River Engineering & Restoration
Welshpool Flooding Project Appraisal Study
Keywords: Flooding Project Appraisal River Modelling (FEH, ISIS-TUFLOW) Civil Engineering Design & Costing Asset Condition Assessment Strategic Flood Risk Mapping,
Flooding in Welshpool 1968
Client, Architect & Other Organisations
Powys County Council
Welsh Assembly Government
Description
In 1932, 1968 and 2000 there was significant flooding to large areas of the town from the Lledan Brook and this resulted in Powys County Council seeking grant aid funding from the Welsh Assembly Government. Edenvale Young Associates completed the pre-feasibility study for the site in 2002 which recommended that a full project appraisal study (PAS) should be undertaken.
The scope of works for the project appraisal a careful programme of work which included the procurement of LiDAR & topographic data; diving condition survey; hydrological modelling; interviews with flood affected residents; development of engineering designs; cost benefit analysis and environmental appraisal. In order to assess the extent of flooding in the urban area an ISIS-Tuflow was constructed to analyse flood damages within the town for a range of return periods.
The model included the Ceunant Brook, Bron-y-Buckley Brook and the LLedan Brook and spills to the Montgomery Canal in the centre of Welshpool. Particular technical problems which had to be addressed included the spills to the Montgomery Canal and surface connection between the TUFLOW domain and the 1.1km of culvert (Lledan Brook) running through Welshpool and modelled in 1D. Under a collaborative arrangement between PCC and the EA the scope of works was extended to include the production of flood mapping for the Environment Agency to update the flood mapping. The Welshpool ISIS-TUFLOW model has also been used to: prepare the Unitary Development Plan for Powys County Council; prepare a developer led FCA for the Smithfield site in Welshpool and derive flood forecasting data for a new gauge installed on the Lledan Brook.