Hydrogeologic framework of the Willamette Lowland aquifer system, Oregon and Washington

Abstract

The RASA Program represents a systematic effort to study a number of the Nation's most important aquifer systems, which, in aggregate, underlie much of the country and which represent an important component of the Nation's total water supply. In general, the boundaries of these studies are identified by the hydrologic extent of each system and, accordingly, transcend the political subdivisions to which investigations have often arbitrarily been limited in the past. The broad objective for each study is to assemble geologic, hydrologic, and geochemical information, to analyze and develop an understanding of the system, and to develop predictive capabilities that will contribute to the effective management of the system. The use of computer simulation is an important element of the RASA studies to develop an understanding of the natural, undisturbed hydrologic system and the changes brought about in it by human activities and to provide a means of predicting the regional effects of future pumping or other stresses.The final interpretive results of the RASA Program are presented in a series of U.S. Geological Survey Professional Papers that describe the geology, hydrology, and geochemistry of each regional aquifer system. Each study within the RASA Program is assigned a single Professional Paper number beginning with Professional Paper 1400.

Location and timing of river-aquifer exchanges in six tributaries to the Columbia River in the Pacific Northwest of the United States

“…The ground-water diverges from the west side of the river with a downward vertical gradient around the losing reach. Caldwell (1998), Donato (1998), Gannett et al (2001), Kjelstrom (1995), Konrad et al (2003), Lee and Risley (2002), and Woodward et al (1998).…”

“…Synoptic gains and losses, representing river-aquifer exchanges at a point in time were calculated from seepage runs made during a period of stable flow (typically 1 day to 1 week) along the Willamette River in August 1992, June 1993, and September 1993(Woodward et al, 1998; the Deschutes River in May 1992, May 1994, October 1995, and February 1996(Gannett et al, 2001; the Lemhi River in August and October 1997 (Donato, February 2002, and September 2002(Konrad et al, 2003. Temporal patterns of river-aquifer exchanges are based, in part, on repeated seepage runs conducted at different seasons in the Willamette, Deschutes, Lemhi, and Methow Rivers.…”

A mass Budget for Mercury in the Willamette River Basin, Oregon, USA

“…Material deposited during low flow in a given year had a good probability of being scoured out of the system during high flows in the same year, keeping the net sediment-water flux essentially at zero. Currently, flows in the Willamette River and its major tributaries are highly regulated by reservoirs, whose controlled releases minimize seasonal variation (e.g., annual average flow at Salem (RM 84) is now only 621 m 3 s −1 (23 000 cfs)) (Laenen and Risley, 1997;Woodward et al, 1998). Although the Main Stem can still produce flows in excess of 2830 m 3 s −1 (100 000 cfs) during 100-or 500-year flood events (as in 1964(as in and 1996(as in (OCS, 2004), low flows are more common and very high flow (scouring) events less frequent.…”

“…The Basin's drainage system is dominated by the northward-flowing Willamette River and its 13 major tributaries (Figure 1). Its headwaters arise in two forks, the Coast and the Middle, which flow northward to form the Main Stem near Eugene, which then flows north for approximately 187 river miles (RM) to its confluence with the Columbia River (Laenen and Risley, 1997;Woodward et al, 1998). Oregon's three largest urban areas, the cities of Portland, Salem, and Eugene, border the Main Stem (Altman et al, 1997).…”

Precipitation Impacts on Groundwater Levels in the Ephemeral Holgate Lake: A MODFLOW Inquiry

“…Average annual precipitation over the area is 48.7 inches (USGS StreamStats). Evapotranspiration is estimated to range from 15 to 16 inches per year in the aquifer system (Woodward et al 1998). …”