Surface-Water / Ground-Water Interaction

A stream, lake or other surface water body may either gain or lose water from the

ground-water system. In humid regions, the typical stream receives ground-water

discharge. A Gaining Stream is a stream which receives water from ground water

discharge. (Effluent stream)

If the water table is sloping toward a stream, the flow of water is toward the stream.

Contour maps can be drawn for the surface of a water table. A contour map of the

water table shows the level of equal elevation of the water table. In humid regions

the following generalizations can be made about the water table.

 1) A flat water table indicates the absence of ground-water flow.

2) A sloping water table indicates that ground-water is flowing.

3) Ground-water discharge zones are in topographical low areas.

4) The water table has the same general shape as the surface topography.

Gaining stream - water table contours "V" upstream.

Remember that this contribution of surface flow from ground water is known as baseflow.

Losing (influent) stream-Level of the stream is higher than the water table.

A stream that is normally gaining may become losing during a flood.

It is very difficult to separate ground-water flow from surface flow. One method is baseflow

separation. Another is by field measurements of infiltration rates of stream flow.

Streambed or lake seepage meter

Interaction depends on type of materials forming the bed of the stream.

Hydrograph from well WN-T2A completed in the stratified-drift aquifer near the North

Wellfield showing the typical duration of recharge and discharge phases of the annual

hydrologic cycle in a humid region.