Roeshot Hill, Christchurch

PFA Consulting provided professional services to Taylor Wimpey UK Ltd to support the outline planning application for the Christchurch Urban Extension strategic housing allocation at Roeshot Hill.

A Flood Risk Assessment (FRA) and Hydrology, Drainage and Flood Risk Environmental Statement chapter was produced. The FRA assessed all sources of flood risk and identified conflicting sources of information for the flood hazard posed by the River Mude. The FRA was supported by a detailed flood modelling study of the River Mude to define flood risks on the site and propose flood risk management measures. The flood modelling study clarified the extents of the functional floodplain and the extents of the extreme floodplain (1 in 1000 year return period) for the River Mude. This enabled development areas to be set satisfying the requirements of the National Planning Policy Framework (NPPF), and its planning practice guidance. In addition floodplain compensation was designed and modelled to mitigate the effect of upgrading the watercourse crossing.

In addition, preliminary surface water and foul water drainage strategies were produced. The surface water drainage proposed swales to collect and convey runoff through the development site and drain into attenuation basins adjacent to the River Mude. Runoff is temporarily stored before released into the watercourse at greenfield runoff rates. The use of swales overcame issues with site levels and need to minimise ground raising while still achieving a gravity connection to the River Mude. A foul water drainage strategy for the site was devised in consultation with Wessex Water with a series of interconnected pumping stations which make a direct connection into the Sewage Treatment Works.