Entec and FRM > Project experience: South West
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Flood Risk Assessment of Water Supply Assets Client: Bristol Water In common with most water companies, the need to locate water abstraction and treatment infrastructure close to water sources means that inevitably there will be a degree of flood risk to some assets, and Entec has been working with Bristol Water to assess these risks. The assessments have involved the investigation of flood risk from all sources of flooding (i.e. fluvial, tidal, groundwater and surface-water). On one site where existing flood levels were not available Entec constructed a hydraulic model of the local watercourse in HEC-RAS. For another existing Environment Agency flood level data for the estuary was compared with high-resolution elevation data (LIDAR) in order to derive flood extents and depths. The flood events with annual probabilities of 1%, 0.5% (tidal) and 0.1% were investigated, with additional scenarios including for climate change. Climate change (sea level rise and potential increases in rainfall intensity) have been considered following the guidance given in the latest Defra climate change update over the business plan period. The assessments have also considered the protection provided by existing flood defences, and have looked at the wider flood-resilience picture, including impacts on site accessibility and power supply. Recommendations have been made for further consultation and investigation where liaison is required with key stakeholders, alongside those for asset raising and protection. |
Integrated urban drainage pilot study
Client: Camborne-Pool-Redruth Urban Regeneration / Defra
The CPR Integrated Urban Drainage (IUD) Pilot Study is one of 15 pilot studies commissioned by Defra across England in 2007-8 to better understand the causes of urban flooding, test new approaches and examine the effectiveness of partnership working. The study was led by a steering group led by CPR Regeneration (URC) including representatives from the Environment Agency, Kerrier District Council, South West Water, Cornwall County Council, Red River Working Party and South West Regional Development Agency. Entec UK were the consultants to CPR and carried out most of the technical work, facilitated meetings and prepared the reports.
Camborne-Pool-Redruth (CPR) is a former mining area in south Cornwall with a substantial housing regeneration programme. It has a number of drainage problems including lack of sewerage capacity and poor water quality in receiving watercourses. The area is underlain by deep mines which contribute poor water quality base flow to the watercourses. The main deliverable was a Surface Water Management Plan (SWMP) providing overarching guidance on the development of strategic drainage infrastructure to meet development targets up to 2026. The study included the formulation of general drainage principles for the area, and the development of a strategic approach to modelling based on 8 sub-catchments established during the study. The main guiding principle established by the study was to reduce loading on the sewerage system by establishing above-ground strategic drainage systems incorporating overland routes and storage areas linked to green corridors and other amenity features.
The study included a report to Defra describing the approaches and methods used in developing the SWMP. The report also set out the main benefits of the SWMP which include allowing forward planning for new development infrastructure, providing firmer guidance for developers, facilitation of new development by releasing foul flow capacity and improvement in water quality. It will also allow the LPA to plan in advance to mitigate the flooding impacts of climate change. The report proposed the long-term adoption of the SWMP as a planning support document, to be held by the LPA as a ‘live’ document. A Drainage Trust is to be set up to operate and maintain the strategic drainage infrastructure. The form that this trust will take is the subject of further investigation. It is hoped that this pioneer study can provide a template for further IUD studies of this nature.
Redruth Corridor flood risk assessment
Client: Kerrier District Council
The Redruth Corridor FRA was commissioned by Kerrier District Council Major Projects Team, (MPT) to inform their masterplanning of the Redruth Town Centre regeneration. Redruth is one of the three towns that form the CPR Integrated Urban Drainage Study. The Redruth drainage systems are heavily modified, with the underlying geology having been mined for tin and the surface water systems altered for the use of tin streaming. The original watercourse has been entirely culverted through the town, with leats the remaining open surface water systems, which are perched on the valley sides.
Modelling of the leat systems was carried out to determine capacities, however, due to the interconnections between the leats and the culverted watercourse not being clearly understood and also the lack of data on the culverted watercourse, the full Flood Risk could not be determined. The findings of the project resulted in further recommendations for data collection and assessment.
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