The Relationship between Groundwater and Surface Water

It is traditional to think of groundwater sustaining streamflows during the summer months, which indeed it often does. However, the interaction between groundwater and streamflow is complex and depends very much on local circumstances. Water naturally moves towards areas where faster flow is available and consequently can be drawn upwards towards a stream. This is the case in dry environments but is dependent on there being an unconfined aquifer near to the surface. If this is not the case then the stream may be contributing water to the ground through infiltration. 

Figure 1.

Figure 1 shows two different circumstances of interaction between the groundwater and stream. In Figure 1(a) the groundwater is contributing water to the streamflow as the water table is high. In Figure 1(b) the water table is low and the stream is contributing water to the groundwater. This is commonly the case where the main river source may be mountains a considerable distance away and the river flows over an alluvial plain with the regional groundwater table considerably deeper than stream level. 

Source : Tim Davie. 2002. Fundamental of Hydrology.New York : Routledge 270 Madison Avenue.