Previous and Ongoing Projects

The U.S. Geological Survey has numerous recently completed or ongoing hydrologic investigations in the Willamette Basin. These include: 1) a recently completed descriptive analysis of regional ground-water flow conducted under the USGS Regional Aquifer-Systems Analysis (RASA) program, 2) an ongoing study of the surface-water hydrology and quality of the Willamette River and its tributaries conducted in cooperation with the Oregon Department of Environmental Quality (DEQ), 3) an ongoing assessment of water quality conducted under the USGS National Water-Quality Assessment (NAWQA) program, and 4) a quantitative analysis of the ground-water flow system in the Portland Basin completed in 1990.

Each of these studies either covers some important aspect of the hydrology in the Willamette Basin or deals comprehensively with the hydrology in part of the basin. None of them deals with the basin-wide ground-water hydrology in a comprehensive and quantitative manner, although they provide a sound foundation for such a study.

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Willamette Basin RASA Study

The recently completed RASA study included an analysis of the geology of the regional ground-water system, identification of regional aquifers, and description of their characteristics. The study also included an estimate of the regional ground-water budget, a description of the regional ground-water flow system, and construction of two simple cross-sectional ground-water flow models. Work was largely restricted to the basin-filling sediments in the Willamette Valley; very little work was done with the Columbia River Basalt Group aquifers. This study was primarily done using existing data.

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USGS-DEQ Water Quality Studies

The surface water and water-quality study consists of two phases. Phase I, which is completed, consisted of 1) developing precipitation-runoff and streamflow models of the entire basin for future water-quality modeling, 2) collecting and analyzing suspended-sediment data to determine past and present sediment transport, and 3) reconnaissance sampling for trace element and organic contaminants. Phase II, which is ongoing, will 1) quantify major source areas of pesticides and trace elements in the basin, 2) quantify the depletion of dissolved oxygen associated with bed-sediment oxygen demand, and 3) identify processes controlling dissolved oxygen concentrations upstream from Salem. Dye tracer studies to determine river travel time and streamflow measurements to determine main-stem gains and losses from ground water were made in support of the hydrologic modeling. These studies identified a large seasonal variability of ground-water flow to the main-stem Willamette River and large exchange of water between the stream and streambed. More detailed studies will be conducted from June to September, 1995 as part of the ongoing NAWQA program.

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Willamette NAWQA Study

An assessment of water-quality in the Willamette Basin is ongoing under the USGS National Water-Quality Assessment (NAWQA) program. The long-term goal of the NAWQA program is to describe the status and trends in surface- and ground-water quality in the basin. Surface-water work to date has included extensive sampling and chemical analysis of streams, streambed sediment, and aquatic biological tissue throughout the basin; ecological and habitat characterization also have been completed. Ground water has been sampled from 70 shallow wells in the valley and analyzed for an extensive list of constituents. Ten wells were drilled and sampled in the Portland area to characterize the effects of urban land use on ground-water quality. Additional ground-water sampling and analysis have been done to investigate the interchange between ground water and surface water in alluvial deposits adjacent to the Willamette River.

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Portland Basin Ground-Water Study

The Portland Basin ground-water study, completed in 1990, covers the extreme northern part of the Willamette Valley. The study was done in cooperation with OWRD, the City of Portland, and Clark County, Washington and included the delineation of regional aquifer units and estimation of their hydraulic properties. A ground-water budget was developed that included an estimation of ground-water recharge, measurements of discharge to springs and streams, losses to evapotranspiration, and discharge to wells. Additionally, extensive water-level data were collected for all aquifer units. Using the above information, a three dimensional ground-water flow model was developed to simulate the ground-water system. Since completion of the original study, the model has been used extensively to study aquifer vulnerability and zones of contribution to wells in Clark County Washington.


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Last modified: Fri Mar 28 14:53:38 1997