Variably Saturated Flow between Streams and Aquifers

The influence of unsaturated media on stream infiltration has been examined through a series of numerical solutions of combined saturated-unsaturated (variably saturated) flow in simple stream-aquifer systems. System behavior is analyzed largely in terms of response to declines in local water table level, presumably as a result of increased pumping on regional basis. The simulations, all of which are of a generic nature, are roughly based on existing and possible future conditions in the Mesilla Valley portion of the lower Rio Grande Valley in south-central New Mexico. Emphasis is placed on cases in which a zone of unsaturated material lies between the stream and the underlying water table. Under this set of conditions, the stream and aquifer are described as being disconnected. Factors that strongly affect the disconnection process include streambed clogging by fine-grained materials and aquifer heterogeneity. When disconnected, a stream-aquifer system with a shallow water table behaves quite differently from one in which the water table is deep. Differences between these two cases, as well as with other stream-aquifer situations, are distinctly manifested in hydraulic head and moisture content distributions, pressure head profiles, system fluxes and water table behavior.