Chapter 9: Road drainage and the water environment

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M1 JUNCTION 19 IMPROVEMENT ENVIRONMENTAL STATEMENT VOLUME 2 CHAPTER 9 – ROAD DRAINAGE AND THE WATER ENVIRONMENT Page Not Used B0531000_ID_70-EIA Vol 2 Chap 9 Road Drainage and the Water Environment Final Rev 4.doc Page 46
M1 JUNCTION 19 IMPROVEMENT ENVIRONMENTAL STATEMENT VOLUME 2 CHAPTER 9 – ROAD DRAINAGE AND THE WATER ENVIRONMENT 9.9 SUMMARY 9.9.1 An assessment of the effects of the proposed junction improvement, in relation to surface water, groundwater and flood risk, has been undertaken following DMRB methodology, specifically developed for the assessment of the impacts of highway schemes, and based on advice from the EA. Impacts for the Catthorpe Viaduct have been indicated separately and included in combination with an overall assessment of the junction improvement. 9.9.2 Baseline conditions have been reviewed. The site is underlain by a mixture of non-aquifer and minor aquifers. The distribution of the latter are associated with the location of the various surface watercourses. The site lies within the catchment of the River Avon, a main river, and the highway crosses the River Avon at a number of locations. There is one other main river, the Clay Coton Yelvertoft Brook. There are numerous other ordinary watercourses / drainage ditches and ponds. 9.9.3 There are some groundwater abstractions, including private potable supply, located within 1km of the highway, presumed to be sourced from the minor aquifer. There are no surface water abstractions, although there is an important public water supply abstraction some seven kilometres downstream on the River Avon. 9.9.4 The main rivers are of good water quality. However, the existing highway drainage undergoes little treatment prior to discharge and, in addition, these receiving watercourses are very vulnerable to pollution incidents. 9.9.5 Without mitigation, construction work has the potential to adversely impact the water environment. The main potential impact is pollution of surface waters. It is assumed that good site practice as incorporated within and fundamental to the CEMP would be followed during the construction phase. The overall assessment score for the construction phase is of a Moderate Adverse effect – however, this is considered to be conservative as it reflects the inclusion of potential pollution of the River Avon drinking water supply. This would be a temporary risk, and of very short potential duration as the treatment ponds would be constructed early, providing mitigation for accidental spillage. 9.9.6 For the proposed junction improvement, the drainage scheme for the highway operation would upgrade the existing arrangements with spillage containment, water treatment and attenuation where required. It is assumed that maintenance and management of the operational scheme would be undertaken as necessary. The overall assessment score for the operational phase is of a Slight Beneficial effect. 9.9.7 With respect to groundwater, there is a potential for construction of cuttings to lead to a lowering of the water table within the minor aquifer. However, this effect would be localised and of Neutral significance. Other impacts on groundwater are relatively insignificant, and few mitigation measures are proposed or required. This results in the residual impact being little changed from the current situation. 9.9.8 In terms of flood risk, the widening of the A14 embankments and the creation of two bridleway bridges would reduce the storage capacity in the River Avon floodplain. However, flood compensation would be provided and so there would be no net loss of flood storage. Attenuation ponds would reduce the discharge rate for highway runoff across the scheme by at least 20%, and would therefore have a Slight Beneficial effect on flood risk. 9.9.9 The junction improvement would satisfy the requirements of DMRB for routine runoff and pollution incidents from accidental spillages. Details of the DMRB calculations are included in Appendix A. B0531000_ID_70-EIA Vol 2 Chap 9 Road Drainage and the Water Environment Final Rev 4.doc Page 47
Page 1: M1 Junction 19 Improvement Environm
Page 4 and 5: 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
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4 Impacts of the Proposed Developme
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4.6 Summary of Flood Impacts from D
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5 Proposed Mitigation Measures 5.1
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The extents of this problem are cur
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5.7 Summary of Recommended Mitigati
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6 Residual Risks The level of flood
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7 PPS25 Sequential and Exception Te
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8 Conclusion The M1 Junction 19 Imp
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Appendix A Existing Layout, Environ
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Appendix B Contractor’s Proposals
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Appendix C Hydrogeological Assessme
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Memorandum Fairbairn House, Ashton
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Memorandum (Continued) Page 3 of 6
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Memorandum (Continued) Page 5 of 6
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Appendix D Volume Distribution for
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Floodplain compensation area - elev
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Depth Bands (m) TOTAL (m³) Area Re
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Chapter 9: Road drainage and the water environment

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