USE OF HEAT TO DETERMINE THE EXCHANGE BETWEEN THE MISSISSIPPI RIVER AND THE MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER IN NORTHWESTERN MISSISSIPPI, OCTOBER 2007-SEPTEMBER 2008

The Mississippi River Valley Alluvial Aquifer (MRVA) in northwestern Mississippi is in direct connection with the Mississippi River, discharging into the River at times of base flow and being recharged by the Mississippi River at times of high flow. Modeling studies have indicated that over the long term, there is a net zero exchange of water between the Mississippi River and the MRVA. However, because of increased groundwater withdrawals for agriculture over the past few decades, groundwater levels have been declining in the MRVA; this decline has likely changed the interaction between the Mississippi River and the MRVA. Changes in surface- and groundwater interactions are important to understand, especially as local agencies attempt to implement policies to use the MRVA in a sustainable manner. In order to quantify the exchange between the Mississippi River and the alluvial aquifer, continuous data collected over the last decade from wells located near the Mississippi River were used to identify recharge and discharge periods and to estimate the net balance between the river and aquifer. Historical water-level data were also used to determine if the relation has changed over time.