Strategic evaluation of flooding in mid Wales. Keywords Flooding & Risk Assessment Flood Alleviation Condition Survey Client, Architect & Other Organisations Powys County Council The Welsh Assembly Government

Background In Easter 1998 and again in October 2000 the market town of Welshpool was stranded by rising water following several days of heavy rainfall over the Welsh mountains.  The A483 trunk road crossing the flood plain of the River Severn to the north and south of the town making roads impassable to cars, heavy goods and emergency vehicles.   Routes to the east were severely compromised and local distributor roads became congested with traffic attempting to avoid or bypass the flooding.  The run-way at Mid-Wales airport was covered by approximately 3m of water which also caused significant damage to hangers and airport buildings.  The centre of Welshpool was spared the worst effects of the flooding although the Ledan and Ceunant Brooks did burst their banks flooding several residential properties and shops. Downstream on the River Severn there was significant flood damage to the English towns of Shrewsbury and Bewdley and the estimated cost of flood damage in the UK during the Easter floods of 1998 came to many billions of pounds.

Scope of Work Edenvale Young Associates in conjunction with Powys County Council has been working to evaluate strategic problems of flooding at Moor Straight on the A470 at Welshpool. In order to mitigate the effects of flooding the proposals made by Powys County Council were based upon raising the road in order to elevate the carriageway to a level where it would be less affected by flooding. The objective the work was to consider the implications of raising the road on the wider catchment and review the potential problems relating to obtaining the necessary approvals and consents. The project considered: The process of flooding, flood storage and flood storage compensation Legislation, approvals and consents Hydrology and on the preliminary analysis of extreme events Design and mitigation measures One of the most important aspects of the work was to assess the impact of climate change based upon the results of the UK Climate Impact Programme (UKCIP02).