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Tender Invitation: Natural Flood Management Modelling — Trent Rivers Trust and The Rivers Trust

Background & study area The Trent Rivers Trusts are delivering targeted NFM in the Soar catchment (1400 km²) as part of a strategic project funded by Aviva Insurance and WWF. One of the aims of the project is to investigate modelling approaches that would allow both RMAs and CaBA partnerships to estimate the appropriate level of FCRM funding for each catchment based on estimates of damages avoided. This funding, blended with other sources of money for other ecosystem services, could be used to plan the delivery of NFM in each catchment. The problem The literature supports an estimate of the hydrological benefits of NFM between 1% and 10% depending on the size of the catchment; the spatial distribution of NFM; the antecedent soil moisture conditions; the shape and intensity of the storm and the availability of NFM opportunities. A recent project managed by The Rivers Trust attempted to model the number of properties removed from flood risk based on the predicted spatial pattern of future NFM. The Project Board, made up of academics and flood professionals from the insurance industry, Environment Agency, Water Company and eNGOs, concluded that while fully distributed modelling was possible the conclusions were highly uncertain and still relied on assumptions about the availability of NFM opportunities that can only be validated by extensive engagement with landowners. An alternative approach was recommended by the Project Board which would provide the main stakeholders with acceptable estimates of the level of NFM that could be justified by the potential FCRM benefits for each catchment. The majority of the CaBA movement already uses the Working With Natural Processes (WWNP) datasets which highlight the potential level of NFM opportunity within each catchment for creating storage and planting trees. However, this data does not help partnerships prioritise which NFM opportunities will have the greatest impact on peak flows in specific locations. A number of similar approaches have been used across the country, based on time of travel analysis, to target the locations for NFM so that they have the maximum impact on reducing flood risk. In the Soar catchment the local trust has used SciMap Flood to do this analysis because it allows users to specify the flooding hotspots of interest and then locate the best locations for NFM which will have the most benefit for all of the communities of interest. This analysis, coupled with the WWNP, allows the trusts to select the NFM opportunities that will have the greatest benefit for the communities at risk. A catchment-based approach to delivering the right NFM in the right place is now possible, with the trust able to engage the landowners who can potentially make the most difference. The next piece of evidence that the partnership need to understand is: What scale of NFM is justified by the potential damages avoided due to NFM? Fully distributed modelling is expensive and still highly uncertain. Ideally this project will develop and test a methodology which uses industry standard tools and approaches to create outputs that enable key stakeholders in flood risk management and reduction to confidently invest in an appropriate level of NFM for the Soar catchment. The proposal The consultant is asked to provide a proposal for the Soar catchment which could be used to estimate the potential damages avoided if opportunities for NFM are implemented across the catchment. Your proposal should specify: Which model you propose to use and how this model will be accessed. The Environment Agency are aware of this project and will facilitate access to the data and models required. Approaches based on existing credible models of the Soar catchment are likely to score more highly because the results will be consistent with existing FCRM outputs which will build confidence in the investor community. How will you estimate and then incorporate the hydrological impact of NFM within the model? Ideally explaining how the method will incorporate more than just the provision of additional online or offline storage.How will you convert the modelled change in peak flow into damages avoided?What outputs will you be able to produce within the indicative budget and timeframe?How reliable are the outputs for estimating the appropriate level of investment from the flood management and risk reduction community?Could this approach be scaled so that similar maps could be produced for each catchment which would help partnerships plan the level of NFM investment which is justified by the flood benefit alone? If the approach could be incorporated within the EAs NAFRA 2 modelling program in the future that would also score the proposal highly. Please send a completed tender to David.​johnson@​theriverstrust.​org by midday 4th March 2024. The proposals will be judged against the following criteria: Cost. 30%Technical credibility with the buyer community. This includes the RMA and the insurance industry. 40%Ease with which the approach could be rolled out across the country to provide a strategic output that could be used by CaBA partnerships. 15%The team proposed to do the work. 15% Budget The indicative budget is up to £40,000 including VAT. The project will be funded by Trent Rivers Trust but jointly managed by The Rivers Trust and Trent Rivers Trust. Timescale The project will start at the beginning of April 2024 and be completed by the end of July 2024. An interim report at the end of June 2024 should enable the project team at Trent RT to incorporate the key learnings.

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