Identifying A Mechanism For An Infiltration Threshold From The Sunflower River, MS To The Underlying Alluvial Aquifer

Author(s): Patton, A.; Davidson, G.; Rigby, J.; Barlow, J.

Long-term groundwater level and river stage measurements at a USGS coupled groundwater stream-gaging station located on the Sunflower River at Sunflower, MS show an apparent stage-threshold for infiltration to the underlying alluvial aquifer. This site is located near the center of a large regional cone of depression in the Mississippi River Valley alluvial aquifer and therefore provides insight into the effects of groundwater declines on streamflow in the Big Sunflower River. Groundwater levels respond to changes in river stage only when river stage exceeds 34 m msl (mean sea level). The purpose of this research was to identify the responsible mechanism. Two hypotheses were considered: (1) scour of infiltration-limiting fine-grained bottom sediments during high flow rate events at higher stage, and (2) lateral infiltration at high stage into more permeable coarser grained sedimentary layers intersecting the stream channel at higher elevation.

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