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Estimate of aquifer properties by numerically simulating ground-water/surface-water interactions, Fort Wainwright, Alaska

Water-Resources Investigations Report 98-4088

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Abstract

MODFLOW, a finite-difference model of ground-water flow, was used to simulate the flow of water between the aquifer and the Chena River at Fort Wainwright, Alaska. The model was calibrated by comparing simulated ground-water hydrographs to those recorded in wells during periods of fluctuating river levels. The best fit between simulated and observed hydrographs occurred for the following: 20 feet per day for vertical hydraulic conductivity, 400 feet per day for horizontal hydraulic conductivity, 1:20 for anisotropy (vertical to horizontal hydraulic conductivity), and 350 per feet for riverbed conductance. These values include a 30 percent adjustment for geometry effects. The estimated values for hydraulic conductivities of the alluvium are based on assumed values of 0.25 for specific yield and 0.000001 per foot for specific storage of the alluvium; the values assumed for bedrock are 0.1 foot per day horizontal hydraulic conductivity, 0.005 foot per day vertical hydraulic conductivity, and 0.0000001 per foot for specific storage. The resulting diffusivity for the alluvial aquifer is 1,600 feet per day. The estimated values of these hydraulic properties are nearly proportional to the assumed value of specific yield. These values were not found to be sensitive to the assumed values for bedrock. The hydrologic parameters estimated using the cross-sectional model are only valid when taken in context with the other values (both estimated and assumed) used in this study. The model simulates horizontal and vertical flow directions near the river during periods of varying river stage. This information is useful for interpreting bank-storage effects, including the flow of contaminants in the aquifer near the river.

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Estimate of aquifer properties by numerically simulating ground-water/surface-water interactions, Fort Wainwright, Alaska
Series title:
Water-Resources Investigations Report
Series number:
98-4088
Edition:
-
Year Published:
1998
Language:
ENGLISH
Publisher:
U.S. Geological Survey ; Branch of Information Services [distributor],
Description:
iv, 35 p. :ill., maps ;28 cm.