River Engineering & Restoration
Knighton Flooding Project Appraisal Study
Keywords: Flooding and Flood Risk Assessment, Economic Environmental and Social Appraisal Condition Survey FEH & ISIS.
Client, Architect & Other Organisations
Powys County Council
The Welsh Assembly Government
Approximately 50 properties, are at risk of flooding from the River Teme and Wylcwm Brook in Knighton. The mechanism for flooding from the Teme is primarily associated with high flows in the river. However, there are a number of features in Knighton which could be exacerbating the effects of flooding. These include a reduction of the flood plain width at the Mill, encroachment on flood storage areas and the limiting cross section of the Teme Bridges.
Flooding in the town is also affected by the Wylcwm Brook which is a small ordinary watercourse which joins the Teme upstream of the Teme Bridge. During heavy rainfall the Brook overtops a bridge at Bowling Green Lane flooding three properties adjacent to the bridge. Overland flow also exacerbates flooding to commercial properties at Teme Bridge
Scope of Work
In 2002 Edenvale Young Associates completed a pre-feasibility study which recommended that a full project appraisal study should be undertaken to evaluate options to mitigate flooding in the town. Powys County Council asked Edenvale Young (then JYA Ltd) to prepare a full project appraisal. In summer 2004 a baseline ecological survey was completed and a topographic survey was commissioned to provide data for the hydraulic modelling. Following the completion of the field work, a hydrological analysis using FEH was undertaken to evaluate extreme flood flows.
In October 2004 ISIS model of the Teme and Wylcwm Brook was also developed and calibrated against the 2000 event using EA gauge data from Teme Bridge and information obtained from interviews with residents. This model has been used to evaluate a number of engineering options and to develop the economic assessment for the Project Appraisal Report.