Estimation of River Discharge

River discharge, the volume flow rate through a river cross section, is perhaps the most important single hydrologic quantity. It is a major link in the global hydrologic and geologic cycles and a critical component of climate, and represents the rate at which nature makes water available for human use and management. In the form of floods, it constitutes one of the most destructive natural hazards. Measurement of river discharge thus provides vital information for science and society. Measurement by conventional ground-based methods is expensive and is declining globally. Using various combinations of active and passive imagery and sensors mounted on satellites or aircraft, it is possible to obtain direct quantitative information on several hydraulic variables, including channel configuration and the area, width, elevation, and velocity of the water surface. Computations using conventionally obtained data indicate that this information can be used in various combinations with statistical models and topographic information to generate quantitative time- and location-specific estimates of discharge. Thus, it appears feasible to produce useful river-discharge information via remote sensing, especially for locations that are remote or otherwise difficult to observe conventionally. However, it is likely that this capability will be useful only for relatively large rivers and that, even for these, measurement accuracy will be considerably lower than is possible with ground-based measurements. Given the scientific and societal importance of river-discharge observations, and the present discharge-measurement network and unlikely prospects for its expansion, further development and testing of these approaches, development of concurrent sets of pertinent remotely sensed variables, and a more complete evaluation of the spacing and timing of observations possible with satellite systems is warranted. Keywords: river discharge; streamflow; discharge measurement; remote sensing; hydrologic cycle