catchments

A catchment is the geographic area of land where precipitation collects and drains to a common outlet, such as the mouth of a river, a lake, or a reservoir. It is defined by the surrounding topography, which directs water toward the chosen outlet. In many contexts, catchment and drainage basin are used interchangeably, but catchment can emphasize the land area contributing runoff to a specific outlet within a larger hydrological system.

Water within a catchment follows several pathways. Precipitation may become surface runoff, infiltrate the soil to become groundwater, or be lost through evapotranspiration. Water stored in rivers, lakes, and wetlands can delay and regulate flow. The balance among these processes depends on climate, soil properties, vegetation, geology, and human activities such as urbanization, agriculture, and reservoir operation.

Delimiting catchments involves identifying watershed divides, typically along ridges, to determine which areas drain to the same outlet. Delineation often uses digital elevation models and hydrographic data. Key metrics include catchment area, drainage density (the total length of streams per unit area), and stream order, all of which influence hydrological response and flood behavior.

Applications of catchment analysis include water resources planning, flood risk assessment, environmental and land-use management, and ecological studies. Data are gathered from rainfall and discharge measurements at gauging stations, streamflow records, and land-use maps, and are interpreted through hydrological models to understand runoff generation, storage, and transport within the catchment.