Navigation Committee 21February 2014 Agenda Item No 13(i)

Broadland Flood Alleviation Project: Planning Application for Flood Defence Works in Compartment 17 – Postwick Marshes Report by Senior Waterways and Recreation Officer

Summary: This report provides members with a summary of Environmental Services Ltd (BESLs) planning application proposals for Compartment 17 (Postwick Marshes) on the true left bank of the between Postwick Grove and Ferry Lane Postwick immediately adjacent to the Broads Authority’s 24-hour mooring at Postwick Wharf. The report also outlines officers’ comment on the planning application upon which Members’ comments are welcomed.

1 Background

1.1 Compartment 17 is located on the true left bank of the River Yare between the Postwick Grove and Ferry Lane Postwick which is immediately adjacent to the Broads Authority’s 24-hour mooring at Postwick Wharf. Land in the compartment is protected by earth floodbank defences, concrete floodwalls and short lengths of steel sheet piling which provide erosion protection.

1.2 A planning application for flood defence works in Compartment 17 was submitted by the Environment agency in 2008 which proposed major flood defence works along the complete length of Compartment 17. This application was withdrawn as Natural was uncertain about how the proposed works might impact on the undefended Yare Broads and Marshes SSSI which is situated upstream of Rockland Dyke. NE required the Broadland Flood Alleviation Project to carry out study work to assess how flood defence works would affect water levels and flooding patterns in the Yare Valley.

1.3 Since 2008 a number of emergency repair schemes have been carried out in the compartment to protect vulnerable banks. This work, which included the installation of plastic crest piling in the centre of the compartment to reduce the risk of catastrophic floodbank breach, did not provide a long term sustainable solution for the defence of Postwick Marshes.

1.4 BESL has recently carried out further surveys of the flood defences in Compartment 17 and has concluded that there is a need to carry out further works in the Compartment.

2 BESL’s Planning Application for Compartment 19

3.1 BESL’s proposals for Compartment 17 involve 317m of floodbank strengthening, 515m of floodbank rollback, 55m of work raising a concrete

AC/RG/rpt/nc270214/p1of2/170214 wall and 440m of gabion basket installation. The location of these works is shown on the plans at Appendix 1.

3.2 The strengthening works amount to crest raising and widening of the existing bank and placement of material on its rear face. These works will have no impact on the navigation and will reduce the risk of the bank breaching during flood events.

3.3 Floodbank rollback will take place in the area of the previously installed crest piling and will involve the construction of a new bank on a slightly different alignment. These works accord with the standard flood defence solutions used by BESL elsewhere in the BFAP area and present officers with no concerns provided that appropriate conditions are placed on any planning permission granted requiring channel marking if necessary and erosion monitoring.

3.4 The installation of the proposed gabion basket does have the potential to impact on the navigation and while officers accept the proposed solution is appropriate it is suggested that a condition be placed on any planning permission granted for the scheme requiring appropriate channel marking to be installed to ensure that navigators are aware of the baskets. Additionally officers would recommend that a condition requiring the detail of the gabion design, including the height that they are set at and how they are filled should be placed on any planning permission granted.

4 Summary of Officers’ Comments

4.1 Officers are confident that the floodbank works proposed by BESL will have minimal impact on the navigation. Officers therefore propose to raise no objections to the works set out in the planning application but to recommend that BESL be required to agree the details of the proposed gabion baskets, any channel marking required and erosion monitoring by planning condition.

5 Conclusions

5.1 Members’ comments on the report and officers’ proposed response to the Consultation on the planning application are welcomed.

Background papers: Nil

Author: Adrian Clarke Date of report: 14 February 2014

Broads Plan Objectives: CC3.4

Appendices: APPENDIX 1 – Compartment 17 detailed maps.

AC/RG/rpt/nc270214/p2of2/170214 F PROPOSED STRENGTHEN BANK E R R Y

L PLANNING BOUNDARY A N E LIGHT VEHICLES ONLY

STRENGTHEN BANK CH0-73 REFER X-SECTION 1 1. NO DIMENSIONS TO BE SCALED FROM 0 THIS DRAWING. 2. ALL DIMENSIONS IN MILLIMETRES UNLESS NOTED OTHERWISE. STRENGTHEN BANK CH73-115 3. ALL LEVELS IN METRES ABOVE REFER X-SECTION 2 ORDNANCE DATUM.

4. EXISTING LEVELS TO BE MAINTAINED.

STRENGTHEN BANK CH115-220 REFER X-SECTION 3

E

R

A

Y

R

E

V I

R

0 0 2

FERRY HOUSE

Environment Agency

GD03177G

PLAN OF WORKS SCALE 1:1000

FOR Line of mature trees PLANNING 1.5m PURPOSES New strengthened floodbank to be created Wet woodland Approx. 1.4m (open to river) ONLY Varies Track Varies (Ferry Lane) 3 1

Existing dyke

Existing dual asbestos piling Broadland Environmental Services Limited A Joint Venture Company of Bam Nuttall Ltd and Halcrow Halcrow is a CH2M HILL company

3rd Floor Grosvenor House, 112-114 Prince of Wales Road, , NR1 1NS Tel 01603 226161 TYPICAL X-SECTION 1 Halcrow Group Limited STRENGTHEN BANK Ch0 - 73m Third Floor, Grosvenor House, 112-114 Prince of Wales Road, Norwich, . NR1 1NS Tel. 44 (0)1603 226161 SCALE 1:100 [email protected] www.halcrow.com

A CH2M HILL COMPANY

Line of mature trees BROADLAND FLOOD ALLEVIATION PROJECT Line of mature trees

COMPARTMENT 17 1.5m 1.5m Distance unknown (Approx. <10m) RIVER YARE New strengthened POSTWICK MARSHES Wet woodland Existing steel sheet piling, floodbank to be created Track Approx. 1.4m DETAILED PLAN AND SECTIONS (open to river) approx. 1m height visible (Ferry Lane) 2 Approx. 1.4m 3 Grip to be dug to link Track 1 SHEET 1 OF 3 3 1 internal drains (Ferry Lane) 1 Existing dyke Fill existing dyke where present Geotextile layer to be installed Existing dyke (unseen during walkover)

TYPICAL X-SECTION 2 TYPICAL X-SECTION 3 STRENGTHEN BANK Ch73 - 115m STRENGTHEN BANK Ch115 - 220m SCALE 1:100 SCALE 1:100 PROPOSED BANK STRENGTHENING

PROPOSED NEW SOKE DYKE

FLOODWALL RAISING

PLANNING APPLICATION BOUNDARY

ACCESS TRACK

1. NO DIMENSIONS TO BE SCALED FROM THIS DRAWING.

Existing track approx. 3m max. 2. ALL DIMENSIONS IN MILLIMETRES Proposed New Soke Dyke Rond 2m Folding 7m min. 6m max. UNLESS NOTED OTHERWISE.

Bank strengthening Ground to be 3. ALL LEVELS IN METRES ABOVE 2 1.4m reshaped behind track MHWS = 0.85m 1 3 ORDNANCE DATUM. 1 MLWS = 0.17m

River Yare

Approx. 2m 1 1 1 1 Ch1 100 Existing soke dyke backfilled using material excavated from new dyke New soke dyke to be excavated

TYPICAL X-SECTION 1 STRENGTHEN BANK Ch1103 - 1147m SCALE 1:100

Bank strengthening Ch1103-1147m Refer X-Section 1

Existing track approx. 3m max. Folding 7m min. Proposed New Soke Dyke 6m max.

1.4m MHWS = 0.85m Existing concrete floodwall to be raised, by approx. 350mm in places MLWS = 0.17m

River Yare Bank strengthening Ch1202-1224m Existing concrete floodwall FOR Refer X-Section 3 on 2.7m long piles Approx. 2m 1 1 1 00 1 12 Existing soke dyke (where located) backfilled PLANNING Ch using material excavated from new dyke PURPOSES Floodwall raising TYPICAL X-SECTION 2 Ch1147-1208m FLOOWALL RAISING Ch1147 - 1208m Refer X-Section 2 SCALE 1:100 ONLY

Existing soke dyke to be widened by 1.5m max. on marsh side along 40m max. length Broadland Environmental Services Limited A Joint Venture Company of 2m 1.5m Bam Nuttall Ltd and Halcrow Halcrow is a CH2M HILL company Bank strengthening using material 3rd Floor Grosvenor House, 112-114 Prince of Wales Road, Norwich, NR1 1NS from widened soke dyke Tel 01603 226161 2 Soke dyke to be widened by Halcrow Group Limited 1 3 1.5m on marsh side of existing Third Floor, Grosvenor House, 112-114 Prince of Wales Road, Norwich, Norfolk. NR1 1NS 1 Tel. 44 (0)1603 226161 [email protected] www.halcrow.com 1m 1 1 A CH2M HILL COMPANY

BROADLAND FLOOD ALLEVIATION PROJECT

COMPARTMENT 17 TYPICAL X-SECTION 2 RIVER YARE FLOOWALL RAISING Ch1147 - 1208m SCALE 1:100 POSTWICK MARSHES Ch1300 DETAILED PLAN AND SECTIONS SHEET 2 OF 3

Environment Agency

GD03177G PLAN OF WORKS SCALE 1:500 2 PROPOSED ROLLED BACK BANK 0 PROPOSED STRENGTHEN BANK 0 PROPOSED NEW SOKE DYKE 0 PLANNING APPLICATION BOUNDARY

1. NO DIMENSIONS TO BE SCALED FROM THIS DRAWING.

2 2. ALL DIMENSIONS IN MILLIMETRES 2 UNLESS NOTED OTHERWISE. 0 3. ALL LEVELS IN METRES ABOVE 0 ORDNANCE DATUM.

Rollbank bank Ch2085-2600m 2 Refer X-Section 1

4 2600 0 0

Environment Agency

GD03177G PLAN OF WORKS FOR SCALE 1:1000 PLANNING PURPOSES ONLY

Existing wooded rond 2.5m Folding 9m min. Proposed New Soke Dyke 18m max.

Vegetation from existing dyke Proposed rollback floodbank placed as berm in new dyke Existing bank to be regraded Broadland Environmental Services Limited to MHWS level 1.4m A Joint Venture Company of 2-3 Bam Nuttall Ltd and Halcrow MHWS = 0.85m Halcrow is a CH2M HILL company 1 3 3rd Floor Grosvenor House, 112-114 Prince of Wales Road, Norwich, NR1 1NS MLWS = 0.17m 1 Tel 01603 226161

River Yare Existing crest piling to be retained Halcrow Group Limited 1 Third Floor, Grosvenor House, 112-114 Prince of Wales Road, Norwich, Norfolk. NR1 1NS Approx. 2m Tel. 44 (0)1603 226161 1 1 [email protected] Max. 2m 1 www.halcrow.com

A CH2M HILL COMPANY Existing soke dyke to be backfilled New soke dyke to be excavated

TYPICAL X-SECTION 1 BROADLAND FLOOD ALLEVIATION PROJECT ROLLBACK BANK Ch2085 - 2600m SCALE 1:100 COMPARTMENT 17 RIVER YARE POSTWICK MARSHES DETAILED PLAN AND SECTIONS SHEET 3 OF 3 PLANNING APPLICATION BOUNDARY PROPOSED GABION BASKET INSTALLATION CH1357-1379m PROPOSED GABION BASKET E.P. REFER TYPICAL X-SECTION INSTALLATION 1400

1. NO DIMENSIONS TO BE SCALED FROM THIS DRAWING.

2. ALL DIMENSIONS IN MILLIMETRES UNLESS NOTED OTHERWISE.

3. ALL LEVELS IN METRES ABOVE ORDNANCE DATUM.

PROPOSED GABION BASKET INSTALLATION 1 CH1461-1747m 6 REFER TYPICAL X-SECTION 00

1 8 0 0 PROPOSED GABION BASKET INSTALLATION CH1778-1900m REFER TYPICAL X-SECTION

PROPOSED GABION BASKET INSTALLATION CH1929-1975m 2 REFER TYPICAL X-SECTION 0 0 0

Environment Agency

GD03177G PLAN OF WORKS FOR SCALE 1:2000 PLANNING

Existing floodbank PURPOSES Varies

MHWS = 0.85m ONLY

River Yare

Broadland Environmental Services Limited A Joint Venture Company of Bam Nuttall Ltd and Halcrow Halcrow is a CH2M HILL company

3rd Floor Grosvenor House, 112-114 Prince of Wales Road, Norwich, NR1 1NS Tel 01603 226161

CH2M Hill Existing Soke Dyke Third Floor, Grosvenor House, 112-114 Prince of Wales Road, Norwich, Norfolk. NR1 1NS Tel. 44 (0)1603 226161 [email protected] TYPICAL EXISTING RIVER SECTION www.halcrow.com SCALE 1:50 A CH2M HILL COMPANY Existing floodbank

BROADLAND FLOOD ALLEVIATION PROJECT MHWS = 0.85m

River Yare COMPARTMENT 17 RIVER YARE PROPOSED GABION BASKET Proposed gabions to be EROSION PROTECTION WORKS installed on front face of bank

Existing Soke Dyke

TYPICAL PROPOSED RIVER SECTION SCALE 1:50