RECHARGE OF THE MEMPHIS AQUIFER IN AN INCISED URBAN WATERSHED

The Memphis aquifer is the most important source for groundwater in western Tennessee; however, recharge processes to the aquifer are poorly understood. Previous studies have shown that in rural areas recharge to the aquifer occurs more efficiently in stream gullies with sand bottoms than in upland terraces. The same is expected in urban streams where the Memphis Sand is exposed in gullies and adjacent upland areas have substantial urban land use. Water balance research in Sandy Creek in Jackson, Tennessee, provides information regarding infiltration and potential recharge to the Memphis aquifer that may be typical of urban stream valleys where sandy Coastal Plain aquifers are exposed.

In the present study, hydrologic data from Sandy Creek has been collected since February 2016. The hydrologic analyses include grain-size analysis of soil and sediment, soil-water analysis by tensiometer, lysimeter and neutron-probe moisture measurements, discharge estimates using stage-discharge relationships, as well as weather data from an on-site weather station. Preliminary data show that the upper reach of Sandy Creek is ephemeral. Discharge is present only during storm events and stream flow rapidly dissipates following precipitation events due to infiltration into the stream bed. Soil moisture data indicate a seasonal shift in water retained in the soil column, with peak soil water storage during winter to early spring and steady drying through the late fall. Monthly water balance estimates in the watershed indicate peak groundwater recharge during winter and early spring months with lesser contributions during the summer and fall. Most of the recharge is attributed to discharge losses in the drainage basin, with little recharge passing through the silt-rich soils of the upland surfaces. The recharge data from Sandy Creek are similar to those from a rural recharge study in western Tennessee, supporting the importance of upland-stream discharge loss for recharge to the Memphis aquifer. Given the propensity for decrease in permeability during soil development on Coastal Plain deposits in the southeastern U.S., recharge from discharge losses in upland streams incised through sandy Coastal Plain deposits may be more important than previously thought for supporting groundwater resources in down-gradient aquifer systems.