The government has published new guidance on calculating the impact of flood and coastal erosion risk management schemes on the natural and historic environment. There is also a tool to calculate a monetary value of the impact.
EHOV (Environment and Historic Environment Outcome Valuation) is an update to the 2010 Economic Valuation of Environmental Effects (EVEE) guidance. This guidance comes with a tool called EHOV-Lite and look-up tables.
You can use this guidance and the EHOV-lite tool, if you think your project will have significant impacts which the tool can help value.
The guidance references the best sources of data on environmental and heritage values and also explains how to apply them in the context of a flood project.