My watershed is relatively small in comparison to Oregon’s Willamette River or Columbia River watersheds. However, that doesn’t exclude the Tualatin River Basin from human influences that alter natural hydrological rhythms.
Within the 712 square miles (455,680 acres) drained by the Tualatin Basin: 20% of the watershed’s area is inhabited by 500,000 people in densely populated urban areas; 30% is farm or vineyard lands; and 50% is forest land.
The demand for water in the Tualatin Basin is primarily for: irrigation, drinking water, industrial use, recreation, fish/wildlife habitat, and a small hydroelectric generating power-house.
The major human-made structures in the watershed that alter flow include:
– two dams
– irrigation pumping stations
Oswego Lake Dam
The dam holds back water diverted from Tualatin River to form Oswego Lake (or Lake Oswego). The water fills an old channel of the Tualatin River that was scoured and filled by the Bretz or Missoula Floods 15,000 to 13,000 years ago. In 1871, wooden dams were built on Oswego Creek to raise the water level of the lake, but since these never lasted very long, a concrete dam was constructed in 1921.
The dam caused Tualatin River overflow to back up during 1996 winter floods, resulting in millions of dollars in property damage. A recently completed spillway project at the east end of Lakewood Bay is designed to allow faster drainage of sudden spates. (Cut from: Oregon Hikers.org )
Oswego Lake is a private water body whose primary water right is hydropower generation. Secondary uses include irrigation, aesthetic viewing, contact recreation, fishing, and boating.
Hydropower generated here is sold to Portland General Electric Company. Public Law 97-345, signed in U.S. Congress in 1982, exempts this hydroelectric facility from the Federal Power Act. I don’t know what this means. However, the powerhouse is very small…
Human Influence on Environmental Flow/ Natural Hydrological Rhythms –
Although the environmental flow of the lake system seems to be well-managed with the newer spillway installation, it is my impression that biodiversity is stressed in this particular arm of the Tualatin River basin. Natural features have been highly modified by: logging in the late 1800’s, saw mill and steel foundry industrial use in the early 1900’s, and present-day affluent residential development. Native flora is greatly replaced by formal lawns, and ornamental plantings. Riparian areas have been replaced by shoreline development that includes seawalls, docks, and boathouses. Water quality is threatened by silt caused by erosion, nutrients from lawn fertilizer, and improperly functioning septic systems adjacent to the lake and tributary streams. The current Lake Oswego Comprehensive Plan recognizes these issues. It includes recommended action measures to address water quality and restoration/preservation of natural features.
Scoggins Dam/ Henry Haag Lake on Tualatin River tributaries: Scoggins, Sain, and Tanner Creeks
Scoggins Dam is an earthfill dam constructed during 1972–75 to store water during the winter for summer and fall use. Three tributaries flow into Hagg Lake—Sain, Scoggins and Tanner Creeks. Scoggins Dam is owned by the Bureau of Reclamation and managed by the Tualatin Valley Irrigation District. Stored water from Hagg Lake is used for irrigation, municipal and industrial use, and flow augmentation in the Tualatin Basin to support water quality and protect fish and wildlife.
Scoggins Dam stores 53,640 acre-feet of water in Henry Hagg Lake as active storage—the amount of water that can be moved in or out of the reservoir between the intake structure and the top of the spillway gates. Another 7,000 acre-feet of stored water that is not engineered to be removed exists below the intake structure. It is for the protection of fish if the lake were to be drafted down completely to the intake structure.
Scoggins Dam is authorized by the U.S. Congress to provide flood control for communities located down- stream. The dam controls runoff from a 39 square mile watershed (about 5% of the Tualatin Basin). From November to April, 20,000 acre-feet are designated for flood control storage. The dam does not generate electricity. During the summer months, recreation is a major activity at Hagg Lake and the surrounding area. (Cut from source: Tualatin River Flow Management Technical Committee, 2013 Annual Report)
Pumping Plants and Distribution Systems
Two downstream pumping plants receive water released at Scoggins Dam for distribution into irrigation systems. One, the Patton Valley Pumping Plant, is constructed on the bank of Scoggins Creek about 2.5 miles downstream from the dam. About 3.5 miles of buried, gravity-fed pipeline serve approximately 1,900 acres of land. The other, Spring Hill Pumping Plant, is located on the bank of the Tualatin River about 9 miles downstream from the dam. About 80 miles of deliver water pumped by nine irrigation pumps to about 10,300 acres.
Human Influence on Environmental Flow/ Natural Hydrological Rhythms –
Flow management is carefully monitored in the Tualatin River watershed basin. Key stake-holders work together to assure that Tualatin River seasonal and annual flows and levels meet human needs and, at the same time, address biodiversity needs. Water management entities partner with local eco-related agencies to encourage public involvement with riparian-related projects and education opportunities.
This week’s UNLESS challenge helped me to identify one of the eco-related agencies in my community that I can contact to learn about partnering to promote wetland awareness interpretive studies in the section of the Tualatin River basin where I live,and to investigate the possibility of monitoring flow data for the tributary in our section of the watershed.
This week’s UNLESS… Earth-friendly challenge: Taking the Pulse of your Watershed River’s Heartbeat
Great post, Jane.
There is a whole lot more water in that system than the fresh water portion of our local river (creek would be more appropriate, even though it is fed by several smaller creeks :)). It is certainly not pumped anywhere! When there is enough, it just flows over the tiny weir and on into the harbour. – Ken
With talk about impending drought conditions in this area, I wonder how the pumping ability of the basin will be impacted.
It was very interesting to learn about the weir in your river’s flow system. We both have engineering at work in how our local water finds its way 😉
This has been a good conversation, Ken!
… and I am inspired to explore, camera at the ready, Jane. I just can’t promise how soon that will be. 🙂
But, isn’t that the thrill of exploring with photography? Camera ready? You are all set 🙂