Sky Lake water level data, 2016-2018, Humphreys County, Mississippi

Lake stage, wetland stage, and groundwater levels in 11 wells collected by Michael C. Gratzer at the University of Mississippi Department of Geology & Geological Engineering. Data used in the following with abstract below: Gratzer, M.C., Davidson, G.R., O'Reilly, A.M., and Rigby, J.R., (in press 12/2019), Groundwater recharge from an oxbow lake-wetland system in the Mississippi Alluvial Plain, Hydrological Processes, https://doi.org/10.1002/hyp.13680

The Mississippi River Valley Alluvial Aquifer ranks among the most over-drafted aquifers in the United States due to intensive irrigation. Concern over declining water levels has increased focus on understanding the sources of recharge. Numerous oxbow lakes overlie the aquifer which are often considered hydraulically disconnected from the groundwater system due to fine-grained bottom sediments. In the current study, groundwater levels in and around a 445-ha oxbow lake-wetland in Mississippi were monitored for a two-year period that included an unusually long low-water condition in the lake (>17 months), followed by a high-water event lasting over four months before returning to earlier low water levels. The high water pulse (>4 m rise) provided a unique opportunity to track the impact in the underlying alluvial aquifer. During low-water conditions, groundwater flowed westward beneath the lake. Following the lake rise, groundwater beneath and near the perimeter responded as quickly as the same day, with more delayed responses moving away from the lake. Within two months, a groundwater mound formed near the center of the oxbow (>3 m increase), with a reversal in the local hydraulic gradient toward the east. Flow returned to a westward gradient when the lake level dropped back below 0.3 m. Analysis of precipitation and nearby river stage could not account for the observed behavior. Recharge to the aquifer is attributed to rising water levels spreading over point bar deposits and into surrounding forested wetlands where preferential flow pathways are likely to exist due to buried and decomposing tree remains. An earlier study in the wetland demonstrated increasing redox potential in isolated zones, consistent with the existence of preferential flow pathways through the bottom sediments (Lahiri & Davidson, this issue). Retaining high water levels in oxbow lakes could be a relatively low-cost water-management practice for enhancing aquifer recharge.