Impacts of Seasonal Pumping on Stream Depletion

Visual MODFLOW was used for quantifying stream-aquifer interactions caused by seasonal groundwater pumping. Ahypothetical conceptual model was assumed to represent a stream-aquifer system commonly found in Korea. The modelconsidered a two-layered aquifer with the upper alluvium and the lower bedrock and a stream showing seasonal waterlevel fluctuations. Our results show that seasonal variation of the stream depletion rate (SDR) as well as the groundwaterdepletion depends on the stream depletion factor (SDF), which is determined by aquifer parameters and the distance fromthe pumping well to the stream. For pumping wells with large SDF, groundwater was considerably depleted for a longtime of years and the streamflow decreased throughout the whole year. The impacts of return flow were also examined byrecalculating SDR with an assumed ratio of immediate irrigation return flow to the stream. Return flow over 50% ofpumping rate could increase the streamflow during the period of seasonal pumping. The model also showed that SDR wasaffected by both the conductance between the aquifer and the stream bed and screen depths of the pumping well. Ourresults can be used for preliminary assessment of water budget analysis aimed to plan an integrated management of waterresources in riparian areas threatened by heavy pumping.Key words: Stream Depletion Rate (SDR), Stream Depletion Factor (SDF), Stream-aquifer interaction, Seasonal pump-ing, Visual MODFLOW