Where, P is the precipitation on the area supplying the aquifer, Q_s is the surface stream flow over the same area, E_T is the evapotranspiration, Q_g is the net ground water inflow to the area, ΔS_g is the change in ground water storage, ΔS_s is the change of surface storage. All the terms, except precipitation of in Eq. (28.1) are subjected to artificial change.

Stream-aquifer interaction

Fig. 28.2 effluent stream

River, in general contributes water to the adjacent phreatic aquifer. The low water flow in a river is nothing but the contribution of groundwater from the adjacent aquifer. The low water flow in a river is also known as the base flow of the river. In this case, the elevation of the groundwater table is higher than the elevation of the stream. When groundwater is feeding a river, the stream is known as effluent stream.

Fig. 28.3 Influent stream