RIVER AVON TIDAL FLOOD RISK MANAGEMENT STRATEGY Short List Options Report July 2016 Prepared for Bristol City Council Issue Date Details Prepared by Checked by Approved by 1 26/05/16 Draft for client review Ben Taylor Jason David Dales Drummond Assistant Coastal Director Engineer Principal Flood and Coastal Jonathan Short Specialist Principal Consultant 2 08/07/16 Updated following client Ben Taylor Jason David Dales comments and comments Drummond Assistant Coastal Director from internal and external Engineer Principal Flood shortlisting workshops and Coastal Jonathan Short Specialist Principal Consultant 3 26/07/16 Final Jason Jonathan Short David Dales Drummond Principal Director Principal Flood Consultant and Coastal Specialist AECOM The Crescent Centre, Temple Back, Bristol, BS1 6EZ, United Kingdom SHORT LIST OPTIONS REPORT i Limitations AECOM Infrastructure & Environment UK Limited (“AECOM”) has prepared this Report for the sole use of Bristol City Council (“Client”) in accordance with the Agreement under which our services were performed River Avon Tidal Flood Risk Management Strategy RESP1007626 (23/10/15) and Response to Tender Submission Clarifications (03/11/15) (the “Agreement”). The report takes into account the particular instructions and requirements of the Client in accordance with the provisions of the Agreement. It is not intended for and cannot be relied upon by any third party. No liability is accepted by AECOM and no responsibility is undertaken to any third party. Information obtained by AECOM has not been independently verified by AECOM, unless otherwise stated in the Report. The methodology adopted and the sources of information used by AECOM in providing its services are outlined in this Report. The work described in this Report was undertaken between December 2015 and June 2016 and is based on the conditions encountered and the information available during the said period of time. The scope of this Report and the services are accordingly factually limited by these circumstances. Where assessments of works or costs identified in this Report are made, such assessments are based upon the information available at the time and where appropriate are subject to further investigations or information which may become available. Copyright © This Report is the copyright of AECOM Infrastructure & Environment UK Limited. Any unauthorised reproduction or usage by any person other than the addressee is strictly prohibited. SHORT LIST OPTIONS REPORT ii TABLE OF CONTENTS 1. EXECUTIVE SUMMARY ............................................................. 1 2. PROJECT BACKGROUND ......................................................... 4 2.1 Strategy objectives ...................................................................... 4 2.2 Previous studies and recommended options ............................... 4 2.3 Structure of this report ................................................................. 7 3. FLOOD RISK ............................................................................... 8 3.1 Overview of tidal flood risk in Bristol ............................................ 8 3.2 Extreme water levels adopted by the Strategy ............................. 8 3.3 What is at risk in Do Nothing? ...................................................... 9 3.4 What is at risk in Do Minimum? ................................................. 15 4. OPTION APPRAISAL OVERVIEW ............................................ 18 4.1 Purpose of this report ................................................................ 18 4.2 Option objectives ....................................................................... 18 4.3 Strategy time epochs ................................................................. 18 4.4 Potentially feasible measures .................................................... 18 4.5 Assessment of feasible measures ............................................. 21 5. DESCRIPTION OF MEASURES ............................................... 22 5.1 Do Minimum ............................................................................... 23 5.1.1 Description ................................................................................. 23 5.1.2 Technical Feasibility .................................................................. 24 5.1.3 Costs ......................................................................................... 24 5.1.4 Environmental impacts .............................................................. 24 5.1.5 Wider issues and opportunities .................................................. 25 5.2 Property Level Protection........................................................... 26 5.2.1 Description ................................................................................. 26 5.2.2 Technical Feasibility .................................................................. 26 5.2.3 Costs ......................................................................................... 27 5.2.4 Environmental impacts .............................................................. 31 5.2.5 Wider issues and opportunities .................................................. 31 5.3 High Defences ........................................................................... 32 5.3.1 Description ................................................................................. 32 5.3.2 Technical Feasibility .................................................................. 32 5.3.3 Costs ......................................................................................... 54 5.3.4 Environmental Impacts .............................................................. 58 5.3.5 Wider issues and opportunities .................................................. 59 5.4 Low Defences ............................................................................ 61 5.4.1 Description ................................................................................. 61 5.4.2 Technical feasibility .................................................................... 61 5.4.3 Costs ......................................................................................... 71 5.4.4 Environmental Impacts .............................................................. 78 5.4.5 Wider issues and opportunities .................................................. 79 5.5 Tidal Flood Barrier - Overview ................................................... 80 5.5.1 Background ................................................................................ 80 5.5.2 Research ................................................................................... 80 5.5.3 Barrier Design ............................................................................ 80 5.5.4 Location and Configuration ........................................................ 81 5.5.5 Wider Issues and Opportunities ................................................. 82 5.5.6 Barrier Options for Further Assessment..................................... 83 5.6 ‘Wide’ Tidal Barrier .................................................................... 85 5.6.1 Location ..................................................................................... 85 5.6.2 Description ................................................................................. 85 5.6.3 Technical Feasibility .................................................................. 87 5.6.4 Costs ......................................................................................... 87 5.6.5 Environmental Impacts .............................................................. 88 5.6.6 Wider Issues and Opportunities ................................................. 89 5.7 ‘Narrow’ Tidal Barrier ................................................................. 90 SHORT LIST OPTIONS REPORT iii 5.7.1 Location ..................................................................................... 90 5.7.2 Description - Ham Green / Nibley Road Barrier ......................... 90 5.7.3 Technical Feasibility - Ham Green / Nibley Road Barrier ........... 90 5.7.4 Description - Cumberland Basin Barrier .................................... 92 5.7.5 Technical Feasibility - Cumberland Basin Barrier ...................... 92 5.7.6 Costs ......................................................................................... 92 5.7.7 Environmental Impacts .............................................................. 93 5.7.8 Wider Issues and Opportunities ................................................. 94 6. OPTION APPRAISAL - LONG LIST TO SHORT LIST .............. 95 6.1 Methodology .............................................................................. 95 6.1.1 Multi-criteria appraisal ................................................................ 95 6.2 Description of long list options and scoring .............................. 100 6.3 Summary of Results ................................................................ 100 7. SELECTED SHORT LIST OPTIONS ....................................... 102 7.1 Overview of short list options ................................................... 102 7.2 Moderation and Rationalisation ............................................... 102 7.3 Discussion of the appraisal results .......................................... 106 7.3.1 Exclusion of Wide Barrier in the short list options .................... 106 7.3.2 Use of PLP and temporary / demountable defences and Do Minimum as a short term solution ............................................ 106 7.3.3 Impact of measures