Surficial Geology and Soils in the Mississippi Delta: In Search of Infiltration Data

Author(s): Mason, P.; Thompson, D.

The water-bearing sands and gravels of the Mississippi River Valley alluvial aquifer (MRVA) underlying Mississippi's Delta region are very prolific and are important to agricultural interests. Significantly, the aquifer's overlying capping layer, or topstratum, is important in understanding the sustainability of this resource. This relatively thin topstratum is a primary controlling factor in determining how much direct recharge from precipitation passes from the surface to the aquifer. This process ultimately plays an important role in recharging this increasingly stressed and heavily utilized aquifer. Concepts and historical research vary regarding the permeability and character of the topstratum. Fisk (1944) described the topstratum as "various combinations of sand, silts, and clays" comprising a "relatively impervious topstratum". Little is known about specific locations in the Delta where direct recharge through the topstratum might be enhanced, restricted, or absent. As a result, previous efforts to simulate the groundwater flow system have postulated various schemes for assigning infiltration. These have included: 1) one uniform infiltration rate, 2) low rates in most areas with moderately low rates in zones controlled by topstratum geology, and 3) moderate to high rates in well-drained soils zones with no infiltration elsewhere. In an effort to clarify and illuminate the level of knowledge regarding this capping interval, systematic research and review of existing literature, surface geological mapping, soils mapping, and pertinent data sets is being undertaken. Some of the available data may be reprocessed or enhanced in order to better identify the various soil parameters, geomorphologic features, and depositional units which are thought to be useful tools in predicting and developing infiltration rates for the MRVA.

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