Least-Cost Path Analysis to Identify Retrofit Surface-Water Conveyance Solutions

Little guidance is available on how to identify optimally managed surface flood routes that can be engineered into the existing built environment. This paper addresses that gap. A least-cost path analysis was used to develop a tool based on topography and land use that automates and reduces the subjectivity in the search for viable surface-water conveyance solutions. The method is aimed at planning authorities who may use the tool to develop long-term strategic planning initiatives that identify key areas within the catchment where there is the opportunity to implement and manage flood flow routes. The least-cost path methodology was applied to identify the optimum retrofit-managed surface-water flood routes in Keighley, West Yorkshire, U.K. Three potential solutions were selected, and all three solutions reduced the number of flooded properties and enabled the surface-water catchments to retain greater proportions of the excess surface water within the catchment at non risk locations. The methodology provides the opportunity to identify the effect of each solution and hence to optimally manage the potential flood risk at an estimated cost. The least-cost path analysis to identify retrofit solutions has exciting potential for studies that need to build capacity and cope with climate change. However, the methodology has limitations in that it is highly dependent on the cost function that represents topography and land use. Costs associated with selected flood routes are extremely difficult to quantify, but such limitations will be overcome as additional cost and benefit data are made available from the implementation of a wider number of flood mitigation and rehabilitation measures. The least-cost path analysis offers a simple optioneering method that does not involve hydraulic analysis. Once a number of options have been identified, hydraulic analysis would be the next step in finding a viable solution.