Rivers also receive groundwater flow directly into the bed of the river. In many parts of Wisconsin the water table is above the level of rivers and lakes. Because groundwater flows from high to low just as surface water does, groundwater flows into most rivers. The groundwater that flows into a stream is called the stream s baseflow. Discharge is the amount of water a river is carrying.
Hydrologists measure discharge in units of volume per time, usually in cubic feet per second.
The amount of baseflow to a river is relatively constant over time, but is dependent on the regional water-table elevation, which can vary by several feet over one year. However, the discharge of a river varies over time, as the amount of overland flow changes. For example, after a rainstorm or during snowmelt, the amount of water running over the land to the river increases, and discharge of the river then increases. The discharge of a river depends on characteristics of the watershed, such as the number of acres, the amount of precipitation received, vegetation, soils, and slope. Rivers increase in discharge and size with increasing distance downstream.