Understanding drainage density is fundamental in hydrology. Drainage density, defined as the total length of streams per unit area, provides insight into the efficiency of water movement within a catchment. High drainage density suggests steep terrain, impermeable surfaces, or high precipitation rates, leading to quicker runoff. In contrast, low drainage density is associated with flatter landscapes and permeable soils, resulting in slower drainage.
In this tutorial, we will use QGIS to calculate drainage density for a catchment area. We’ll explore two approaches: a straightforward calculation using polygon and line geometries in the Field Calculator, and a spatially distributed method using the Line Density tool. By the end of this tutorial, you’ll be equipped to derive drainage density maps that are invaluable for hydrological studies, land-use planning, and environmental management.