Characterizing Surface Water/Ground Water Interactions with Ground Penetrating Radar Grant uri icon

abstract

  • Water demand in North Carolina will increase as the population expands from 8 million (2000) to the expected 12.5 million in 2030 (Tillman 2004). In the Tar River Basin residents rely on both ground water and surface water and it is estimated that water demand in the Tar River basin will increase by 55% between 1997 and 2020 (North Carolina State Water Supply Plan 2001). Ground water supplies have traditionally been extracted from the Black Creek and Upper Cape Fear aquifers. Naturally slow recharge rates and increased ground water withdrawals over the last 25 years have resulted in the decline of piezometric levels from 2 to 8 feet per year. Aquifer withdrawals have restilted in less upward movement of ground water to discharge areas and aquifer dewatering (Lautier 2001). Water supplies are critical to the economic well-being of North Carolina's Coastal Plain, yet few studies detail the river-ground water relationships that exist here. Published piezometric and ground water surface data are rarely available near rivers and it is commonly assumed that ground water flows perpendicular to rivers. However, ground water flow near rivers is often dominated by underflow (ground water flow parallel to the river) (Larkin and Sharp 1992). In perched settings ground water flow near rivers may be minimal. Information on the nature of ground water flow paths near Coastal Plain rivers and the hydraulic properties of surficial aquifer, floodplain, and active channel sediments can improve water management decisions. This knowledge is critical to predicting the fate and transport of contaminants from spills and leaking underground tanks that occur near Coastal Plain Rivers. River-ground water interaction studies have utilized piezometers, ground water flow models, seepage runs, and inferences made from water temperature, water chemistry and isotopic composition data. Studies show that channel sediment hydraulic properties are very heterogeneous (Jones and Mullholland 2002). Numerous piezometers are required to adequately characterize hydraulic properties of an active river channel. Piezometer installation and monitoring in active river channels is difficult and expensive. Practical techniques are needed to characterize the geological framework of the active river channel that controls the river's relationship with the ground water system. In this study, we aim to use ground penetrating radar (GPR) as a tool to characterize active channel sediments underlying the Tar River and compare GPR transects with measured hydraulic conductivity and ground water input data. The goal is to determine if GPR can help to characterize the spatial variability of stream-ground water interactions. These techniques may be applied to a wide range of coastal plain rivers.

date/time interval

  • March 2005 - February 2006