On the other hand when elevation of the groundwater table is lower than the elevation of the stream surface, water will flow from the stream to the aquifer. In this case, stream is feeding the aquifer and the stream is known as influent stream. Fig. 28.3 shows an influent stream. In some cases, the groundwater table is located below the channel bottom as shown in Fig. 28.4. In this case also, the stream feeds the aquifer and the stream is known as influent stream.

Fig. 28.4 Influent stream where GW table is below the bottom of the channel

Sometime a stream may act as an effluent stream as well as influent stream. Fig. 28.5 shows such a stream where on one side of the stream, the groundwater table is higher than the stream surface and on the other side of the stream, the elevation of the groundwater table is lower than the stream surface. Therefore, one side of the stream acts as an effluent stream and the other side acts as an influent stream.

Fig. 28.5 Influent-Effluent stream

The above discussion shows that the interaction of groundwater with stream/river has an important role in management of groundwater resources. Thus river plays an important role in solving groundwater management problem. One primary role of a river is that river acts as a constant head boundary condition in solving the groundwater forecasting problem. River also acts as the source of water which contributes water to the aquifer.