Watershed slope length mapping with Geographical Information System

Abstract

Procedures for the generation of slope length images by geographical information systems (GIS) are presented. The geoprocessing methods were evaluated through regression analyses of the digital results with a cartographically hand-measured data set, measured in a regular grid of 200m spacing, covering São Joaquim watershed (Pirassununga, SP). Anisotropic cost analysis function of SIG was adapted to model the slope length, by exploring the conceptual similarity and the analogy between its elements and topographic features. The extraction steps of the images from the Digital Elevation Model (DEM), hilltops, slope direction, slope force and unitary distance, as well as the whole developed procedures, were programmed in an internal file of the specific GIS language. Errors in the slope length estimation were shown to prevail in areas of steep relief, with high slope angles and short slopes, which suggest the need of research for the establishment of adequate fit techniques for GIS functions