A GIS-approach for determining permanent riparian protection areas in Mato Grosso, central Brazil

In this paper we propose a DEM-based GIS methodology for the identification and delimitation of riparian protection areas according to stream width. In Brazil, vegetation cover in buffer zones is monitored by mid-resolution satellite imagery, so our methodological approach includes procedures to ensure geometrical accuracy for multiple spatial layer overlay. For a study area in Mato Grosso, a sequence of DEM pre-processors was used to hydrologically correct a SRTM 90 m resolution digital elevation model. Then samples of river widths were obtained by measures using high-resolution IKONOS imagery and regressed against watershed contribution areas to define protection zone buffers. We propose a procedure to attribute the DEM-based width estimates derived from topographic maps and satellite imagery to the river networks. Validation using high-resolution IKONOS imagery indicates that the proposed methodology produces RMS errors of about 20 m on average for watercourses up to 600 m wide. This is a considerable improvement in protection area delimitation compared with current practice, particularly in headwater regions and along streams with widths of up to 200 m. Accuracy assessments indicate that environmental licensing procedures should include a tolerance of between 48% (<50 m) and 15% (200–600 m) of stream width, according to systematic errors included in the estimates.

► SRTM DEM allows reliable river channel width estimates from less than 10 m up to about 600 m.
► Contribution area size explains more than 94% of the variation in cross-section widths with a RMS error of about 20 m. Reach classification achieves an overall accuracy higher than 85%.
► A GIS-procedure is proposed to attribute width estimates to the river networks derived from topographic maps and satellite image interpretation.
► Accuracy assessments shows that reach width estimates should include a tolerance of between 48% (<50 m) and 15% (200–600 m) if used for buffer designation of permanent protection areas in environmental licensing.