Pdp Green Consulting were commissioned by the South West of England Regional Development Agency to undertake a Flood Risk Assessment (FRA) and Sustainable Drainage Scheme (SuDS) for an 11 Hectare commercial development site at Tolvaddon near Camborne in Cornwall. Whilst only a small proportion of the site was identified as being within Flood Zones 2 and 3 (medium and high risk), the size of the development required an assessment of the surface water generated by the development to be assessed and mitigation measures proposed to limit the surface water run-off to greenfield rates.
PDPG undertook a detailed study of the site to establish existing greenfield runoff rates and then compared these with calculated runoff rates for the proposed development. The study included calculation of pre and post development runoff volumes, impact on lag times and estimation of runoff hydrographs.
A drainage strategy was developed with close liaison with the Camborne, Pool, Redruth (CPR) Drainage Steering Group, The Red River Working Party, the Environment Agency and in accordance with the Integrated Urban Drainage (IUD) Strategy for the CPR area. The IUD strategy recommended that a policy of no infiltration was promoted, due to the high levels of naturally occurring contamination in the ground and the potential for ground water pollution, which is exacerbated by extensive mining in the area.
Based on the recommendations of the IUD strategy PDPG developed a drainage strategy for the whole site utilising strategically placed attenuation ponds with controlled outlets that maintain a discharge to the nearby water course equivalent to the green field runoff for the site.