The study modelled current and future flood risk from both rivers and surface water, including tidally influenced river reaches. It also considered and brought together modelled housing/industry growth projections and climate change scenarios to attempt to understand the impact of flood risk now and into the future. The studies geography spans three significant river catchments; the Nene, the Great Ouse and the Thames. A flood risk modelling approach was needed that would provide sufficient local detail but that could be applied and analysed on a regional scale.
Existing in-channel water level data was combined with representative hydrograph profiles in a full hydrodynamic floodplain model. Peak water levels were identified from the State of the Nation Database (SoN 2018) and were used to provide a consistent set of levels across the study area. An industry standard 2D hydraulic model was used to represent how floodwater spreads across the floodplain. Verification checks with local models (where available) did identify some inconsistencies, however, for the purpose of this regional scale study the SoN water levels were considered adequate. It should be noted that the flood modelling approach taken is suitable for economic analysis only, this is due to the number of assumptions made to allow for the large geographical scale modelled.
Four types of flood risk interventions were considered: flood storage, Natural Flood Management linear, defences (NFM), and property level resilience (consisting of a generic combination of flood gates, non-return valves, and airbrick covers). Specific planned interventions were not considered. It should also be noted that this study is wholly desk based and as such deliverability testing of these interventions within the study area has not been undertaken.