Regional flood methods

Estimation of peak flows on small to medium sized rural catchments is required for the design of culverts, small to medium sized bridges, causeways, soil conservation works and for various planning and regulatory purposes. Typically, most design flood estimates for projects on small to medium sized catchments are on catchments that are ungauged or have little recorded streamflow data. In these cases, peak flow estimates can be obtained using a Regional Flood Frequency Estimation (RFFE) approach, which transfers flood frequency characteristics from a group of gauged catchments to the location of interest. Even in cases where there is recorded streamflow data it is beneficial to pool the information in the gauged record with the RFFE information. A RFFE technique is expected to be simple, requiring only readily accessible catchment data to obtain design flood estimates relatively quickly. The RFFE method described in this chapter ensures that design flood discharge estimates are consistent with the gauged records and with results for other ungauged catchments in a region. It is recognised that there will be considerable uncertainty in estimates for ungauged catchments because of the limited number of gauged catchments available to develop the method and the wide range of catchment types that exist throughout Australia.