watersheds

A watershed, drainage basin, or catchment is the land area whose rainfall and other precipitation drains into a common outlet, such as a river, lake, or coastal point. The boundary of a watershed is defined by topography—the drainage divide. Watersheds include surface water bodies, wetlands, soil moisture, and groundwater that supply flow to the outlet.

The size ranges from a few hectares in small streams to continental-scale basins spanning thousands of square kilometers. The internal flow path may involve streams, rivers, and aquifers; hydrology is governed by precipitation, evapotranspiration, infiltration, percolation, runoff, and storage in soil and rock.

Land cover and human activity strongly influence watershed behavior. Forests and wetlands reduce runoff and sediment, while urbanization and agriculture can increase impervious surfaces, accelerate runoff, transport nutrients and pollutants, and alter groundwater recharge.

Watershed management adopts an integrated approach to protect and improve water quantity and quality, reduce flood risk, and sustain ecosystems. Practices include land-use planning, riparian buffers, erosion control, stormwater management, restoration projects, and monitoring.

Agencies monitor discharge and rainfall, maintain gauges, and use models and GIS to analyze watershed response and forecast flows. Watersheds support habitat for aquatic and terrestrial species and provide essential services such as drinking water, irrigation, and recreation.