Citation
| Mills, P.C., Bryson, J.R., Rose, C.E., and Coupe, R.H., 2007, Potential for infiltration through the fine-grained surficial deposits of the Bogue Phalia Watershed, Mississippi, 37. |
Abstract
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The U.S. Geological Survey is conducting a preliminary assessment of the potential for deep infiltration of water and ground-water recharge through fine-grained Mississippi embayment deposits. Findings of this study will provide insight into the potential for transport of agricultural chemicals to ground water in this and similar humid regions of the United States. During an annular period that began in March 2006, various sediment-physical-property, sediment-hydraulic, ground-water, stream-flow, and meteorologic data will be collected at two sites in the Bogue Phalia River watershed. The paired sites allow study of the somewhat varying sediment compositions distributed across the watershed. Relatively sandy soils planted with cotton compose the northern site near Gunnison; relatively sand-free soils planted with soybeans compose the southern site near Leland. Both sites are within 0.1 mile of the Bogue Phalia River. Within the study area, about 13 feet of predominantly silt sediments overlie at least 100 feet of sand deposits. The course sediments compose the Mississippi embayment alluvial aquifer, with ground-water levels generally about 15-30 feet below land surface. Instrumentation includes vertically nested piezometers and soil-moisture sensors, as well as a meteorologic station, deep ground-water well, and streamgage. Much of the instrumentation is monitored continuously with data-logging devices and the data served to the World Wide Web.
Preliminary data from the growing season of March-September 2006 indicate infiltration generally is limited to the uppermost 3-4 feet of the soil horizon, or just below the primary root zone of the planted crops. Following rainfall events, no appreciable increase in soil-moisture content was detected at monitored depths approaching 9 feet. Underlying ground-water levels and stream stage responded almost instantaneously to these events, indicating that the aquifer and nearby river are in direct hydraulic connection with ground-water levels affected by stream stage. The fine composition of the surficial sediments (generally containing less than 25 percent fine sand) and their presumably low vertical hydraulic conductivity appear to inhibit the deep infiltration of water. Presently, available data are not adequate to differentiate between the deep-infiltration characteristics of the varying sediment compositions that distinguish the two study sties. Additionally, the reported growing season was unusually dry, with 25 to 50 percent of normal seasonal rainfall (about 18 inches recorded). Infiltration response during a seasonally wet period, when evapotranspiration rates are correspondingly low, will need to be monitored to more fully assess the potential for deep infiltration through these fine-grained sediments. |
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