Transcript Groundwater Hydrology of the Willamette Basin, Oregon Abstract 70% of the population in Oregon lives above the seven major aquifer systems in the.

Groundwater Hydrology of the Willamette Basin, Oregon
Abstract
70% of the population in Oregon lives above the seven major aquifer
systems in the Willamette Valley. The seven primary hydrostratigraphic
units include the High Cascade, Upper Sedimentary, Willamette Silt,
Middle Sedimentary, Lower Sedimentary, Columbia River Basalt, and the
Basement Confining.
Precipitation recharges these units at an average rate of 22 in/yr
between the high and lowland areas. The period of greatest rainfall occurs
from November to April and allows for more water to infiltrate than is
withdrawn from the regional aquifer systems. Summer months with
evaporation and irrigation account for the most water use. Regional
groundwater levels fluctuate by about 65 ft each year and are projected to
decline with time as population in the valley increases and recharge varies
with changing climate dynamics.
Prepared by: Brittnie Andrew
Western Oregon University Spring 2008
ES473 Environmental Geology
Rainfall Recharge
The Willamette Valley is a large scale watershed. Rainfall on the east
side of the Coast Range, the west side of the Cascades and within the valley
provide a system of recharge to the underlying water table. Rainfall is
greatest in winter months. In Salem the annual rainfall is 79 inches during
the months between December and March (Conlon et al. 2005). Figure 2
Figure 3 Shows the water system including precipitation for the year
2000 in the central portion of the basin. The amount of precipitation varies
from season to season so understanding the exact amount of rainfall
recharging the aquifers is difficult. Figure 4 shows the water cycle system
with the influencing factors of ground water, precipitation, and percolation.
Human Help
The current aquifer system is supplying the people within the valley
with plenty of the water needed to sustain life, and then some. Over time
based on the fluctuation of the groundwater levels more efforts are going to
need to be put into the task of conserving water. However if efforts where
made sooner conservation of water would be less costly in the future. Basic
and small actions can be taken to help prevent water lose within the system.
 Watering plants in the morning (also helps the plants).
 Washing the car in the lawn if needed.
 Collecting rainwater and storing it for future use.
Figure 3 Water use
and budget for
Central Willamette
Basin in 2000 (Colon
et al. 2005).
Figure 1 shows the
general location of the
Willamette value
within Oregon as well
as sub basins (OSU,
2008).
Figure 5 Cobble Mountain Watershed Reserve (Reed, 2008).
Overview of the Willamette Basin



The seven primary hydrostratigraphic units include the High Cascade,
Upper Sedimentary, Willamette Silt, Middle Sedimentary, Lower
Sedimentary, Columbia River Basalt, and the Basement Confining all
deposited within the basin (Figure 1).
Precipitation
Figure 4 A break
down of the
Hydrologic Cycle
(S.A. Water, 2008).
Conclusions
Percolation
The Willamette Basin is home to 1.9 million people, all in need of a
continuous water supply.
Rain fall is the primary source of recharge to the system.

Water use, and climate effect the overall amount of ground water.

The future of the basin, water budgeting.
Water Use
The Willamette Basin groundwater provides water to people, farming,
and industries by means of wells. In 2000 the total amount of water that was
pumped was about 300,000 acre-ft, of the total, 81 percent was pumped for
irrigation, 14 percent for public supply, and 5 percent for industrial use
(Colon et al., 2005). During the periods of little to no recharge, April
through September in 2000, Figure 2, much of the stored water is
consumed. Evaporation and transpiration are also factors in water use.
Transpiration, best described as “tree sweat” accounts for the use of 28in/yr
(Colon et al., 2005). This number as well varies from year to year, but that
is based on the depth of saturation and the height of the water table. The
water table levels fluctuate each year for varies reasons.
 The amount of water withdrawn is greater than the amount of water
imputed. More withdrawn during summer months then winter months.
 Warmer climate means higher evaporation rates.
Figure 2 Willamette River Portland Area (OSU, 2008).
 Building of more wells provides the potential for more water to be
used.
The Willamette Basin groundwater levels change over time based
on varies factors. Factors may increase the level, rainfall and or surface
water amounts, and factors may decrease the level, excessive
withdrawal. Precipitation provided the most impute into the
groundwater system, as seen in Figure 3, this occurs during the winter
months. Humans play an important role in the use and recharge of
water, and our impact has the potential to be negative if steps are not
taken soon to reduce water wasting.
References Cited
• Conlon, Terrence D, et al. Ground-Water Hydrology of the Willamette Basin,
Oregon Scientific Investigations Report 2005–5168 (2005). 83 pages
• Oregon State University, 2004 Willamette Basin Explorer. Dept. home page.
June 2004 May 27, 2008 <http://willametteexplorer.info/index.aspx>.
• Reed, Christopher W. “Town of Longmeadow 2006 Water Quality Report.”
Longmeadow Water Department. 15 Apr. 2008. 27 May 2008
<http://www.longmeadow.org/dpw/consumerconfidence.htm>.
• S.A. Water. The Water Cycle. 8 Feb. 2008. 26 May 2008
<http://www.sawater.com.au/SAWater>.
• Woodward, Dennis G, Marshall W Gannett, and John J Vaccaro. Hydrogeologic
Framework of the Willamette Lowland Aquifer System (1998).