Explanatory Note for FD2320 and FD2321
Supplementary Note on Flood Hazard Ratings and thresholds for development planning and control purpose - Clarification of the Table 13.1 of FD2320/TR2 and Figure 3.2 of FD2321/TR1. EA and HR Wallingford, May 2008.
http://randd.defra.gov.uk/Document.aspx?Document=FD2321_7400_PR.pdf