The shorter lengths. Therefore, the measure is recommended

The economic viabilities of the three proposed measures, flood walls, weirs and demolition of structures in floodplain, for an area in Kilmarnock near River Irvine are discussed.The costs for a flood wall depend on the wall type, wall length and wall height. The costs vary with different types of walls. The critical factor for the costs of a flood wall is its length, calculated per metre, which is significantly higher for shorter lengths. Therefore, the measure is recommended at the area when longer flood wall lengths are required. The plan length of flood wall is 180 metres in average, according to the Unit Cost Database. Four height bands are provided with their corresponding costs in the Unit Cost Database, which are £1419 for less than 1.2 metres, £2905 for 1.2 to 2.1 metres, £3577 for 2.1 to 5.3 metres and £11168 for more than 5.3 metres, per metre for all wall types.The costs for weirs include direct construction costs, contractors’ overheads, temporary works and all associated works. According to the Unit Cost Database, the average costs per metre for four different types of weir, narrow fixed weir (<5 m), fixed weir (width 5-20 m), fixed weir (width 20-40 m) and movable weir are £29100, £6900, £2800 and £61100, respectively. The expected operation and maintenance costs for weirs are insignificant. Annual operation and maintenance works are negligible and specific risks increasing the expenditure of operation are minimised in most designs. Therefore, only the major costs are considered for River Irvine.Demolition costs are different for different land uses. There are four categories of site uses, including residential, employment, retail and industrial, each of them is sub categorised into non complex and complex. The costs include removal of redundant services, site investigation and fees, which are fixed per site, and site clearance and demolitions, which depends on the area of the site. According to Guidance on dereliction, demolition and remediation costs, the formers account for £120 to £1090 for each site and the laters account for £5 to £75 per square metre and £11 to £170 per square metre GEA.