States of Jersey Transport and Technical Services Jersey DAP Needs Report July 2012 Prepared for: States of Jersey Transport and Technical Services Prepared by: Grontmij Grove House Mansion Gate Drive Leeds LS7 4DN T +44 (0)113 262 0000 F +44 (0)113 262 0737 E [email protected] Report Status: Rev 1 Job No: 692900 Name Signature Date Prepared By: Mandy Surradge Checked By: Ian Paterson Approved By: Mark Howard © Grontmij This document is a Grontmij confidential document; it may not be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, photocopying, recording or otherwise disclosed in whole or in part to any third party without our express prior written consent. It should be used by you and the permitted discloses for the purpose for which it has been submitted and for no other. States of Jersey Transport and Technical Services 1 Jersey DAP 692900 Needs Report States of Jersey Transport and Technical Services 1 INTRODUCTION ............................................................................................... 5 2 DESCRIPTION OF DRAINAGE AREA ............................................................. 6 3 SCOPE OF WORK ........................................................................................... 7 4 INFILTRATION STUDY .................................................................................... 9 4.1 INFILTRATION ASSESSMENT ........................................................................ 9 4.2 INFILTRATION LOCATIONS ............................................................................ 9 4.3 INFILTRATION ANNUAL PUMP COSTS ....................................................... 11 4.4 INFILTRATION SENSITIVITY ANALYSIS ...................................................... 11 5 MODEL UPDATES ......................................................................................... 13 5.1 BASELINE NEEDS MODEL ........................................................................... 13 5.2 BASELINE NEEDS MODEL WITH PHILIPS STREET SEWER SEPARATION SCHEME ................................................................................. 13 5.3 FUTURE NEEDS MODEL ............................................................................... 14 5.3.1 POPULATION ................................................................................................. 14 5.3.3 URBAN CREEP .............................................................................................. 16 6 BASELINE NEEDS ASSESSMENT (EXISTING SYSTEM) ............................ 17 6.1 HYDRAULIC / FLOODING PERFORMANCE ................................................. 17 6.2 KNOWN FLOODING LOCATIONS ................................................................. 17 6.3 TOWN CENTRE OF ST HELIER .................................................................... 17 6.4 ST AUBINS / CHARING CROSS AREA (SURFACE WATER FLOODING) ... 17 6.5 GUNSITE TOWER NEAR BEAUMONT SPS .................................................. 18 6.6 AREAS AT RISK OF FLOODING (FOUL / COMBINED SYSTEM) ................ 19 6.7 AREAS AT RISK OF FLOODING (SURFACE WATER SYSTEM) ................. 20 6.8 PUMPING STATION PERFORMANCE .......................................................... 20 6.9 OVERFLOW PERFORMANCE ....................................................................... 22 7 BASELINE NEEDS ASSESSMENT WITH PHILIPS STREET SCHEME ADDED ........................................................................................................... 26 7.1 OVERFLOW PERFORMANCE ....................................................................... 26 7.2 PERFORMANCE OF THE CAVERN .............................................................. 27 8 FUTURE NEEDS ASSESSMENT WITH CLIMATE CHANGE 2040 ............... 29 8.1 CLIMATE CHANGE PARAMETERS .............................................................. 29 8.2 HYDRAULIC / FLOODING PERFORMANCE ................................................. 29 8.3 KNOWN FLOODING LOCATIONS ................................................................. 30 8.3.1 TOWN CENTRE OF ST HELIER .................................................................... 30 8.3.2 GUNSITE TOWER NEAR BEAUMONT SPS .................................................. 30 States of Jersey Transport and Technical Services 2 Jersey DAP 692900 Needs Report States of Jersey Transport and Technical Services 8.4 AREAS AT RISK OF FLOODING (FOUL / COMBINED SYSTEM) ................ 30 8.5 AREAS AT RISK OF FLOODING (SURFACE WATER SYSTEM) ................. 30 8.6 OVERFLOW PERFORMANCE ....................................................................... 31 8.7 PERFORMANCE OF THE CAVERN .............................................................. 35 9 SPECIFIC STUDIES ....................................................................................... 36 9.1 BAUDRETTE BROOK ASSESSMENT ........................................................... 36 9.2 GLOUCESTER STREET SURFACE WATER SYSTEM ................................. 37 9.3 WEIGHBRIDGE SURFACE WATER SYSTEM ............................................... 38 9.4 THE CAVERN ASSESSMENT ........................................................................ 39 9.5 RISK OF SEDIMENTATION IN ST HELIER ................................................... 40 10 CONCLUSIONS .............................................................................................. 41 10.1 SPILLS TO SHELLFISH WATERS ................................................................. 41 10.2 OVERFLOWS IN JERSEY .............................................................................. 41 10.3 INFILTRATION STUDY .................................................................................. 41 10.4 FLOODING FOUL/COMBINED SYSTEM ....................................................... 41 10.5 FLOODING SURFACE WATER SYSTEM ...................................................... 41 10.6 PUMPING STATION PERFORMANCE .......................................................... 42 LIST OF TABLES Table 4.1 – Infiltration Between Mhs K08f049 To H08f017 ......................................... 9 Table 4.2 – Infiltration Between Mhs S11f055 And Pontac Sps ............................... 10 Table 4.3 – Infiltration Between Rue Des Buttes Sps And Mh H01f002 ................... 10 Table 4.4 – Infiltration Between Mhs 4156067699 And L08f162 ............................... 10 Table 4.4 – Infiltration Between Mhs 4156067699 And L08f162 ............................... 10 Table 4.4 – Infiltration Between Mhs 4156067699 And L08f162 ............................... 10 Table 4.5 – Infiltration Between Bas Du Marais Sps And Mh D04f007 ..................... 10 Table 4.5 – Infiltration Between Bas Du Marais Sps And Mh D04f007 ..................... 10 Table 4.6 Infiltration Sensitivity Analysis – Flood Volume Comparison ................. 11 Table 4.7 Infiltration Sensitivity Analysis – First Tower Sps Assessment .............. 12 Table 5.1 - Proposed Developments .......................................................................... 15 Table 5.1 - Proposed Developments .......................................................................... 15 Table 6.1 - St Aubins Sensitivity Analysis ................................................................. 18 Table 6.1 - St Aubins Sensitivity Analysis ................................................................. 18 Table 6.2 - Foul / Combined Predicted Flooding – St Aubins .................................. 18 Table 6.3 - Predicted Flooding – Beaumont Sps ....................................................... 19 States of Jersey Transport and Technical Services 3 Jersey DAP 692900 Needs Report States of Jersey Transport and Technical Services Table 6.4 - Overflow Performance Existing System ................................................. 23 Table 7.1 - Overflow Performance (10 Year Analysis) .............................................. 26 Table 7.2 - Overflow Performance (Annual Spill Analysis) ...................................... 27 Table 7.3 - The Cavern Assessment .......................................................................... 28 Table 8.1 - Foul / Combined Predicted Flooding Comparison – Beaumont Sps ..... 30 Table 8.2 - Overflow Performance (1 In 10 Year Spill Flow Comparison) ............... 31 Table 8.3 - Overflow Performance (Annual Spill Flow Comparison) ...................... 33 Table 9.1 - Baudrette Brook Predicted Flooding ....................................................... 36 Table 9.2 - Baudrette Brook Ps Flow (Existing System) ........................................... 37 Table 9.4 - Gloucester Street Sw System Predicted Flooding ................................. 37 Table 9.5 - Weighbridge Sw System Predicted Flooding ......................................... 38 Table 9.6 - West Of Albert Ps Flow (Existing System) .............................................. 39 Table 9.6 - West Of Albert Ps Flow (Existing System) .............................................. 39 Table 9.7 - West Of Albert Ps Flow (Climate Change) .............................................. 39 Table 9.8 - The Cavern Assessment .......................................................................... 40 States of Jersey Transport and Technical Services 4 Jersey DAP 692900 Needs Report States of Jersey Transport and Technical Services EXECUTIVE SUMMARY Grontmij were commissioned by States of Jersey (SoJ) to build and verify a hydraulic model of the Island of Jersey in The Channel Islands. The model was built in accordance