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

Lead Research Organisation: Imperial College London
Department Name: Civil & Environmental Engineering


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.


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Description This project considered the strategic role that SuDS play in management of environmental risk, with particular focus on flood risk to infrastructure. This was done using a cost-benefit analysis of SuDS retrofit schemes at a strategic (not single site) level. The SuDS mapping 'Adaptation Support Tool' (AST), developed by Deltares, was used to engage with stakeholders and co-create a set of intervention options. The wider SuDS benefits were assessed using a value transfer approach of the CIRIA's 'Benefits of SuDS Tool' (BeST), which encompasses the standard approach to flood risk appraisal by Multi-Coloured Manual (MCM) Handbook. The approach was applied to a test case study area, the Decoy Brook in Barnet, North London.

The research found that by including additional benefits such as amenity, rainwater harvesting, and surface water charges reduction, and adding net present values (NPV) to proposed solutions, the benefit cost ratio (BCR) increased considerably (by up to 200% in some cases compared to flood estimations only). Other additional benefits such as air quality, biodiversity, ecology and health, among others, were considered, but they accrued relatively low values.

It was found that in comparison to successful funding strategies implemented in other cities internationally, the UK lacks incentives to attract private capital investment for green infrastructure retrofitting, and centralised funding streams. In addition, surface water charge reductions are insufficiently generous in many UK regions, due in part to a lack of established 'parcel-based' charging system not being adopted by most water utility service providers.

The project showed that as part of planned strategic infrastructure provision, spend on mitigating environmental impacts on infrastructure using SuDS can effectively support multiple benefits. The work defined a replicable approach that can be transferred to generic guidelines for doing wider cost-benefit analysis at a strategic level. The case study indicates that the way towards wider scale SuDS retrofit is to split the investment among multiple stakeholders (including critical infrastructure owners) by highlighting the additional additional services for the same amount of investment.
Exploitation Route The three mechanisms provided innovation support to this project:

1. Co-design of the set of intervention option using the Deltares AST tool in the participatory stakeholder workshop. This formed the first step in the project defining the SuDS interventions to be used in the case study to address flood risk. This provided easy analysis of all input data in an engaging process of SuDS mapping, and produced a set of solutions based on stakeholders' knowledge of the case study and desired outcomes.
2. The team then used CIRIA's BeST tool for wider SuDS appraisal implemented for the case study. Use of this tool provided additional criteria to assess the project against additional criteria that are not conventionally used in SuDS economic appraisal; such as amenity, air quality, biodiversity, ecology, etc.
3. The team followed this up with analysis of cutting edge funding strategies, including direct and direct incentives and parcel-based surface water charging systems, which are used to support the implementation of SuDS interventions worldwide. These were tested to the UK's flood and water management conditions to understand where it was possible to move forward in the promotion of SuDS more widely in the UK.

Bringing these three steps together represents the most innovative part of this project by addressing issues that are repeatedly highlighted by stakeholders as being the biggest obstacles to SuDS large-scale adoption and implementation in UK. By following the proposed methodology, the profile of SuDS can be raised as an essential part of creating a self-sustaining, extreme weather resilient and healthy urban environment.
Sectors Environment

Description This project has resulted in the production of an internal report containing detailed analysis of two scales of flood risk management scheme that were applied to protect critical infrastructure in the case study region. The report will be used as part of the Environment Agency evidence base to support broadening funding streams and promoting strategic level Sustainable Drainage Systems.
First Year Of Impact 2016
Sector Environment
Impact Types Policy & public services

Description Community Water Management for a Liveable London (CAMELLIA)
Amount £4,079,082 (GBP)
Funding ID NE/S003495/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 01/2019 
End 12/2023
Description 2016 EGU General Assembly 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The results of the work will be presented as an oral presentation at 2016 EGU General Assembly in April. It is expected that the presentation will generate further discussion about the topic and potential international collaborations.
Year(s) Of Engagement Activity 2016
Description BHS National Meeting on Impacts of Flooding on Critical Infrastructure: Stakeholder-Oriented Approach 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact The joint presentation by project PI and project partner EA was done for the academic and business audience, followed by the discussion panel that generated discussion about the application of green infrastructure in cities.
Year(s) Of Engagement Activity 2015