The classification of hydrologically homogeneous regions

With the operation and maintenance of streamgauging networks in many develo ping countries coming under increasing pressure through lack of funds and s uitably trained personnel, greater reliance must be placed on procedures fo r transferring information from gauged to ungauged catchment areas. These a pproaches to generalizing hydrological variables, such as the quantiles of the frequency distributions of floods and low flows, are collectively refer red to as regionalization methods. An important feature of these methods is the demarcation of hydrologically homogeneous regions. The latter may be r egarded as an example of the wider problem of classification of data sets, for which a variety of modern informatic tools, such as artificial neural n etworks and fuzzy sets, may be invoked. Application of examples of these te chniques to flood data for the southwest of England and Wales has demonstra ted that classes may be defined by Representative Regional Catchments (RRCs ), whose characteristics are hydrologically more appealing than those impar ted merely by geographical proximity. The techniques employed, Kohonen netw orks and fuzzy c-means, are straightforward in application, and were found to identify broadly similar RRCs. The results indicate the feasibility of e mploying these methodologies on a country-wide basis.