Rivers are natural drainage channels. They collect runoff from precipitation and groundwater and discharge it into oceans or lakes. The main watercourse is determined by its water volume, length, or highest source. River size is determined by three factors: discharge, length, and drainage basin.
Discharge measurements
The global annual runoff into the oceans (38,500–44,200 km3/year) is dominated by runoff into the South Atlantic from eastern South America, into the western Pacific from east Asia, and into the Indian Ocean from India, and southeast Asia. Depending on the estimate, the Amazon alone accounts for 15–18% of the annual freshwater runoff into the oceans.
Water discharge may be expressed as mean annual discharge (denoted MQ), or as annual discharge (denoted Q). The units for measuring mean annual discharge (MQ) are m³/sec, and can be measured over a period of one or more years. The annual discharge (Q) is measured in units of km³/year. For large rivers, these values are difficult to measure (see ADCP), and they also vary considerably from year to year. The very large variation between low and high flow is often not apparent from the average runoff volume.
The discharge values shown in the tables below are mean annual discharge (units m/sec). To convert to annual discharge (units km/year) multiply by 0.031536.
List of rivers
Continent color keyAfricaAsiaOceaniaEuropeNorth AmericaSouth America
Ocean color keyAtlantic OceanPacific OceanIndian OceanArctic OceanEndorheic
No River name Averagedischarge(m³/s) Drainagearea(km²) Length(km) Outflow Notes, referencesPrimaryTributary