Improved techno-economic evaluation of Blue Green Solutions for managing flood risk to infrastructure

The increased frequency of extreme weather events associated with climate change results in the increased risk of surface water (pluvial) flooding, posing a great threat to the integrity and function of critical urban infrastructure. During the winter of 2013/14 twelve major winter storms occurred resulting in more than 5,000 homes, businesses and infrastructure being flooded in southern England. Green infrastructure, in the form of Sustainable Urban Drainage Systems (SUDS), has been proposed as a potential measure that is likely to have a significant effect on flood risk in urban environments. However, despite their multifunctional benefits, SUDS often fail the feasibility criteria of Flood Risk Management (FRM) cost-benefit assessment. The Environment Agency (EA) highlighted a number of knowledge gaps concerning the cost and benefits of large-scale SUDS retrofitting schemes, in particular the data to remove uncertainties concerning the economic appraisal of innovative solutions.

The scientific community and engineering consultants have also recognised the importance of utilising vegetation to enhance urban water management by delivering a range of essential services to towns and cities and supporting urban adaptation to climate change. The Climate-KIC funded Blue Green Dream (BGD) project gathered eminent partners to develop tools for assessing the interactions between urban water (blue) systems and vegetated (green) areas and hence maximise the multifunctional benefits of so-called Blue Green Solutions (including SUDS). Building on that research, this project will assign green infrastructure interventions as assets by progressing knowledge and understanding of the ability of Blue Green Solutions to provide cost-beneficial Flood Risk Management services. This will be achieved by brining together the expertise from three BGD project partners - Imperial College London, Deltares and AECOM, supported by the EA Water London Team. The Decoy Brook sub-catchment in London Borough of Barnet will be used as a case study for: a) mapping of Blue Green Solutions for infrastructure protection using the Adaptation Support Tool; b) improving the cost-benefit assessment of SUDS by quantifying multifunctional benefits of innovative Blue Green Solutions; and c) producing an advanced tool for full cost-benefit analysis of the proposed SUDS retrofitting scheme in compliance with the Flood Risk Management assessment. This will enable the EA to transparently and objectively assess Blue Green Solutions against the broad range of benefits. In addition, it will provide AECOM an example of a robust business case for utilising SUDS/Blue Green Solutions to protect infrastructure that addresses the reduction in the levels of uncertainty associated with the results from such analyses. Outputs from this project will be used to provide evidence to the Greater London Authority on the development of a pan London approach to delivering sustainable drainage systems. In addition, more accurate and robust valuing of SUDS and demonstrating the full return on each pound invested will enable EA's SUDS retrofit projects to compete on an equal footing for Flood and Coastal Erosion Risk Management Grant in Aid funding.