WATERSHED DELIENATION IN Q GIS USING GRASS TOOL BY GEOTECH SOLUTIONS скачать в хорошем качестве

WATERSHED DELIENATION IN Q GIS USING GRASS TOOL BY GEOTECH SOLUTIONS

Watershed delineation in QGIS using GRASS (r.watershed) involves processing a filled Digital Elevation Model (DEM) to determine flow direction, flow accumulation, and subbasin boundaries. Key steps include setting a threshold for minimum watershed size and using r.water.outlet for specific points, crucial for hydrological modeling, flood risk management, and resource planning. Steps for Watershed Delineation in QGIS using GRASS Preparation: Load a DEM into QGIS, ensuring it is projected (e.g., UTM) to enable accurate distance/area calculations in meters. Fill Sinks: Use r.fill.dir (GRASS) or r.fill.dir to remove depressions (sinks) in the DEM that block flow, as shown in this YouTube video. Run r.watershed: Open the Processing Toolbox, search for r.watershed, and select the filled DEM as the elevation input. Minimum size of exterior watershed (Threshold): Defines the smallest catchment size (in pixels). A smaller number (e.g., 500-1000) generates more detailed subwatersheds, while a larger number (e.g., 10,000) creates fewer, larger basins, as explained in this YouTube video. Output: Generates flow accumulation, drainage direction, and basin maps. Define Outlet (r.water.outlet): Identify the point of interest (e.g., a river gauge) and use r.water.outlet with the flow direction raster to define the specific catchment area. Vectorization: Convert the resulting raster watershed into a vector polygon using r.to.vect for further analysis