Assessment against the Accounting Officer tests Regularity This assessment accompanied the OBC was approved by HM Treasury in June 2021. The project will be delivered in partnership by the Environment Agency ( EA) and Surrey County Council.
#Stone flood channels in altadena full
The OBC seeks approval to a cumulative Full Business Case ( FBC) development cost of £104 million which includes the advanced delivery of compensation habitat. The design and construction of the scheme will be procured via Public Contract Regulations 2015 using the Competitive Procedure with Negotiation. The scheme will reduce flood risk to 11,000 properties and infrastructure and avoid £2.7 billion of PV damage over 100 years.Ĭonstruction of the new flood channels will involve the excavation and reuse or disposal of 700,000mᶾ of material including landfill waste. The PV cost is now £346 million including a 48% contingency and the BCR is 7.97.
The Outline Business Case ( OBC) confirms a 2-channel variation of the option choice. The economic optimum option identified in the strategic outline case comprised 3 flood alleviation channels alongside the River Thames and improvements to 3 weirs at a present value ( PV) cost of £461 million and a benefit-cost ratio ( BCR) of 5. Junction 13 of the M25 is at risk of closure for several days and over 300 kilometres of other roads are at risk of flooding. More than 15,000 properties are at risk from a 1% annual exceedance probability ( AEP) flood and 10,000 from a 2% AEP flood, placing communities in Datchet, Wraysbury, Staines, Egham, Hythe, Chertsey, Laleham and Shepperton at risk. The Lower Thames floodplain is undefended between Datchet and Teddington.
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