## Statistical analysis of observed flows

**Statistical analysis of observed flows** is the basic approach for estimation of flood-frequency relationship **when adequate data on observed flows are available**. If only a short record of streamflow is available, it is sometimes possible to establish a regional relationship with flows from neighbouring stations and to use such relationship to extend the existing short record in order to perform statistical analysis.

Application of flood frequency analysis is **limited to gauged catchments**, i.e. to gauged stream profiles. When flow rates of certain probability of occurrence are required at ungauged sites or along a stream (e.g. for flood zone mapping), other methods are needed for flood estimation.