streamflow

Streamflow is the rate at which water flows through a river or stream, typically expressed as discharge (Q) in cubic meters per second or cubic feet per second. It represents the integrated result of precipitation, runoff, groundwater exchange, and storage within a watershed. Streamflow varies with time and location, reflecting climate, season, watershed characteristics, and human influences such as reservoirs and diversions.

Streamflow is commonly measured at gauging stations that record water level (stage) and convert it to discharge using a rating curve. Other methods include weirs, flumes, and tracer techniques. The recorded data are used to construct hydrographs (discharge versus time), flow duration curves, and seasonal or annual statistics.

Flow regimes describe typical patterns: perennial streams flow year-round; intermittent streams have periods of no surface runoff; ephemeral streams may flow only briefly after rainfall. Hydrographs show the rising limb, peak discharge, and recession to baseflow. Baseflow is the portion sustained by groundwater; stormflow is the response to rainfall.

Key controls are precipitation, snow and ice melt, soil moisture, evapotranspiration, and groundwater recharge. Land cover, soil properties, and watershed drainage influence infiltration and runoff. Human activities—dam releases, reservoir storage, groundwater pumping, and urbanization—alter magnitude and timing.

Streamflow data underpin water resources management, ecological flow assessments, flood forecasting, nutrient and sediment transport studies, and reservoir operation. Data are maintained by agencies such as the US Geological Survey and Environment Agencies; international programs compile global datasets.