ED I NBVRGH. Biennial Flood Assessment Report. Transport, Infrastructure and Environment

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1 ED I NBVRGH THE CITY OF EDINBURGH COUNCIL 2Y Report Item no Biennial Flood Assessment Report Transport, Infrastructure and Environment 27 November 2007 Purpose of report 1 Publication of the City of Edinburgh Flood Assessment Report 2007, is a requirement of the Flood Prevention and Land Drainage (Scotland) Act This report is due for publication and is appended for the Committee s approval. Main report Under the Flood Prevention and Land Drainage (Scotland) Act 1997 local authorities are required to publish a report at 2 yearly intervals specifying: a b c the measures which they consider that they require to take to prevent or mitigate the flooding of land in their area. The measures which they have taken since the previous report to prevent or mitigate the flooding of land all occurrences of flooding since that date. In this context land means land other than agricultural land. The Council is the statutory Flood Prevention Authority. The previous report was published in November The 2007 report, now due for publication, meets the requirements of the Act. The report will be available for public viewing at: City Chambers, High Street Waverley Court Central Library, George IV Bridge Biennial Flood Assessment Report doc em 1

2 8 The report as appended does not contain photographs which will be included in the final publication. Financial Implications Revenue budget 9 The commitments made in this report can be met from the allocated Flood Prevention Revenue and Capital budgets. Capital Budget 10 Expenditure on the Water of Leith Flood Prevention Scheme and the Braid Burn Flood Prevention Scheme is the subject of separate Committee Reports. Recommendations 11 The Committee is asked to approve the publication of the report. Andrew Holmes Director of City Development Appendices Contacfltel Wards affected The City of Edinburgh Council Flood Assessment Report 2007 Mr Alvin Barber All Background Papers 2

3 THE CITY OF EDINBURGH COUNCIL THE CITY OF EDINBURGH COUNCIL FLOOD ASSESSMENT REPORT NOVEMBER 2007

4 PART 1 MEASURES WHICH TKE CITY OF EDINBURGH COUNCIL CONSIDER THAT TKEY REQUIRE TO TAKE TO PREVENT OR MITIGATE THE FLOODING OF LAND IN THEIR AREA. WATER OF LEITH CATCHMENT Water of Leith Flood Prevention Scheme The Water of Leith Flood Prevention Scheme was confirmed, with modifications, by the Scottish Ministers in March The modification ordered at Murrayfield is significantly different so as to require planning consent. It has also been found necessary to promote another flood scheme in the same area because the medium pressure gas main here is much closer to the proposed defences than was previously advised by Scotia Gas Networks. It is intended to invite tenders in the spring of 2008 from a shortlist of approved construction contractors with construction work programmed to commence in late The construction period for the scheme will be 3 years. The current estimated cost of the construction work is E35m. Progress of the flood prevention schemes continues to be reported to the Council at approximately 6 monthly intervals. In addition the Council's "Flood Protection" newsletters is distributed to over 7000 homes in flood risk areas to coincide with the progress reports. Port of Leith Current figures indicate that the lowest lying parts of Leith, principally around Bernard St, Salamander St. and Tower St, are on the limit of acceptable freeboard above the predicted 1:200 tidal flood level. Preliminary work is therefore to be undertaken on the assumption that sea level rise will make it advisable to construct flood defences in this area against extreme tide levels. Discussions will continue with Forth Ports PLC on issues regarding the proposed redevelopment of Leith Docks, which is now the subject of a planning application. BRAID BURNmIGGATE BURN CATCHMENT Carillion Regional Civil Engineering Ltd has been appointed to construct the Flood Defences. Work began on site in June 2007 and will continue for 3 years. Jordan Burn Further work is required to ascertain the condition of the culvert and identify areas where there may be blockage or restrictions. RIVER ALMOND CATCHMENT. Gogar Burn There is a large build up of sediment within the A720 Culvert downstream of Edinburgh Park as well in the burn downstream. It is intended to carry out sediment management of this section of the burn as well as removal of the Giant Hogweed and some bank stabilisation works with soft engineering (willow banking).

5 Niddrie Burn catchment A feasibility study is to be carried out to determine the most appropriate flood management actions. It is known that the housing at Ellen s Glen is at risk; the study will consider the whole watercourse including Little France, the New Royal Infirmary and Niddrie. The Council are currently considering a Planning Application for the Niddrie Burn River Restoration at Greendykes. This will form an open watercourse to the south of Greendykes and through the Jack Kane Centre, avoiding the culverted section under Niddrie. It will be carried out in conjunction with the new housing development, and will reduce flood risk to the Greendykes area which is under redevelopment. OTHER CATCHMENTS Willowbrae Road Ongoing works are planned to construct new manholes on the Dunsapie Loch overflow pipe to improve access for inspection. This will then allow for the CCTV survey and the next stage of pipe rehabilitation to take place. RESERVOIRS Repairs are required to penstock valves is in the interests of reservoir safety at Harperrig Reservoir. Painting of gantry bridges at Threipmuir and Harlaw, along with repairs to tower and valve gear, are necessary as priority maintenance. Repairs to access paths at Harlaw are necessary to provide safe access for staff and public. Further improvements are required to ensure full benefits are obtained from telemetry. Extreme Rainfall events and drainape The Strategic Flood Risk Assessment has shown the need for an assessment of the flood risk fiom extreme rainfall events which exceed the capacity of drainage systems. This will combine historical records (which are limited) with digital terrain modelling to identify the most vulnerable areas. Co-ordination will be required with Scottish water to identify appropriate actions. GENERAL Ongoing river maintenance work will be required based on the biannual inspection programme. Vulnerable culverts will require to be inspected monthly or more frequently in bad weather or during autumn. There are many culverted watercourses which are in unknown condition but have not caused any problems. In order to fulfil its duty to assess watercourses the Council has started a programme of internal CCTV inspections of these culverts. This programme will continue for several years and will identify any maintenance work required It is intended to enhance access provisions and improve inlet / screen arrangements at a number of culverts for maintenance purposes and to allow access for the surveys.

6 PART 2 MEASURES WHICH THE COUNCIL HAVE TAKEN SINCE THE DATE OF PUBLICATION OF THE PREVIOUS REPORT TO PREVENT OR MITIGATE THE FLOODING OF LAND Following each of the twice-yearly inspections, programmes were drawn up for the removal of' debris from all watercourses. This maintenance is ongoing throughout the year. Water Of Leith Catchment Water of Leith Flood Prevention Scheme. The additional sewer capacity required at Donaldson's College adjacent to Magdala Crescent is now complete and provides the much needed storage that allows the reduction in compensation flow in the Water of Leith. This reduction in compensation flow is a consequence of the permanent reservoir draw-down for the upstream flood water storage. This project was fully funded by the Council, but promoted by Scottish Water on behalf of the Council. Baird Drive A temporary demountable flood barrier has been installed at Pansy Walk, a weak point in the existing flood defences at Riversdale. Roseburn Cliff Bank erosion protection has been constructed in the form of willow banking. This will reduce the risk of channel blockage due to fallen trees or land slippage. Riversdale Crescent An additional 150meh-es of pallet barrier have been purchased for emergency use, including aluminium sheeting to cut down on storage space. Braid Burn Catchment Braid Burn Flood Prevention Scheme. Construction work has commenced on the Braid Burn Flood Prevention Scheme. The contractor has established his site compound at Inch Park and has begun the construction of flood storage reservoirs at Inch Park and the University of Edinburgh Playing Fields. The photographs below show the construction of a flood embankment adjacent to the Pow Burn (a tributary of the Braid Burn) in the University Playing Fields. The second photograph shows the diversion of a major gas main required prior to forming of floodwalls on Inch Park. The Construction of the flood defence embankment and associated drainage at Firrhill Campus by Volker Stevin Ltd is now complete.

7 It did not prove possible to advance work at Gilmerton Road due to difficulties in diverting a major sewer. However the replacement of the bridge at Oxgangs Road North is now complete. These works were undertaken by Carillion J M Ltd (formerly John Mowlem Ltd). The scheme cost was approximately E1.5million. The work comprised the construction of a new bridge, with associated roadworks and public utility diversions. Floodwalls between Oxgangs Road North and Firrhill Crescent were also constructed at this time to avoid future disruption in the area. The opportunity to incorporate an unsightly watermain on the structure of the new bridge was also taken. This involved close co-operation with Scottish Water. The Oxgangs Road North works will provide an immediate reduction in flood risk in this area, which will be improved further when the remainder of the scheme is built. Jordan Burn Culvert, Comiston The construction of 4 new manholes has been carried out in order to improve access and allow for the continuing CCTV survey of the existing culvert. Clearance of silt and debris was also undertaken from one of the new manholes at Maxwell Street. QUEENSFERRY Ferry Burn Culvert, South Queensferry The 120m long culvert at Jock s Hole was surveyed and found to be full of shopping trolleys. The trolleys and debris were removed and a new trash screen was installed. RIVER ALMOND CATCHMENT Bughtlin Burn The inlet to the existing culvert was improved and additional gullies installed to cope with run-off flooding. Ratho Station The culvert inlet has been cleared and a new trash screen installed to remove the risk of blockage within the culvert. Newbridge A secondary pipe was installed above an existing culvert at Murray International Metals in order to reduce flooding risk to properties upstream in the event of blockage. Kirkliston A new chamber and grille have been installed on the culvert at Manse Road to reduce blockage and ease clearing. Edinburgh Airport Proposals for improvements to the Gogar Bum have been brought forward through the Gogar Burn Partnership. Work is focussing at present on reducing the flood risk to the airport. Item 25 Biennial Flood Assessment Iceport Appendix

8 NIDDRIE BURN CATCHMENT Stenhouse Burn, Ellen s Glen Loan A CCTV survey of the existing culvert was carried out to establish the condition and debris accumulation. A bypass pipe has been constructed around the trash screen, this will allow the water to pass more easily when the screen becomes blocked allowing for easier clearance. Niddrie Burn, The Jewel Minor dredging work has been carried out at the mouth of the culvert and debris removed to reduce flooding. RESERVOIRS Transfer of Reservoirs The transfer of ownership of Harlaw, Threipmuir and Harperrig reservoirs from Scottish water to the Council took place on 1 March 2007, approximately 11 months after the initial target date, due to delay in completing the sale agreements. This will allow the council to control the reservoirs for flood prevention purposes and is compatible with the current flood prevention scheme. Since taking over the reservoirs an updated telemetry system has been installed giving improved internet access to reservoir levels as well as flow levels for the Water of Leith. Maintenance work at the reservoirs is necessary to meet the duties of a reservoir undertaker under the Reservoir Act Work that has been carried out includes: Bonaly Reservoir Repairs to outlet valve, draw-off tower and access road Threiprnuir & Harlaw Reservoirs Tree clearing and fencing work to improve safe public access. Replacement to automatic control apparatus and surveys of discharge pipes Harperrig Reservoirs Fencing work for control of livestock. Repair to damaged valve apparatus and assessment of other damage. COASTAL FLOODING Discussions have taken place, and are ongoing, with Forth Ports PLC to ensure that the redevelopments at Leith Docks and Granton do not increase the number of properties at risk of flooding.

9 GENERAL Strategic Flood Risk Assessment An assessment has been carried out to establish a procedure for filling the gaps in flood prevention strategy now that the Flood Prevention Schemes are under way. The highest priority actions, in particular the Niddrie Bum and to the risk of flooding from surface water and inadequate drainage, are described in this report. Tree Removal Several large fallen or damaged trees have been removed from various watercourses over the last 2 years. This includes the reiiioval of debris accumulation from weirs and bridge piers, mainly in the Water of Leith CCTV Surveys The CCTV surveys on culverted watercourses throughout Edinburgh are ongoing and these have already established blockages and possible future works. Emergency Planning The emergency Flood Action Packs have been updated to take account of the changes and improvements already carried out. Stockpiles of sandbags and proprietary flood barriers are inspected quarterly. Invasive species Clearance of invasive species vegetation has been undertaken prior to the flood prevention schemes being constructed. This is being incorporated into a wider programme of eradication in conjunction with other Council Departments.

10 PART 3 OCCURRENCES OF FLOODING OF LAND SINCE NOVEMBER 2005 The following are those occurrences of flooding known to the Council since the last report. They do not include agricultural land, or minor road flooding due to drainage problems unless buildings were affected. Sewer flooding is included where the Council are aware of it. Foul and surface water sewerage is the responsibility of Scottish Water. 2"d July 2006 Longstone Rd - Prison officer's club close to flooding. Sandbags deployed. Longstone Cres - gardens flooded. Cause - high levels in Murray Burn due to thunderstorm. Problem exacerbated by vegetation in channel. Spylaw St, Colinton - houses flooded. Cause - surface water and drainage surcharge; water floods houses due to local ground levels. Weaversknowe Cres -house close to flooding. Cause - sewer surcharging Lady Road - allotments flooded. Cause - Pow Burn flooding due to sewer overflow 20th June Oxgangs Rd North - garden flooded, house &L sub station close to flooding. Cause - thunderstorni. surface water, drains surcharging. Bellevue St - houses close to flooding. Cause - surface water and sewer surcharge Jeffrey St - hotel close to flooding. Cause - surface water from close. Lack of drainage East Market St - office slightly flooded. Cause - surface water from road Lady Road - allotments flooded. Pow Burn flooding due to sewer overflow Cameron Toll Centre. - Retail unit flooded. Cause - surcharged drains. St Catherine's Place - house close to flooding Cause - surface water from road Inverleith Row -house close to flooding. Cause - surcharging sewers/ drains Royal Cres - basement close to flooding. Cause - surface water from road Orchard Brae Gardens - house flooded. Cause - surcharged sewer Grassmarket - 4 shops flooded. Cause - surface water from road. ls'july Ellen's Glen Loan - house close to flooding. Sandbags deployed. Cause - grille choked. Mayfield Rd - 2 houses close to flooding. Cause - surcharge sewers Redford Ave - houses flooded. Cause - surcharged sewers John St -basement flooded. Cause - surface water from road. Broomfield Cres - houses close to flooding. Cause - surface water from road Fillyside Ave -house close to flooding. Cause - surface water from road The above events were short duration summer storms, and caused localised disruption and damage in many places. By their nature they are difficult to predict and to record. It is not often possible to state the exact cause, which is usually a combination of surface water and surcharged drainage. Local ground and floor levels dictate the seriousness of flooding. Following these events sandbags were issued to householders who requested them for use in the future. These records will be used for the purpose of the strategic flood risk assessment which is intended to determine those locations where action can reduce the flood risk.

11 This report was compiled by the Bridges and Flood Prevention Unit. If you have any queries other than translation please contact: Tom Dougall The City of Edinburgh Council Bridges and Flood Prevention Manager 1 Cockburn St Edinburgh EH1 1ZL Or telephone Alvin Barber on Item 25 Biennial Flood Asaessment Repoit Appendix