Case Study De-culverting London This report was prepared by the NWRM project, led by Office International de l’Eau (OIEau), in consortium with Actéon Environment (France), AMEC Foster Wheeler (United Kingdom), BEF (Baltic States), ENVECO (Sweden), IACO (Cyprus/Greece), IMDEA Water (Spain), REC (Hungary/Central & Eastern Europe), REKK inc. (Hungary), SLU (Sweden) and SRUC (UK) under contract 07.0330/2013/659147/SER/ENV.C1 for the Directorate-General for Environment of the European Commission. The information and views set out in this report represent NWRM project’s views on the subject matter and do not necessarily reflect the official opinion of the Commission. The Commission does not guarantee the accuracy of the data included in this report. Neither the Commission nor any person acting on the Commission’s behalf may be held Key words: Biophysical impact, runoff, water retention, effectiveness - Please consult the NWRM glossary for more information. NWRM project publications are available at http://www.nwrm.eu Table of content I. Basic Information .................................................................................................................1 II. Policy context and design targets ..........................................................................................2 III. Site characteristics .................................................................................................................3 IV. Design & implementation parameters ...................................................................................3 V. Biophysical impacts...............................................................................................................5 VI. Socio-Economic Information ...............................................................................................6 VII. Monitoring & maintenance requirements ..............................................................................7 VIII. Performance metrics and assessment criteria ......................................................................8 IX. Main risks, implications, enabling factors and preconditions .................................................9 X. Lessons learned ...................................................................................................................10 XI. References ..........................................................................................................................10 XII. Photos Gallery ....................................................................................................................12 1 CS: De-culverting London, UK I. Basic Information Application ID United Kingdom_02 Application Name De-culverting_London Application Location Country: United Kingdom Country 2: NUTS2 Code (select from list in UKI1-Inner London Annex 1) River Basin District Code UK06-Thames WFD Water Body Code GB106039023290 Description The case study is located in south eastern part of the United Kingdom, in south east London. A heavily urbanised area, at an altitude of approximately 70m AOD. Application Site Coordinates Latitude: 51.455042 Longitude: 0.030134 (in ETRS89 or WGS84 the coordinate - ETRS89 or WGS84? Specify: - ETRS89 or WGS84? Specify: system) WGS84 WGS84 Target Sector(s) Primary: Urban Implemented NWRM(s) Measure #1: N4 Measure #2: N3 Measure #3: U11 Application short description The River Quaggy had a suite of NWRM features implemented as part of a flood alleviation scheme between 1990 and 2005. The main components included: - In the upper reaches this included returning to the surface a culverted underground section of the river and creating associated floodplain (Sutcliffe Park). - A detention basin was created at Weigall Road sports grounds for flood storage - Further downstream, set-back flood defences were constructed in private gardens adjacent to the river, and channel re-profiling undertaken. A map of the locations of measures along the River Quaggy can be seen in section 12. 2 CS: De-culverting London, UK II. Policy context and design targets Brief description of the problem As urban development in the River Quaggy river valley and natural to be tackled flood plain, near Lewisham in central London, is increasing, fluvial flooding experienced by local residents and businesses has increased. In 1968 the centre of Lewisham flooded to a depth in excess of 1m, and more recent flood events have occurred. A flood alleviation scheme was required to prevent further loss to the remaining floodplain within the catchment. What were the primary & Primary target #1: Flood control and flood risk mitigation secondary targets when designing Secondary target #1: Regulation of hydrological cycle and water this application? flow Which specific types of pressures Pressure #1: Other non EU- Natural Exceedence - did you aim at mitigating? Directive (specify) Flooding of land by waters exceeding the capacity of their carrying channel or the level of adjacent lands. Pressure #2: Other non EU- Physical alteration of Directive (specify) channel/bed/riparian area/shore of water body for flood protection Pressure #3: Other non EU- Diffuse - Urban runoff - Directive (specify) Storm overflows and discharges in urbanized areas not identified as point source Remarks The flood alleviation scheme was implemented between 1990 and 2005, prior to WFD and FD, but subsequent comparison shows compliance with and benefits to a number of the Directives. Which specific types of adverse Impact #1: Other non EU- Property- Adverse impacts did you aim at Directive (specify) consequences to property mitigating? and businesses. Remarks The flood alleviation scheme was implemented between 1990 and 2005, prior to WFD and FD, but subsequent comparison shows compliance with or support for those directives. Which EU requirements and EU Requirement #1: Floods Directive- Address risk of flooding Directives were aimed at being mitigating Flood Risk to local and downstream addressed? properties. Requirement #2: WFD-mitigation of De-culverting significant pressure Remarks As noted above, the WFD and FD were not in place at the time of implementation. Nevertheless the measures directly contribute to the FD and WFD objectives. Which national and/or regional The WFD and FD were not in place at the time of implementation, policy challenges and/or but comparison has subsequently been made with these and a 3 CS: De-culverting London, UK requirements aimed to be number of local policies for which the scheme is complaint. A addressed? number of these policies include: - London Green Infrastructure Policy - Thames catchment flood management Plan - London Green Infrastructure blue ribbon network Policy - London Borough of Lewisham River Policy. III. Site characteristics Dominant land use 111 - Continuous urban fabric Secondary land use 142 - Sport and leisure facilities Dominant Land Use type(s) Other important land use 141 – Green urban areas Remarks Climate zone cool temperate moist Soil type Gleysols/ Luvisols Average Slope gentle (2-5%) Mean Annual Rainfall 600 - 900 mm Mean Annual Runoff 150 - 300 mm 40 - 60% Average Runoff coefficient (or % imperviousness on site) Based on estimate of the Urban extent across the catchment. Characterization of water quality Although it is known that water quality monitoring was undertaken status (prior to the prior to the implementation of the measures, the report with this implementation of the information was not available. NWRMs) Positive way: The existing open spaces for recreation etc within the urbanized catchment were crucial to the effectiveness of the measures. The available green space at Sutcliffe Park ensured that Comment on any specific site bringing the culverted channel to the surface and creating characteristic that influences the operational flood plain worked effectively within the urban area. effectiveness of the applied The availability of gardens adjacent to the watercourse, downstream NWRM(s) in a positive or of Manor Park, allowed the effective implementation and operation negative way of the set back flood defences in a highly residential area. Negative way: None identified IV. Design & implementation parameters Medium (eg. public park, new Project scale Tributary catchment scale development district) Date of installation/construction Implementation between 1990 and (MM.YYYY) 2005 Lifespan of the individual Time frame Expected average lifespan (life NWRMs varies, but overall expectancy) of the application in expected to be 50+ years with years occasional maintenance. 4 CS: De-culverting London, UK Name of responsible authority/ Role, responsibilities stakeholder Implementation; co- 1.Environment Agency ordination; financial Co-ordination, implementation 2. Quaggy Waterways Action and continued support for the Responsible authority and other Group scheme stakeholders involved Provision of land; support for 3. Local Residents scheme Support for the scheme and 4. London Borough of Greenwich maintenance. Support for the scheme and 5. London Borough of Sutton maintenance. The application was initiated Environment Agency and Quaggy Waterways Action Group and financed by The primary principle was to ensure effectiveness in managing What were specific principles downstream flooding. As part of this aesthetic benefit was a key that were followed in the design requirement to ensure no loss of the green areas already limited of this application? within the urban environment. In order to enable this, it was also important to have landowner acceptability and involvement.