--> Architecture of Alluvial Aquifers and the Correlation Between Depositional Patterns and Hydraulic Conductivity Trends: An Example from the Quaternary of Mississippi, by M. J. Neton, S. C. Young, J. Dorsch, D. A. Summers, and C. D. Olson; #90986 (1994).

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Abstract: Architecture of Alluvial Aquifers and the Correlation Between Depositional Patterns and Hydraulic Conductivity Trends: An Example from the Quaternary of Mississippi

Michael J. Neton, Steven C. Young, Joachim Dorsch, David A. Summers, Christopher D. Olson

Aquifers deposited in alluvial environments are typically highly heterogeneous, with hydraulic conductivity (K) values commonly ranging over 7 orders of magnitude. High permeability alluvial deposits include sieve- and sheetflood-deposited gravel of alluvial fans, longitudinal-bar gravel of braided rivers, and channel- and point-bar sand and gravel of meandering rivers. The arrangement and interconnection among high and low permeability deposits produces preferred groundwater flow pathways. Successful groundwater modeling requires identification of these flow pathways, adjacent flow barriers and lower permeability zones. Limited resources prevent exhaustive field tests to detail the hydraulic conductivity field. Prudent site characterization requires co-development and integration of depositional facies model and hydraulic tests. A depositional model aids in well placement and design, construction of plausible aquifer architectures and provides a framework for designing and interpreting hydraulic and tracer tests. Data collected from the sedimentologic literature, coupled with data from a 25-hectare site in Mississippi, illustrate the correlation between hydraulic conductivity trends and sedimentologic features. Field data obtained from the 25-hectare site includes gravel-pit facies mapping, sediment coring, 7 large-scale (>12 hours) aquifer tests, numerous single-well and electromagnetic borehole (EMB) flowmeter surveys, a large-scale (>250m) natural gradient test, and 7 recirculating tracer tests at different scales.

Data from air photos and these tests indicate a strongly sinuous, abandoned meander is a major flow pathway and a control on groundwater flow in the area. Groundwater flow and contaminant-transport modeling, based on hydraulic conductivity values from pump test and EMB flowmeter data, verifies refraction of flow lines into, and preferred flow through, the high K meander-fill deposits.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994