One of Argyll's consultants is an ex-employee of Ambiental. They have lots of experience in doing Flood Risk Assessments (FRA) and wanted to fill in our background knowledge on what this involves.
An FRA is carried out when planning permission is being sought for a property within a flood zone. Each case is considered separately and the local authority along with the Environment Agency need to be convinced that it is a valid plan.
Detailed flood data must be requested from the EA. It is not the standard data that is released for general use (due to some copyright reason). It is also necessary to keep the EA on your side as they will be giving their individual opinion on the planning permission.
The FRA will support the planning request by including mitigation advice. The most important thing being looked for is whether the occupants can escape in the event of a flood. The exact plan will differ depending on local authority. Something near the Thames can generally get away with saying that the occupants can go upstairs and wait for the (tidal) floodwater to recede. Othe areas of the country might require a special gantry to be constructed.
If a property is going to increase the risk of flooding elsewhere, then mitigation must be planned. Voids under the new building, grassgrids for hard standing, run-off channels, etc.