Feasibility of farm-scale infiltration galleries for managed aquifer recharge in an agricultural alluvial aquifer of Northeast Arkansas

Abstract

Agriculture-heavy alluvial aquifer regions around the world have experienced severe groundwater declines due to irrigation demand. This consequence has been observed in the United States in the latter half of the 20th century, notably in the Central Valley of California and in the Mississippi River Valley. In some portions of the Mississippi River Valley, such as the Cache River Critical Groundwater Area (CRCGA) of northeast Arkansas, drawdown has exceeded 30 m and portends aquifer depletion in the near future. In addition to adopting surface-water storage and irrigation efficiency methods, farm-scale managed aquifer recharge (MAR) with infiltration galleries (IG), gravel-filled trenches designed to move surface water into the aquifer, may be a useful tool for reducing declines. Low-permeability surface deposits, which limit and create significant variation in natural recharge across the region, also control the placement of MAR systems. It is therefore critical to understand the variability of surface deposits, as well as underlying aquifer properties, to best plan the placement, design, and operation of such systems. This study aimed to characterize surface and upper aquifer conditions to assess the feasibility of IG in the central CRCGA. Available well logs were used to interpolate the approximate thickness of surface deposits and identify thinner areas. Approximately 37% of the study area has less than 5 m of confining material at the surface and included 28 existing reservoirs that could act as recharge water sources. Guided by this mapping effort, geophysical and sediment surveys were conducted at selected sites. The upper unsaturated alluvial aquifer of fine silty-sand had estimated hydraulic conductivities of 0.20–2.79 m d−1. These results are promising for the implementation of farm-scale IG in the study region and suggest that small MAR systems could be a useful tool for groundwater management in other agricultural aquifer systems given the proper placement.