Evolution of stream-aquifer hydrologic connectedness during pumping – Experiment

SummaryThe evolution of the hydrologic relationship between streams and aquifers resulting from groundwater pumping (or drainage) near a stream is of great interest to the research community and to water management decision makers. A stream-aquifer-ditch sandbox was built to be used to characterize the hydrologic connectedness of the stream-aquifer responding to declines of the water table over a vertical profile, presumably as a result of increased pumping near the stream. We called the position of water table over the vertical profile the water table curve. Six hydrologic cases were chosen to investigate the behaviors of the water table curve. All cases are roughly based on existing and possible real hydrogeological conditions in nature. Emphasis was placed on the analysis of the dynamic processes of evolution in the stream-aquifer system where the stream-aquifer changes from a fully connected condition to a disconnected condition. The experimental results for the six cases were shown by differences in hydraulic head contours, pressure head distributions and the shapes of the water table curve over a vertical profile, the thickness of the inverted saturated zone, and the induced recharge of groundwater from the stream. Factors that strongly affect the evolution of stream-groundwater relationships are discussed including changes in stream stages, the declines of the water table curves, stream geometries, streambed clogging and aquifer heterogeneity. Then a new concept of a disconnected stream with aquifer is given according to the evolution of stream-groundwater relationships.

► We built a sandbox to simulate stream-aquifer interactions due to pumping.
► We analyzed the hydrological disconnection processes for stream-aquifer systems.
► The disconnection process was controlled by a number of hydrological factors.
► When disconnected, an inverted saturated zone commonly occurred below streambeds.
► The inverted zones and unsaturated zones have complex shapes and varied thickness.