Effluent or gaining streams occur when the adjacent water table and groundwater head beneath the stream are greater than the stream stage (Figure 4, Figure 16). Groundwater gradients are upward (Figure 16a). In map view, groundwater flow converges towards the stream and equipotential lines point upstream as a “V” (Figure 16b). Groundwater entering the stream becomes streamflow and the stream stage represents the water table elevation at the edge of the stream.
Figure 16 – Cross section and map views of effluent groundwater-stream interactions (gaining stream). Equipotential lines and relative head values are shown as blue water table contours. Groundwater flow is in the direction indicated by blue arrows. Aquifer conditions are assumed to be isotropic and homogeneous. Monitoring wells are open only at the bottom. a) Cross section showing upward groundwater gradient and groundwater discharging to the channel (Woessner, 2018). b) In map view, equipotential lines cross the stream and point in the upstream direction (V points upstream). The approximate location of the cross section in Figure 16a (C-D) is the dashed black line located along flowlines that converge at the stream (after Healy et al., 2007).
