A flood risk assessment is a technical study identifying the sources, probability and consequences of flooding at a location, and setting out how a proposed development responds to that risk. It is carried out in stages, from an initial screening through to a detailed assessment with hydraulic modelling where necessary.
The guidelines set out a staged approach. Stage 1 is a screening exercise to establish whether flood risk may be an issue. Stage 2 is an initial assessment using available mapping and records. Stage 3 is a detailed assessment, which may involve hydraulic modelling to establish flood levels for defined return periods and to test the effect of the development.
For a single house the work is usually proportionate: a competent engineer reviews national and local flood data, surveys site levels, establishes design flood levels and recommends floor levels, access arrangements and drainage measures.