WASUBI: a GIS tool for subbasin identification in topographically complex waterscapes

Spatially distributed modelling is dependent on segmentation of the underlying geographic data and the model output could be improved if relevant compartments are found and used. Herein, we present a method for identifying subbasins in complex topographic waterscapes. The method first finds local troughs and then expands them over a friction surface derived from bathymetry. Friction surfaces generated by different cost growth functions were tested, and shown to give consistent results. The model is sensitive to the quality of the underlying topographic dataset and its spatial resolution. WASUBI (WAterscape SUBbasin Identification) is written in ArcView's built-in scripting language, Avenue, and distributed as a program extension. The method is easy to use, only requiring a digital elevation model (DEM) and the user to give the number of basins to be generated. The segmentation method was tested against datasets covering the Finnish Archipelago Sea and the Okavango Delta in Botswana. Test results showed that the WASUBI delineated subbasins were more enclosed than subbasins created by a semi-random delineation method. The objectives of this study was to construct and critically test algorithms for subbasin identification, based only on readily available DEM data, for use in geographic information system modelling.