect of reducing the surface water runoff and the associated risk. However, it is noted that this surface water will be managed differently in the current proposal i.e. transferred to the artificial drainage system, this is considered in the following section. 4.4 Impacts on Flooding from Artificial Drainage Systems The volume of runoff picked up by the artificial drainage system is set to increase following the proposed scheme because it will: • collect groundwater for the substantial cuttings • collect surface water which would have ordinarily infiltrated or have been intercepted by land drains • collect from a larger impermeable area The runoff from the existing drainage system discharges into nearby water courses which subsequently flow into the River Avon. The impact of the increased volume of runoff from various sources conveyed by the artificial drainage system may increase peak flow and thus flood risk in the River Avon. Arguably the time of concentrations from a catchment wide event would be very different between the natural catchment and the impermeable catchment. Despite this, mitigation measures should be considered (see Section 5). 4.5 Impacts on Flooding from Infrastructure Failure Construction of the scheme (particularly around the Swinford Road cutting and A14-M1 link) may damage the water supply pipelines through the site. Damage to these pipes could cause overland flows towards the site. Whilst, this flooding is not likely to cause a risk to highway users or the scheme in general, it could cause short term nuisance. Mitigation will be required on site to avoid any damage to these pipes. 18
4.6 Summary of Flood Impacts from Development Table 7 contains a summary of the potential impacts of the development on flood risk elsewhere. Proposed mitigation measures are discussed in Section 5. Flood Risk Impact on Risk Actions Required 6 Fluvial - Main River Fluvial – Ordinary Watercourse Medium Low Mitigation measures Mitigation measures Sea/Tidal None identified None Groundwater Low Mitigation measures Surface Water Runoff Artificial Drainage Systems Infrastructure Failure Low Low Low Mitigation measures Mitigation measures Mitigation measures Table 7: Potential impacts of the development on Flood Risk. 6 See Section 5 19
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M1 Junction 19 Improvement Environm
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M1 JUNCTION 19 IMPROVEMENT ENVIRONM
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Page 54 and 55: 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: 4 Impacts of the Proposed Developme
Page 107 and 108: 5 Proposed Mitigation Measures 5.1
Page 109 and 110: The extents of this problem are cur
Page 111 and 112: 5.7 Summary of Recommended Mitigati
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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