Introduction and Background

Key Elements

• This report presents the results of a study that is part of the Nature Conservancy Sustainable Rivers Project begun in 2002 in partnership with U.S. Army Corps of Engineers.
• The study objective was the creation of an environmental flow framework for the McKenzie River basin, Oregon, necessary to sustain aquatic and terrestrial ecosystems.
• The goal of this report is to provide a hydrologic, geomorphic, and ecological baseline assessment for basin stakeholders.
• The McKenzie River is approximately 90 mi in length and has a drainage area of approximately 1,300 mi².
• The study area was divided into three basins with 12 reaches extending from Trail Bridge Dam to the Willamette River confluence. The upper McKenzie River basin (Reaches 1 and 2) extends from Trail Bridge Dam to the South Fork McKenzie River confluence. The middle McKenzie River basin (Reaches 3 through 8), including the South Fork McKenzie River downstream of Cougar Dam, extends from the South Fork McKenzie River confluence to Leaburg, Oregon. The lower McKenzie River basin (Reaches 9 through 12) extends from Leaburg to the Willamette River confluence.
• Streamflows in the upper basin are fed by highly productive springs. The middle basin is situated in the rugged and highly dissected Western Cascades, where the hydrology is controlled by less-permeable geology, snowmelt, and rain-on-snow events. In the lower basin, downstream of Leaburg, the river flows through a generally unconstrained floodplain to its confluence with the Willamette River.
• The McKenzie River is regulated by the Carmen-Smith–Trail Bridge hydropower dam complex, Cougar and Blue River flood control dams, and the Leaburg and Walterville hydropower canals.

Purpose of the Study

The McKenzie River environmental flow study is a collaborative effort of The Nature Conservancy (TNC), the Eugene Water & Electric Board (EWEB), The U.S. Army Corps of Engineers (USACE), and the U.S. Geological Survey (USGS) to develop environmental flow requirements for the McKenzie River basin. In 2002, TNC and the USACE formed the Sustainable Rivers Project (SRP), a partnership aimed at developing, implementing, and refining environmental flow requirements downstream of dams. Environmental flows can be defined as the streamflow needed to sustain ecosystems while continuing to meet human needs. Developing environmental flow requirements typically involves a collective process of interested and involved stakeholders to identify and prioritize streamflow objectives. The process often is a series of steps and feedback loops that include defining the streamflow requirements, implementing them into the dam operations, monitoring and modeling the streamflow changes and their effect on the river ecosystem, and then adjusting and refining the streamflow requirements if necessary. In addition to dams, other anthropogenic factors in a watershed contribute to freshwater ecosystem degradation, such as water diversions, channel revetment, timber harvest, wetland draining, invasive species, gravel extraction, and other factors, which are taken into consideration during the process (Tharme, 2003; Acreman and Dunbar, 2004; Richter and others, 2006; The Nature Conservancy (2009e).

Since the creation of the partnership, SRP projects have been implemented on a number of rivers around the Nation, including the Bill Williams River in Arizona (Shafroth and Beauchamp, 2006), the Savannah River between South Carolina and Georgia (The Nature Conservancy, 2009a), the Big Cypress Bayou in Texas, the White and Black Rivers in Arkansas, the Green River in Kentucky (The Nature Conservancy, 2009b), the Roanoke River in Virginia (The Nature Conservancy, 2009c), and the Willamette River (The Nature Conservancy, 2009d). Within the Willamette River basin, environmental flow guidelines have already been developed for the Coast and Middle Fork Willamette River basins (Gregory and others, 2007a, 2007b). Recommendations for new dam flow releases and ecological monitoring were made by Coast and Middle Fork Willamette River basin stakeholders who attended a workshop in January 2007. This McKenzie River basin environmental flow study is the second phase of the Willamette River Sustainable River Project. Eventually other Willamette River subbasins, such as the Santiam, also will undergo an environmental flow development process.

Study Goals and Tasks

The goal of this study was the creation of an environmental flow framework for the McKenzie River basin that is based on a scientific assemblage of ecological, hydrologic, and geomorphologic baseline data. The assemblage will include an assessment of changes resulting from anthropogenic effects that have occurred in the basin. Tasks to achieve this goal include:

1. Conducting reconnaissance level hydrologic, geomorphic, and ecological assessments along the mainstem, and some tributaries, of the McKenzie River.
2. Assembling and synthesizing information necessary to enable managers and stakeholders to develop environmental flow recommendations for the system.
3. Developing a future data monitoring plan to evaluate the environmental flow guidelines.

Purpose of this Report

This report will provide McKenzie River basin stakeholders with a compilation of relevant streamflow, geomorphic, and ecological data and analyses necessary for them to prescribe the rate, frequency, duration, and timing of flow releases from McKenzie River basin dams for various downstream locations.

Description of Study Area

The McKenzie River drains a 1,300 mi² area in western Oregon (fig. 1). From the headwaters at Clear Lake in the Cascade Range the river traverses approximately 90 mi before it joins the Willamette River near Eugene, Oregon. Elevations in the McKenzie River basin range from about 375 ft at the Willamette River confluence to 10,358 ft at the summit of South Sister. The river slope ranges from less than 0.2 percent in the wide, unconstrained floodplain in the Willamette Valley to greater than 1.2 percent upstream of Belknap Springs, Oregon, at river mile (RM) 75 (fig. 2). The upstream reaches of the McKenzie River, 24 percent of the basin, are fed by springs and snow melt in the High Cascades, a high elevation area underlain by young relatively permeable material consisting of High Cascade volcanic rocks and glacial deposits. The middle reaches flow through older volcanic material of the Western Cascades, a region of older less permeable weathered volcanic material representing 58 percent of the basin. Streams deeply dissect the Western Cascade area. In the lower reaches, the remaining 18 percent of the basin is Quaternary alluvium primarily along the valley bottoms (Sherrod and Smith, 2000) (fig. 3).

The climate of the McKenzie River basin is temperate marine characterized by dry summers and wet winters (fig. 4). About 90 percent of the normal precipitation falls between October and May. Mean annual precipitation ranges from about 40 in. in the Willamette Valley at Eugene to more than 125 in. at the crest of the Cascades. About 35 percent of the precipitation falls as snow at the 4,000-ft elevation, and more than 75 percent at the 7,000-ft elevation.

Major tributaries in the upper McKenzie River basin include the Smith River, Horse Creek, the South Fork McKenzie River, and the Blue River. The terrain of the upper basin is mountainous, with steep ridges and narrow floodplains and terraces in the valleys along the streams. The hydrology is largely controlled by the basin geology. In the upper basin, precipitation infiltrates through porous volcanic High Cascades terrain and emerges from large spring complexes that support steady year-round discharge and cool stream temperatures in the mainstem McKenzie River. Additional discussion regarding the hydrogeology of Cascade volcanics and their relationship to McKenzie River basin spring-dominated streamflows and stream temperatures can be found in Stearns (1928), Ingrebritsen and others (1994), Manga (1997), Tague and Grant (2004), Jefferson and others (2006), and Tague and others (2007).

The middle and lower McKenzie River basin, downstream of the South Fork McKenzie River confluence (RM 60), is situated in the rugged and highly dissected Western Cascades, where the hydrology is controlled by geology, snowmelt, and rain-on-snow events. As a consequence of less-permeable geologic formations, streamflow in this region is more responsive to storm runoff than the upper basin, which results in high sediment yields (U.S. Forest Service, 1995; Stillwater Sciences, 2006b). Major tributaries include Quartz, Gate, and Martin Creeks and the Mohawk River. Between Blue River (RM 57) and the Leaburg Dam (RM 39), the channel is confined. Downstream of Leaburg, Oregon (RM 33), the river flows through a generally unconfined valley with a broad floodplain to its confluence with the Willamette River.

Differences in basin yield between the upper and lower basins of the McKenzie River basin are evident in the streamflow data (table 1). Basin yield, computed by dividing mean streamflow by drainage area, generally is highest in the upper basins, such as above Trail Bridge Dam, Lookout Creek, and Blue River. Yield generally is lowest in the downstream basins, such as Cedar Creek and the Mohawk River. Although the yield at the McKenzie River near Coburg streamflow-gaging station is slightly higher than at the McKenzie River near Vida station, the Coburg streamflow record (1945–72) represents a wetter period. The Vida streamflow record for the same time period has a computed yield of 4.72 (ft³/s)/mi².

The McKenzie River basin supports timber harvesting, recreation, agriculture, and manufacturing. Most of the human population in the basin is near or within the Eugene and Springfield urban growth boundaries. The floodplain in the lower McKenzie River basin is mostly privately owned and used for agriculture. Overall, the Federal Government owns approximately 70 percent of land in the basin. The Bureau of Land Management (BLM) owns tracts in the Mohawk River subbasin and the middle parts of the McKenzie River basin. Above Quartz Creek (RM 54) the McKenzie River basin is almost entirely within the Willamette National Forest (Northwest Power and Conservation Council, 2004).

Study Framework

The study area was divided into three basins with 12 river reaches, each having distinct streamflow, geomorphic, and sediment input conditions (fig. 5; table 2). The upper McKenzie River basin (Reaches 1 and 2) extends from Trail Bridge Dam to the South Fork McKenzie River confluence; the middle McKenzie River basin (Reaches 3–8), including the South Fork McKenzie River downstream of Cougar Dam, extends from the South Fork McKenzie River confluence to Leaburg, Oregon; and the lower McKenzie River basin (Reaches 9–12) extends from Leaburg, Oregon to the Willamette River confluence. Ten of the 12 reaches are on the mainstem of the McKenzie River. The two tributary reaches include the South Fork McKenzie River downstream of Cougar Dam (Reach 3) and the Blue River from the Blue River Dam to the McKenzie River confluence (Reach 5). Where the downstream end of a reach is near a major stream confluence, the downstream end of the reach is always defined as being located just upstream of the confluence. Streamflow from the confluent stream is included in the streamflow of the next downstream reach. This was done to minimize the difference in streamflow between both ends of the reach and to use a single representative reach discharge in the analyses. Two of the reaches (8 and 10) were between the diversion dam and return streamflow locations of the Walterville and Leaburg canals. Key study reaches that are emphasized in this report include Reach 1 (immediately downstream of Trail Bridge Dam), Reach 3 (immediately downstream of Cougar Dam), Reach 5 (immediately downstream of Blue River Dam), Reach 7 (includes a long-term streamflow-gaging station near Vida and is affected by the cumulative effects of upstream dams), and Reach 12 (affected by the cumulative effects of upstream dams and canal diversions).

Streamflow Regulation

Since the early 1900s, streamflow in the McKenzie River basin has been altered through the construction of dams and canals (fig. 6; table 3). EWEB owns and operates the Walterville and Leaburg canals, completed in 1910 and 1930, respectively, which are operated for hydropower production. With the exception of canal seepage losses and minor withdrawals, most of the diverted water returns to the McKenzie River. Under the current Federal Energy Regulatory Commission (FERC) license, EWEB diverts as much as 2,500 ft³/s for its Leaburg and 2,577 ft³/s for its Walterville power canals so long as a minimum of 1,000 ft³/s remains in the McKenzie River. However, EWEB provides a minimum flow in the river of 1,050 ft³/s. An additional 40 ft³/s is provided to the Leaburg fish hatchery. Streamflows at the USGS streamflow-gaging stations near Leaburg (14163150) and Walterville (14163900) are monitored in real time and used to control canal diversions.

In the early 1960s, EWEB constructed the Carmen-Smith River Hydroelectric Project. From the Carmen diversion reservoir, water is diverted through a tunnel into the adjacent Smith River subbasin (also within the McKenzie River basin) (fig. 6). The Smith River dam is used to provide a sufficient elevation drop for the production of electricity. Flow from the dam goes through a power tunnel to the Carmen powerhouse. Water passing through the Carmen powerhouse is discharged at the head of Trail Bridge Reservoir near the confluence of the Smith and McKenzie Rivers. Trail Bridge Dam is used for reregulating the outflow of the Carmen-Smith Hydroelectric Project to closely match the inflow at Carmen Diversion Dam.

In the 1960s, the USACE constructed the Cougar and Blue River Dams on the South Fork McKenzie and Blue Rivers, respectively. Having a combined useable storage of about 236,000 acre-ft, both dams are used for flood control, navigation (Willamette River), downstream irrigation, fisheries, water quality, and recreation (U.S. Army Corps of Engineers, 2009a, 2009b). Cougar Dam also is used for hydropower production.

Upstream of Vida, McKenzie River basin withdrawals for consumptive water use are minimal in relation to total streamflow because the upper basin is almost entirely managed by the U.S. Forest Service (USFS) and has limited agricultural and residential water demands. As a consequence, the upper basin dams (Cougar, Blue River, and Carmen-Smith–Trail Bridge) historically have not changed annual streamflow. Their effect has been more on the annual distribution of daily streamflows, which is discussed in the Hydrology section. Most water withdrawals in the McKenzie River basin occur in the lower basin (Reaches 9-12) between Leaburg and Eugene. The largest water users are EWEB (water intake at Hayden Bridge near Springfield), the Weyerhaeuser plant near Springfield, the Springfield Utility Board, and the Leaburg fish hatchery. Other water withdrawals in the basin, mostly through groundwater pumping, are for agriculture and residential use.

Previous McKenzie River Basin Studies

In recent years, numerous research papers and reports have been published specific to hydrologic, ecological, and biological issues in the McKenzie and Willamette River basins. Stearns (1928), Ingrebritsen and others (1994), Manga (1997), Tague and Grant (2004), Jefferson and others (2006), and Tague and others (2007) discussed the geologic framework of the High Cascades in the upper McKenzie River basin and its relationship to spring-dominated streamflow. For more than 50 years, research on forest hydrologic, geomorphic, and ecological dynamics has been based on field data collected in the H.J. Andrews Experimental Forest, which is a Long-Term Ecological Research (LTER) site in the Lookout Creek basin (in the Blue River basin) (H.J. Andrews Experimental Forest, 2009).

In the 1990s, the USFS, BLM, and Weyerhaeuser produced a series of watershed analyses for various streams in the basin. Many of these studies were related to timber harvesting and its effects on fisheries and ecological habitat. These analyses included the lower and middle reaches of the McKenzie River (Bureau of Land Management, 1998a, 1998b), the upper McKenzie River basin (U.S. Forest Service, 1995), Blue River (U.S. Forest Service, 1996), Horse Creek (U.S. Forest Service, 1997), South Fork McKenzie River (U.S. Forest Service, 1994), Quartz Creek (Ecosystems Northwest, 1998), and the south and north sides of the lower McKenzie River basin (Weyerhaeuser, 1994, 1995).

A series of publications has resulted from the Federal Energy Regulatory Commission (FERC) relicensing applications for the EWEB projects (Eugene Water and Electric Board, 2008a, 2008b; Karl Morgenstern, Eugene Water and Electric Board, oral commun., 2009). The Walterville and Leaburg hydroelectric projects were relicensed by FERC in 1997, and those licenses will not expire until 2037. An outcome of the relicensing was implementing minimum streamflows of 1,000 ft³/s in the reaches of the McKenzie River where EWEB diverts as much as 2,500 ft³/s for its Leaburg power canal and 2,577 ft³/s for its Walterville power canal. The Carmen-Smith Hydroelectric Project Final License Application was submitted to FERC in November 2006 and a Settlement Agreement with 16 signatories was submitted in October 2008 (Stillwater Sciences, 2006a, 2006b; Eugene Water and Electric Board, 2008b). Because the Cougar and Blue River Dams are owned by a Federal agency (USACE) and not a power utility, they are not regulated under the FERC relicensing process.

Bull trout (Salvelinus confluentus) throughout the Klamath and Columbia River basins was listed as threatened by the U.S. Fish and Wildlife Service (USFWS) in 1998. In early 1999, the National Marine Fisheries Service (NMFS) listed spring Chinook salmon (Oncorhynchus tshawytscha) in the McKenzie River basin and other upper Willamette River basins as threatened. As a result of these listings, Endangered Species Act (ESA) consultations began between the Federal agencies whose operations were affecting the listed species (known as “Action Agencies”) and the NMFS and USFWS (known as the “Services”). During an ESA consultation, the Action Agencies are required to create Biological Assessments (BA), which are submitted to the Services. The BA also includes a proposed recovery plan that outlines how the Action Agency will reduce its effect on the critical habitat of the listed species. In the Willamette ESA consultation, the Action Agencies include the USACE, Bonneville Power Administration, and Bureau of Reclamation. The USACE submitted its first BA in 2000 and a supplemental BA in 2007 for the Willamette River basin that included specific recovery plans for the McKenzie River basin (U.S. Army Corps of Engineers, 2000, 2007). In July 2008, NMFS released their decision on the BA plans through a Willamette Project Biological Opinion (National Marine Fisheries Service, 2008a, 2008b). NMFS decided that the BA plans were insufficient for mitigating the effect of the water projects on critical habitat. The Biological Opinion ordered additional measures, which included improved fish passage, temperature control, and changes in downstream streamflows. Included in the Biological Opinion are flow release targets for Cougar and Blue River dams for different seasonal life histories for the ESA-listed fish (table 4).

As a result of the Willamette River ESA listings and consultation, a coordinated effort by various Willamette River basin stakeholders to improve critical habitat was made under the auspices of the Willamette Restorative Initiative. The group submitted the Willamette Subbasin Plan, which included proposals to modify streamflow releases from dams in the Willamette River basin (Northwest Power and Conservation Council, 2004).

Aside from the ESA consultations, ecosystem habitat issues in the McKenzie River basin also are driven by stream temperature. Before the construction of the selective withdrawal tower at Cougar Dam, Hansen (1988) modeled the effects of the dam operations on downstream water temperatures. More recently Rounds (2007) modeled water temperatures downstream of Cougar Dam using observed dam streamflow releases made with the selective withdrawal tower (completed in 2005) in operation. The Oregon Department of Environmental Quality (ODEQ), as required under the Federal Clean Water Act, has developed stream-temperature Total Maximum Daily Load (TMDL) allocations for many streams in Oregon. In 2006, ODEQ finalized a TMDL plan for the Willamette River basin. Some stream reaches within the McKenzie River basin were listed as having exceeded their temperature TMDL as a result of dam streamflow releases, canal streamflow diversions, and limited riparian shade (Oregon Department of Environmental Quality, 2006).

First posted February 8, 2010