Bull Run River (Oregon)
The Bull Run River is a tributary of the Sandy River in the U.S. state of Oregon. Beginning at the lower end of Bull Run Lake in the Cascade Range, it flows generally west through the Bull Run Watershed Management Unit, a restricted area meant to protect the river and its tributaries from contamination. The river, impounded by two artificial storage reservoirs as well as the lake, is the primary source of drinking water for the city of Portland, Oregon.
It is likely that Native Americans living along the Columbia River as early as 10,000 years ago visited the Bull Run watershed in search of food. Within the past few thousand years they created trails over the Cascade Range and around Mount Hood, near the upper part of the Bull Run watershed. By the mid-19th century, pioneers used these trails to cross the mountains from east to west to reach the fertile Willamette Valley. In the 1890s, the City of Portland, searching for sources of clean drinking water, chose the Bull Run River. Dam-building, road construction, and legal action to protect the watershed began shortly thereafter, and Bull Run water began to flow through a large pipe to the city in 1895.
Erosion-resistant basalt underlies much of the watershed, and streams passing over it are relatively free of sediments. However, turbidity increases when unstable soils sandwiched between layers of basalt and other volcanic rocks are disturbed and wash into the river during rainstorms. Despite legal protections, about 22 percent of the protected zone was logged during the second half of the 20th century, and erosion increased. For a time in 1996, Portland had to shut down the Bull Run supply because of turbidity and switch to water from wells. A law passed later that year prohibited most logging in or near the watershed, and since then the Portland Water Bureau and the United States Forest Service have closed many of the logging roads and removed culverts and other infrastructure contributing to erosion.
Mature trees, most of them more than 500 years old and more than in diameter, cover about half of the watershed, and the rest of the watershed is also heavily forested. Annual precipitation ranges from near the water supply intake to as much as near the headwaters. More than 250 wildlife species, including the protected northern spotted owl, inhabit this forest. Downstream of the BRWMU, the watershed is far less restricted. In the late 19th century, an unincorporated community, Bull Run, became established near the river in conjunction with a hydroelectric project and a related railroad line. About of the lower river is open to fishing and boating, and the land at the confluence of the Bull Run and Sandy rivers has been a public park since the early 20th century.
Course
The Bull Run River begins at Bull Run Lake, a natural body of water modified slightly by the Portland Water Bureau, near Hiyo Mountain in the Mount Hood Wilderness. Originating in Clackamas County north of Forest Road 18, its unnamed headwater tributaries enter the lake. Flowing northwest from the lake, the river immediately enters Multnomah County and continues generally northwest for about. Along this stretch, the river flows by a United States Geological Survey stream gauge at river mile 20.9 or river kilometer 30.6, passes under Forest Road 1025 and Forest Road 10 and receives Blazed Alder Creek from the left and Log Creek and Falls Creek, both from the right. Then the river turns southwest and passes another stream gauge just before entering Bull Run River Reservoir 1 at RM 15. Also entering the reservoir are Fir Creek from the left, North Fork Bull Run River from the right, then Deer, Cougar, and Bear creeks, all from the right. The Bull Run River exits the reservoir via a spillway from the river mouth. Forest Road 10 runs roughly parallel to the right bank of the river from near the headwaters to Southwest Bull Run Road, near the mouth.Entering Bull Run River Reservoir 2, the river receives Camp Creek from the left, re-enters Clackamas County, and receives South Fork Bull Run River from the left. The river exits the reservoir via a spillway at about RM 6. Below Reservoir 2, Forest Road 10 is on the river's right bank, and Forest Road 14 is on the left. The river flows by a stream gauge at RM 4.7 and passes under Forest Road 14 before receiving the Little Sandy River from the left at about RM 2. The river then turns northwest, passes under an unnamed road and then under Southeast Bull Run Road near the unincorporated community of Bull Run, which is on the river's right, and the defunct powerhouse of the Bull Run Hydroelectric Project, which is on the left. Southeast Camp Namanu Road runs roughly parallel to the river along its right bank from here to the mouth. Along this stretch, the river receives Laughing Water Creek from the right and enters the Sandy River at Dodge Park, about from the larger river's confluence with the Columbia River.
Discharge
The USGS and the water bureau operate a stream gauge at RM 4.7, which is downstream from Bull Run Reservoir 2 and the water system intake. Measurements are for the river only and do not include water diverted upstream of the gauge to the city water supply or to a former power plant. The maximum flow at this station was on December 22, 1964, and the minimum flow was on October 4, 1974. The drainage area above this gauge is, about 77 percent of the whole watershed. The maximum flow occurred during the floods of December 1964 and January 1965, rated by the National Weather Service as one of Oregon's top 10 weather events of the 20th century.Since 1966, the USGS has monitored the flow of the Bull Run River at a stream gauge from the mouth. The average flow between then and 2008 was. This is from a drainage area of, about 34 percent of the entire watershed. The maximum flow recorded during this period was on November 5, 1999. The minimum was on October 28–31, 1987.
The uppermost stream gauge on the main stem is at RM 20.9, downstream from the outlet structure at Bull Run Lake. In operation since 1992, the gauge recorded an average flow of between then and 2009. This was from a drainage area of, about 4 percent of the total watershed. The maximum flow recorded during this period was on February 7, 1996. The minimum was on October 28, 1992.
In addition to the three main-stem gauges, the USGS operates five other stream gauges in the Bull Run watershed. Each of the following tributaries has one gauge: Fir Creek, Blazed Alder Creek, the North Fork, the South Fork, and the Little Sandy.
Near the outlet structure of Bull Run Lake, a USGS water-stage recorder at RM 21.9 has collected data on lake levels since 1992. The maximum lake content between then and 2009 was on February 9, 1996, and the minimum was on October 29, 1992. The two Bull Run reservoirs are also equipped with water-stage recorders.
Geology
, 10 to 20 million years old, that underlie much of the Bull Run watershed are exposed near the bottoms of steep canyons along the river and its tributaries. In the western half of the watershed, the Rhododendron formation, rich in sediments, overlies the basalt, and later volcanic flows of basalt and andesite overlie both older formations. Areas of thick talus occur in the eastern part of the watershed at elevations higher than above sea level, and north-facing slopes above show evidence of glaciation. Over many centuries, streams in the watershed have carved canyons through the Rhododendron formation to the level of the basalt. Since basalt resists erosion, water traveling over it remains relatively free of sediments. Less than 2 percent of the watershed is at high risk for landslides.The Bull Run River's three reservoirs—Bull Run Lake, Bull Run Reservoir 1, and Bull Run Reservoir 2—are oligotrophic and do not sustain many life forms. Bull Run Lake is in a steep-sided cirque blocked at its lower end by a series of lava flows topped by debris from a glacial moraine. Small streams flow into the lake from ridges above it, and water exits the lake mainly by seeping through porous rock to enter the Bull Run River about downstream. Evidence suggests that over the past several thousand years, although forest fires in the area and volcanic activity on Mount Hood or Mount St. Helens have caused temporary changes in the lake's limnological condition, it "has always returned to conditions similar to those seen at present." Turbidity is sometimes a problem in Reservoirs 1 and 2 when unstable soils sandwiched between layers of lava erode into tributaries, especially the North and South forks.