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The Basins

Precipitation map of Oregon showing the Willamette and Deschutes Basins.

This precipitation map of Oregon illustrates the contrasting climate regimes for the Willamette and the Deschutes Basins. Most of the Deschutes Basin receives less than 20 inches of precipitation annually while most of the Willamette Basin receives more than 60 inches annually. Precipitation data is from the PRISM model created by the Spatial Climate Analysis Service (SCAS) at Oregon State University.

The Pacific Northwest Hydrologic Observatory (PNW HO) will focus on the Willamette and Deschutes watersheds. These two basins have remarkably similar size (approx 28,000 square-kilometers) and share a common watershed divide along the crest of the Cascade Mountains; the Cascades also provide most of the water for the two drainages. There are other similarities: the geologies of both basins are primarily volcanic, with lesser areas in sedimentary rocks; most precipitation falls in the winter in both basins, with hot, dry summers; both basins drain into the Columbia River and share similar communities of anadromous and resident fish, some of which are threatened and endangered species; and both basins have a rich history of scientific research and public involvement in watershed issues. Despite these similaries, however, these basins have markedly different streamflow patterns, climatic gradients, geomorphologies, ecosystems, and water management issues.

The differences between the Deschutes and the Willamette begin with their contrasting precipitation regimes. Nearly all of the Deschutes basin receives less than 20 inches of precipitation a year while most of the Willamette receives more than 60 inches a year. The high precipitation levels in the Willamette create a flashy, surface-water dominated hydrologic system. The basin has a high drainage density and rapid runoff response. In contrast, in the Deschutes, groundwater is the dominant source of streamflow. Highly permeable, lava flows in the southwestern portion of the basin give rise to a laterally extensive groundwater system, which supports a stable discharge regime. Low temperature springs fed by the deep groundwater system provide ideal habitat for coldwater fish species, such as bull trout, that could otherwise not survive in an arid landscape.

About the Willamette River Basin

(excerpts from Draft Willamette Subbasin Plan, Northwest Power and Conservation Council, May 2004)

The Willamette Subbasin is home to 70 percent of Oregon’s population. Its main geographic features include Oregon’s largest river, the Willamette; the Coast Range, which borders the subbasin on the west; and the Cascade Range on the east. The 4,000-square-mile Willamette Valley has some of the richest farmland in the nation and produces about half of Oregon’s yearly farm sales.

One of the strengths of Willamette and Deschutes Basins as a hydrologic observatory site is the wealth of existing natural resources information. Both basin's have recently been the subject of major books.

Link to the Willamette Planning Atlas on the publishers website.

The Willamette River Basin Planning Atlas: Trajectories of Environmental and Ecological Change is a monograph that depicts past, present, and possible future scenarios for the Willamette River Basin. Many of the maps and datasets in the planning atlas can be viewed and downloaded from the Willamette Explorer website.

Link to A Peculiar River on the publishers website.

A Peculiar River: Geology, Geomorphology, and Hydrology of the Deschutes River, Oregon compiles major research papers that describe causes and consequences of the unique flow regime of the Deschutes Basin.

The Willamette Subbasin runs north to south between the Cascade Mountains on the east and the Coast Range on the west. It is bounded to the south by the Calapooia Range of the Cascade Mountains. The basin’s northern boundary is the mouth of the Willamette, at approximately Mile 86 of the Columbia River.

The Willamette River Subbasin is approximately 180 miles long and 100 miles wide. With an area of 11,478 square miles (7.3 million acres), the Willamette Basin occupies nearly 12 percent of the state of Oregon. (U.S. Army Corps of Engineers, 2000; Pacific NorthwestEcosystem Research Consortium, 2002). The Willamette River has a mainstem channel length of185 miles. A tributary to the Columbia River, the Willamette is Oregon’s largest river wholly contained within state boundaries. In addition, it is the nation’s 13th largest river by volume, with more runoff per square mile of drainage than any other large river in the coterminous United States (Kammerer, 1990).

The Willamette Basin lies within the Cascadia geologic province, which extends from British Columbia to Northern California. The western boundary of the province is about 70 miles off the Pacific Coast where the Juan de Fuca tectonic plate slides beneath the North America plate. Over millions of years, as the Juan de Fuca oceanic plate has collided with the western edge of the North American continent, the Coast Range has been lifted, forming the western boundary of the basin. …The eastern boundary of the Willamette Basin is defined by the volcanic crest of the Cascade Range (Pacific Northwest Ecosystem ResearchConsortium, 2002; Atlas of Oregon, 2001; Thieman, 2000)

A variety of rock types are present in the Willamette Basin. The Coast Range consists predominantly of marine sedimentary rock such as sandstone, siltstone, and mudstone. The slopes and foothills of the Coast Range make up about 20 percent of the basin area. The Cascade Range consists of numerous lava flows and volcanic sediments. The slopes and foothills of the Cascade Range account for more than 50 percent of the basin area (Oregon Department of Environmental Quality, 2004; Lee and Risley, 2002)…

The climate of the Willamette Basin is heavily influenced by the barrier effects of the Cascade Range and the rain shadow of the Coast Range. During the late fall and winter months, warm, wet maritime air masses from the southwest are forced up by the Coast and Cascade ranges, causing the moisture in the air masses to cools and condense as frequent and heavy rain in the lower elevations an snow in the upper elevations. Seventy-five percent of the annual precipitation in the Willamette Basin occurs from October through March. Precipitation at the crests of the Cascades and Coast Range can be as high 200 inches per year but declines sharply with elevation. The Willamette Valley floor receives only between 40 to 45 inches of precipitation annually.

Due in large part to the influence of the Coast Range and Cascades, 60 percent of the subbasin is forested. Agricultural land makes up 27 percent of the basin and is located mainly in the Willamette Valley. About a third of the agricultural land is irrigated (Wentz et al., 1998). Urban areas account for 5 percent of the basin (Oregon Watershed Enhancement Board, 2003).

Biologists estimate that there are 18 species of native amphibians, 15reptiles, 154 birds, 69 mammals, and 31 native fish currently breeding in the basin (Pacific Northwest Ecosystem Research Consortium, 2002). These species make their homes in widely diverse areas across the Willamette landscape.

About 2.5 million people, or 70 percent of Oregon’s population, live in the WillametteBasin. The Portland metropolitan area has 1.2 million people and is the state’s largest urban area. The three largest population centers of Portland, Salem, and Eugene-Springfield are situated along the banks of the Willamette River and the Interstate 5 corridor. Population growth in the basin is expected to double to nearly 4.0 million by 2050 (Willamette Restoration Initiative,2001). In the Portland metropolitan region, a 37 percent increase is expected between 2000 and2020 (Metro, 2003)….

Approximately 36 percent of the basin is in federal ownership. Mostof the federal land is located in the higher elevations of the Cascade and Coast ranges and is managed by the U.S. Forest Service (USFS) and U.S. Bureau of Land Management (BLM). More than 60 percent of the basin area outside urban growth boundaries—and more than 90 percent of the valley floor—is privately owned (Pacific Northwest Ecosystem ResearchConsortium, 2002).

About the Deschutes River Basin

(excerpts from the Draft Deschutes Subbasin Plan, Northwest Power and Conservation Council, May 2004)

The Deschutes Subbasin stretches over 10,700 square miles of land in central Oregon. Covering 11 percent of Oregon’s land area, the Deschutes River subbasin is larger than other Oregon watersheds, except the Willamette. The subbasin extends west to the crest of the Cascade Mountains, south to lava plateaus, east into the Ochoco Mountains and to the plateau between the Deschutes and John Day Rivers, and north to its confluence with the Columbia River. Its length reaches 170 air miles from peaks in the Cascade Mountains to where it joins the Columbia River, 205 miles from the Pacific Ocean. In width, it extends up to 125 miles from the eastern slopes of the Cascades to the western slopes of the Ochoco Mountains, and over the high desert landscape that covers much of the subbasin’s interior. … Larger population centers in the subbasin include Bend, Redmond, Madras and Prineville.

The landscape of the Deschutes Subbasin ~ it’s volcanoes, cinder cones, lava flows, sandy soils, spring-fed streams, and deep canyons ~ speaks of the turbulent natural events that shaped the subbasin. The sedimentary, igneous and metamorphic rocks that define its shape range from more than 250 million years old to as young as 1,300 years old (O’Connor et al. 2003)....To the west and south, the Cascade Range, an active volcanic arc, molds the high, rugged subbasin rim. Volcanic activity along the crest and volcanic centers along the eastern flanks create a topography of young volcanoes and lava flows. These porous volcanic soils and lava formations absorb most snow and rain that falls on the Cascade Basin and create the large underground aquifer that give the Deschutes and several tributaries naturally stable flows throughout the year. …
The eastern rim of the watershed displays some of the Deschutes subbasin’s oldest geological roots. These Mesozoic (250 to 65 million years old) and Paleozoic (more than 250 million years old) rocks lay within the headwaters of the Crooked River and Trout Creek drainages. Deposits from the John Day Formation cover most of the Crooked River watershed, including much of the Ochoco and Mutton Mountains. …

The Columbia River Basalt Group underlies much of the northern, central and eastern parts of the Deschutes watershed (O’Connor et al. 2003). This basalt group, which creates many of the major ridges in the subbasin, is between 1,000 and 2,000 feet thick. …

While the headwaters of the Deschutes River and most major tributaries receive large amounts of precipitation, much of the subbasin lies in the rain shadow of the Cascade Mountains and is sheltered from western Oregon’s heavy rainfall. Average annual precipitation amounts to more than 100 inches on the eastern slopes of the Cascades, mostly as snow, but drops to only 40 inches in the Ochoco Mountains and 10 inches at lower central locations. ...

In a natural state, the Deschutes River displays a unique flow regime that sets it apart from other eastern Oregon rivers. The U.S. Reclamation Service recognized the river’s unique character in 1914 and reported “The flow of the river is one of the most uniform of all streams in the United States, not only from month to month, but also from year to year.” Historic flows in the Deschutes River were especially uniform in the reach between Benham Falls (RM 180.9) and the mouth of the Crooked River (RM 113.7) (USGS 1914).

The steady flows through the length of the Deschutes River were primarily due to the volcanic geology of the upper subbasin and substantial groundwater storage. Porous volcanic soils and lava formations absorb much of the snow and rain that falls on the Cascade Basin, creating a large underground aquifer. Most of this groundwater discharges into streams in three areas: the southern part of the subbasin in and near the margin of the Cascade Range, the Metolius Basin adjacent to the Cascade Range, and the area surrounding the confluence of the Deschutes, Metolius and Crooked rivers extending downstream to about Pelton Dam (Gannett et al. 2001)….

The geology and climate of the Deschutes Subbasin create a diverse landscape of mountain forests, juniper and sage rangelands, rugged outcroppings and deep river canyons. Wetlands and riparian areas account for only a small portion of the subbasin’s total acreage. Higher elevations in the subbasin display ponderosa and lodgepole pine forests, wet meadows and savannah-like mountain grasslands. Peaks range from above 11,000 feet in elevation in the Cascades to about 6,500 feet in the Ochoco Mountains. …Along the upper river corridor, stands of old growth ponderosa pine and lodgepole are often mixed with lush wet marshes in the summer and large expanses of dry meadows.…

The Deschutes basin contains an estimated 6,850,700 acres, consisting of 6,797,300 acres of land and 53,400 acres of permanent water (NRCS 1997). The federal government owns about 50 percent of the subbasin, or about 3,380,900 acres. ….

Lands of the Warm Springs Tribal Reservation extend over approximately 641,000 acres, or about 7 percent of the subbasin. Tribal lands lie mostly in the lower Deschutes River subbasin. …Lands in private ownership comprise about 42 percent of the land area in the subbasin. Most of these lands support agricultural, forest and range uses.

The Deschutes Subbasin has long been a home to humans. American Indian groups ~ including ancestors to the Warm Springs and Wasco tribes ~ inhabited areas along the Columbia River and Cascade Mountains for at least 13,000 years before Europeans arrived. Evidence from Newberry Crater at the subbasin’s south end indicates that humans inhabited that region at least 10,000 years ago, as did mastodons, camels and other now extinct species (USFS 1996). …

The upper and middle Deschutes watershed is currently experiencing tremendous growth, and this trend is expected to continue. The growth rate in Deschutes County, particularly around the cities of Bend and Redmond, has been significantly higher than in most other rural areas. The county continues a 20-year trend of leading the state with the highest population growth. U.S. Census Bureau information indicates that the population of Deschutes County grew 53.9 percent between 1990 and 2000 (Hough 2002). This steady growth has continued for more than 30 years, with the county’s population more than doubling in size between 1970 and 1990….The explosive growth in Deschutes County is also higher than most places in the United States. It was marked as the 74th fastest growing county in the nation between 2001 and 2002….

The influx of new residents has changed the character of some communities and rural areas. While agriculture, wood products, manufacturing, recreation and tourism continue to be primary land uses in the subbasin, some lands are being converted for new uses. Small agricultural towns and irrigation districts ~ particularly those around Bend ~ now have large residential development and hobby farms. There is also more demand for recreational areas, which has led to the development of at least seventeen 18-hole golf courses and/or destination resorts in Deschutes County alone. …
… The need for summer irrigation water prompted the construction of irrigation storage reservoirs in the White River drainage, beginning in 1928, to supplement the natural stream flow. …Today, irrigation water is supplied by three large reservoirs in the upper Deschutes subbasin and two large reservoirs in the Crooked River drainage. Water management operations have replaced the stable natural flows in the upper Deschutes River with very low flows during the winter when the reservoirs are being filled, and very high flows during the summer irrigation season, when water is being released from the reservoirs. Below Bend, where most of the water is diverted to meet irrigation needs, summer flows in the middle Deschutes River drop to about 60 cfs.

Irrigation withdrawals affect anadromous salmonids in several ways. Low summer flows and high water temperatures in diverted stream reaches limit habitat for rearing juveniles. They also restrict fish passage to other areas and connectivity between fish populations. ….

Dams were also constructed on Deschutes Subbasin streams to generate power. Early hydroelectric dams include the Cline Falls Power Company and Cove Power Plant, which were operating by 1901 and 1910, respectively. These early dams did not provide fish passage.

Construction of the largest dam complex in the Deschutes Subbasin began in the late 1950s. The Pelton Round Butte Complex, built on the Deschutes River near RM 100, had a significant effect on fish production in the basin. The complex was constructed with fish passage facilities, but attempts to pass juvenile anadromous fish through the project failed. Consequently, the dam complex blocked anadromous fish from part of their historic spawning and rearing habitat, particularly in the Squaw Creek, Metolius River and Crooked River systems. ...

While natural flows in the mainstem are fairly stable, those in tributaries are often more variable. Annual, and sometimes daily, stream flows are particularly changeable in eastside tributaries draining semiarid lands in the Cascade rain shadow that do not receive abundant groundwater discharges. Stream flows in westside tributaries, that drain the wetter, cooler slopes of the Cascades and benefit from groundwater and surface water are generally less variable….


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