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.
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.
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.
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.
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