Streams gain water from inflow of groundwater through the streambed. For groundwater to discharge into a stream channel, the altitude of the water table in the vicinity of the stream must be higher than the altitude of the stream bed. Opposite of influent stream.
Why is an effluent stream important?
As groundwater discharges into the stream abstraction of groundwater in the immediate vicinity of the stream could result in reduced stream flow. During dry or low flow periods groundwater can be the only source of the water feeding the hydrological system.