The total amount of sediment exported from a drainage basin over a given time period, measured at the basin outlet. Sediment yield integrates all erosion, transport, and deposition processes within the watershed.
Sediment yield is the quantity of sediment that passes a measurement point (typically the basin outlet or a gauging station) over a specified time period, usually expressed as a mass per unit area per unit time (tonnes/km²/year). It represents the net result of all erosion processes operating within a watershed minus the sediment stored in transit through deposition on floodplains, in channels, and behind dams. The sediment delivery ratio (SDR), defined as the ratio of sediment yield to gross erosion within a basin, is typically well below 1.0 (often 0.01-0.30), indicating that a large fraction of eroded material is redeposited before reaching the outlet. Sediment yield varies dramatically across the globe, from less than 10 t/km²/yr in stable, vegetated shield areas to over 10,000 t/km²/yr in tectonically active, semi-arid mountain regions such as the Loess Plateau of China. Suspended sediment concentration and discharge measurements at gauging stations are the primary method for estimating sediment yield, with rating curves relating sediment transport to water discharge. Reservoir sedimentation surveys provide complementary long-term sediment yield estimates. Human activities including deforestation, agriculture, mining, and urbanization have dramatically increased sediment yields in many basins, while dam construction has reduced downstream sediment delivery, causing coastal erosion and delta retreat in many regions.