A 1D hydrodynamic model for the Upper Irvine catchment has been developed using Hec-RAS in order to ascertain the effectiveness of local flood risk management strategy (for Kilmarnock, Crookedholm, Hurlford and Galston) and determine how it has been influenced by the changing political climate of the last decade. Without defences serious flood inundation issues affect the urban areas along the Irvine valley; inundation depths of up to 2.55m and extents of up to 832m are modelled for a 1in200yr R.P. event, requiring substantial flood protection measures in response. Three main flood protection scenarios are analysed; the implemented 1in100yr R.P. 2001 scheme (downstream), the proposed 1in200yr R.P. 2005 scheme (upstream) and the combined 2001 & 2005 schemes. The combined scheme shows considerable improvement over the individual schemes; a 21.52% reduction in discharge, more than a 30% reduction in floodplain inundation depths and over 34% decrease in averageflood extent. However, water surface elevations suggest that individual flood protection schemes operate optimally for the R.P. they were designed for; whereas when combined there are local compromises in efficiency and reductions in performance.Detailed analysis of the combined scheme at the 1in200yr R.P. protection advocated by SPP7 illustrates a 12% under-design in the protection of Crookedholm, requiring £90k of retrofitting, and a 68% over-design at Kilmarnock that translates as a £2.8M overspend (CESSM, 1996). Indirect attenuation measures are more efficient than direct levees/floodwalls, yet under-design in all three schemes breaches current SPP7 legislation for the provision of compensation storage. A remedial £0.2M attenuation storage scheme on the Cessnock Water tributary is proposed. Results clearly illustrate that changes in policy, design R.P. and retrospective construction of the 2005 defenses upstream of the 2001 scheme have adversely effected the design and performance of the earlier 2001 scheme. This supports SPP7 in encouraging a more sustainable and catchment-wide focus on flood defence strategy within Scotland.
|Publication status||Published - 10 Oct 2007|
- flood management
- upper river Irvine
- hydrodynamic model
- flood protection