Entec and FRM > Project experience: Thames
Dartford Town Centre SFRA - ISIS-TuFLOW River Model Client: Dartford Borough Council The Dartford SFRA sits within the wider Kent Thameside SFRA (that Entec delivered) and provides specific guidance for the safe regeneration of Dartford Town Centre. The recommendations of the SFRA are based on the results of an ISIS-TuFLOW model of the River Darrent which Entec constructed. A significant flood risk was known to exist in Dartford, following the well-documented flood event of 1968. The River Darrent in Dartford is an interesting watercourse: over the years the channel has been elevated above the floodplain and moved to the valley side. This results in there being a disconnection between the river and its floodplain. This disconnection leads to the unusual situation of flood waters not being able to flow directly back into the channel once the flood peak has subsided. The ISIS-TuFLOW model enabled the extent of Flood Zone 3a to be redefined in the town centre and highlighted the areas where flood waters would pond following the passage of the flood peak. The 2-dimensional component of the model (TuFLOW) made it possible to predict flood hazard ratings and to identify flood flow routes. Key sites within the study area were assessed in detail providing issues for consideration in the masterplanning process. Information on the applicability of SuDS and guidance on how the sites could be safely developed (in line with the requirements of PPS25 and the Environment Agency) were incorporated in site specific discussions. |
Bexley SFRA - Tidal TuFLOW Breach Modelling - Surface Run-off Modelling
Client: London Borough of Bexley
Bexley is a London Borough Council, located on the southern bank of the Thames. Parts of the borough are within the Thames Gateway, one of the Government’s ‘Growth Areas’. This area has been identified as being integral to delivering housing targets.
Intense regeneration and development pressures required Bexley’s SFRA to include detailed modelling of the flood risk associated with a failure in the tidal flood defences along the banks of the Thames. A 2-dimensional model TuFLOW was used to simulate the breach scenarios.
TuFLOW enabled, flood depths, velocities, flow routes and flood hazards to be defined. These data were used to predict the extent of the residual risk zones to inform the spatial planning process. The Thames-side areas of Bexley are very low lying. If the defences were to fail, the TuFLOW modelling predicted that significant depths and high hazard values could develop. To provide differentiation within the hazard zones, the model was interrogated to divide up the flood extents on the basis of time to inundation.
The Pitt Review (2008) highlighted the impact of surface water flooding in the summer floods of 2007 and attributed this source of flooding for much of the damage caused. Due to the increased profile of this source of flooding and because Bexley has a well-documented history of surface-water related flood events, and this source of flooding was modelled. The FEH method was applied to derive effective rainfall volumes. These flows were then routed over the topography using the TuFLOW modelling software package. This generalised approach identified the potential major surface water flow routes and ponding areas. The SFRA included policy recommendations which advised surface water flooding to be considered for all development proposals within this zone.
Flood risk management guidance was prepared on three levels: management through the spatial planning process, management through the design process and management through emergency response.
Burnt Oak flood risk assessment
Client: Tesco Stores
Entec is carrying out an FRA for a site at Burnt Oak in NW London. The site is situated on the Silk Stream (a tributary of the River Brent) where the client proposes to build a retail store. The catchment is predominantly urban with suburban areas in the upper catchment. Underlying geology is clay. The catchment area is 29km2
To date the work has included a review of previous hydraulic modelling of the Silk Stream and its tributaries, to assess the effect of potential flood mitigation schemes. The model is a one dimensional ISIS model, originally built by the Environment Agency and since developed by other consultants. As part of this work Entec has carried out a review of the flood hydrology.
A second phase of work is currently underway to assess whether the 1D ISIS model is appropriate for modelling strategic storage schemes within the catchment. This includes a more comprehensive examination of the calibration data including refining the site hydrology.
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Flood resilience in London Client: Environment Agency Entec (in partnership with JBA) was appointed to undertake a study to assess the role in developing more sustainable flood management strategies within the Thames Estuary. This has focused on the Barking and Dagenham area of East London. Within this case study area, five issues relating to the role of ‘non-structural’ resilience measures in the future management of flood risk have been investigated. These were:
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East London Strategic Flood Risk Assessment Client: Thames Gateway London Partnership Entec was commissioned by Thames Gateway London Partnership (TGLP) to undertake a strategic flood risk assessment (SFRA) of East London. This study informs the future strategic planning of East London, ensuring that flood risk is considered in determining the type, location and design of development at a strategic scale. The assessment will also inform the preparation of the investment programme for Thames Gateway London. The Thames Gateway is one of four growth areas identified by the government in the Sustainable Communities Plan. The riparian brownfield sites of Thames Gateway London have been identified for redevelopment to provide at least 49,500 houses by 2016. The SFRA considered not only these sites, but also the area covered by the East London boroughs of Lewisham, Greenwich, Bexley, Havering, Barking and Dagenham, Newham, Waltham Forest, Redbridge, Hackney, Tower Hamlets and the Corporation of London. Entec, with JBA as sub-consultants, carried out the SFRA within the context of a drive to create sustainable numbers of new homes and jobs in East London over the next 20 years. The assessment has fully taken into account the radical changes in the statutory planning framework and the need to implement planning guidance specific to flood risk in East London. The assessment involved carrying out the sequential test recommended in PPG 25 to test proposed development and the existing development policies with respect to flood risk. The process included: reviewing existing data; producing graphical outputs showing sources of flood risk and existing flood defences and; applying the sequential test. Breach models were developed using TUFLOW and JFLOW 2D software to visualise residual flood risk in the event of defence failure and map the rapid inundation zones. Outline flood risk management options, which were costed for implementation within the Thames Gateway Development and Investment Framework, were proposed. |
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Crayford flood mitigation Client: London Borough of Bexley Entec was appointed by the London Borough of Bexley with funding from the Environment Agency to prepare a Strategic Flood Risk Assessment (SFRA) for Crayford Town Centre in compliance with guidelines set out in Planning Policy Statement 25: Development and Flood Risk (Dec 2006) (PPS25). A key feature of this study was to build a detailed hydrodynamic flood model of the town using the latest commercial 1D and 2D modelling techniques. This model was then used to assess current flood risk within the town as well as testing the feasibility and effectiveness of various flood risk mitigation options. The findings of the study were presented in an SFRA with an accompanying modelling report which included the findings from the options modelling. Options modelling looked at the impact on flood risk of increasing the storage volume of an upstream flood storage reservoir and opening up the culvert through part of the town centre. |
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