Options to Select Rain Gauging Stations when Modelling Streamflow for Water Resources Management

Abstract

Conversion of point rainfall measurements as areal rainfall is one of the key factors that should be carefully considered during streamflow modelling. Research publications indicate that distribution of gauging stations influences the representativeness of spatially averaged rainfall. Many guidelines provide contrasting recommendations and hence available literature is inadequate to provide specific guidance on the appropriate number of gauging stations, density and averaging method. Past research emphasises that high station densities do not always provide the best streamflow estimates, and point to a threshold density range between 2.6 and 2442 km(2)/ station. Ongoing modelling practices reflect that the median station density values used respectively for small, medium and large catchments are 19, 117 and 470 km(2)/ station. The most rational option is to select a suitable station density considering both time-tested guidelines and median values as appropriate for watershed size. Commonly used spatial averaging methods are the Arithmetic Average, Thiessen, Kriging, IDW and Spline. Past studies point out that the best is to capture the most contributing stations by optimising the station influence using modelled streamflow.