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Geohydrology and numerical model analysis of ground-water flow in the Pullman-Moscow area, Washington and Idaho

Water-Resources Investigations Report 89-4103

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Abstract

The geohydrology of the Pullman, Washington-Moscow, Idaho area was investigated by mapping geohydrologic units, determining the distribution of hydraulic head in each unit, and determining some of the components of the water budget. This information was used to construct a three- dimensional groundwater-flow model that incorporates three layers--a surficial loess layer, a Wanapum Basalt layer, and a Grande Ronde Basalt layer. The model was used to assess the effects of changes in the rate of withdrawal of groundwater on the water levels in the geohydrologic units and on streamflow in the area. Recharge to the groundwater system was calculated independent of the model. It was determined that current farming practices use soil moisture more effectively than did natural vegetation, and these practices have reduced groundwater recharge by nearly 10%. The three-dimensional model was calibrated using the time- averaged method for the period 1974-85, and was evaluated by simulating historical pumpage rate changes (1890-1985) and comparing calculated with observed water-level changes. Model results indicate that groundwater levels would stop declining if pumpage were stabilized at a constant level. Levels will continue to decline into the foreseeable future, however, as long as groundwater pumpage continues to increase. The source of the additional simulated pumpage is streamflow depletion near pumping locations. (USGS)

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Geohydrology and numerical model analysis of ground-water flow in the Pullman-Moscow area, Washington and Idaho
Series title:
Water-Resources Investigations Report
Series number:
89-4103
Edition:
-
Year Published:
1990
Language:
ENGLISH
Publisher:
U.S. Geological Survey ; Books and Open-File Reports Section [distributor],
Description:
vi, 73 p. :ill. ;28 cm.