Strategic Flood Risk Assessment - Wiltshire Council

Wiltshire CouncilSFRA High Level Executive Summary5.5 Raising Flood Defence Standards5.5.1 A design standard of 1 in 100 year annual probability is taken as the appropriate designstandard for fluvial defences. The majority of the flood defences within the study area currentlyhave a Standard of Protection (SoP) less than the 1 in 100 year annual probability. The SoPoffered by flood defences will be reduced further by the anticipated effects of climate changewith precautionary estimates indicating peak flows up to 20% greater than present.5.5.2 The costs of raising these defences to the 1 in 100 year design standard will vary considerably.The Salisbury Level 1 SFRA provides indicative costs for raising fluvial flood defences by alinear metre, these costs range from £500 to £3,000.5.5.3 Indicative capital costs for the provision of different types of flood defence have been providedbelow. Capital costs (CAPEX) for raising flood defences include the construction, preliminariesand site costs, enabling works and temporary works.5.5.4 The CAPEX used has been based on unit cost rates obtained from the Environment Agency 5 .The following tables provide indicative costs for the provision of new flood defence walls (Table5-1), new flood defence embankments (5.5.5 Table 5-2), upgrading of existing embankments (Table 5-3) and inclusion of outfall structures(Table 5-4).5.5.6 OPEX are the operational costs for a flood defence including maintenance and refurbishmentdepending on the proposed lifetime of the scheme. The following general assumptions havebeen made and can be applied to provide an indicative value for OPEX, these are:• Annual costs of maintenance of the flood defence are approximately 0.5% ofCAPEX; and• An allowance of 40% of the CAPEX should be made for refurbishment of the flooddefence every 25 years.Table 5-1: Indicative flood defence costs rates (per linear metre) – new walls (source:Environment Agency)Wall Height (m)Type of Wall