Water Resources Research Act Program

Details for Project ID 2013TN102B

Re-filling the Bucket: Recharge Processes for the Memphis Aquifer in the Exposure Belt in Western Tennessee

Institute: Tennessee
Year Established: 2013 Start Date: 2013-03-01 End Date: 2015-02-28
Total Federal Funds: $16,977 Total Non-Federal Funds: $30,627

Principal Investigators: Brian Waldron, Daniel Larsen

Project Summary: Little is currently known regarding direct recharge to the Memphis aquifer across the unconfined region in western Tennessee; however, initial investigations indicate that little recharge may penetrate through the upland surfaces, taking possibly 100 years to move from the ground surface down to the water tableGaining an understanding of recharge processes in the unconfined region of the aquifer is critical to understanding input rates both spatially and temporally so as to ascertain the impact of land use and climate change and ultimately effect the long-term sustainability of this valuable and heavily relied upon natural resource. The proposed project will investigate recharge processes in the unconfined region of the Memphis aquifer at the Pinecrest site, near LaGrange, Tennessee. Initial investigations have included using vadose-zone and saturated zone chloride mass balance methods (CMB) to estimate recharge in the upland region (i.e. thick vadose zone), installation of and continuous water level monitoring in an observation well on an upland surface screened within the Memphis aquifer, and recurrent analyses of vadose zone soil moisture profiles within one of the wells using a neutron probe. Furthermore, geologic mapping and reconnaissance soil studies have clarified geologic and soil control on recharge processes. Where prior investigations at the site indicated a slow (~100 yrs) migration of infiltrated water through the vadose zone in the upland region, it is hypothesized that seasonal recharge occurs along the hillslopes, gullies, and stream valleys. These areas are underlain by a thin veneer of silty colluvium overlying mildly weathered, unconsolidated sand of the Memphis aquifer; thus, expediting the recharge process. The upland gully systems, which are distant from perennial streams, are thought to be most significant because the infiltrated water is likely to follow a deeper flow path in the regional aquifer system. This deep recharge does not discharge back into the local streams but rather provides regional recharge to the aquifer. Hence, testing this hypothesis will clarify which parts of the regional landscape are most significant for recharge; thus, greatly advancing our understanding of recharge to the Memphis aquifer and sustainability of its water resources. Project implementation will require monitoring soil moisture and infiltration along a hillslope and into the adjacent stream valley. Additionally, ground water level conditions will be monitored in wells on upland, hillslope, and valley sites and stream flow monitored along the stream channel. We will install two shallow monitoring wells in the upland stream valley and one along the hillslope. Clusters of piezometers and lysimeters will be installed along a transect from the upland hilltop down to the stream valley. Water levels will be monitored by a network of pressure transducers in new and existing wells. Lysimeters and neutron probe readings from within the hillside piezometers will characterize soil moisture and hillslope recharge. A Parshall flume will be installed in an upland stream to measure surface water discharge during rain events and potential flow of the stream during the wet season as a means of calculating a mass balance. Water chemistry data from ground water, soil water, and the stream water will be used to estimate soil water and stream water components in the ground water. A weather station will be installed to record precipitation and other climatic information needed to estimate evapotranspiration.