Abstract
Two field experiments were conducted to investigate the effect of the capillary fringe on surface water-groundwater interactions and on streamflow generation in a shallow water-table aquifer. The results from both experiments showed that the water-table adjacent to the stream, where the capillary fringe extended to or close to ground surface, responded rapidly to the precipitation events due to the initially low storage capacity of the medium. This rapid and large response led to the development of a water-table mound on both sides of the stream and flow nets showed that the mound resulted in the discharge of pre-event water through the seepage faces that developed on both sides of the stream. Furthermore, the mound contributed to the discharge of event water in that precipitation falling on the seepage faces was transported directly to the stream as overland flow. A further contribution of event water to the stream occurred as surface runoff from areas upslope of the seepage faces, where the pressure head was zero, but the rainfall rate exceeded the infiltration capacity of the soil. Under the conditions of the study, the results support the commonly recognized mechanisms of streamflow generation, including the partial area, variable-source-area overland flow, and variable-source-area subsurface flow concepts. The relative contribution of these mechanisms to stormflow appeared to be determined by the response of the capillary fringe. The amount of pre-event water in the discharge determined by the tracer method of hydrograph separation showed good agreement with the instantaneous pre-event discharge hydrograph determined from flow nets.
Published Version
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