Henry Hagg Lake
- Washington County)
(From Atlas of Oregon Lakes, Johnson et al. 1985). Henry Hagg Lake is a large multipurpose reservoir, created in 1974 by the Bureau of Reclamation with the construction of an earthfill dam on Scoggins Creek in western Washington County. The reservoir was named in honor of Henry Hagg, a prominent Oregon dairyman and Washington County official who died in 1971. Scoggins Dam and Henry Hagg Lake form the primary component of the Bureau of Reclamation's Tualatin Project, which also includes the Patton Valley Pumping Plant, the spring Hill Pumping Plant, 20 booster pumping plants, and 86 miles of piped lateral distribution system.
To early settlers in the Tualatin Valley, the site of the modern project was known as "Twality Plains." It was one of the earliest farming settlements in Oregon. Agriculture developed quickly because there were numerous open areas that permitted cultivation without the expense and labor of clearing timber stands, and also because of the fertile soils in the Tualatin Valley. As the population increased, timbered tracts were cleared and more land came under cultivation. Hay, grain, and livestock production were the basis for the early agricultural economy and are still important in the economy of the area. From a small start, irrigation increased substantially and it soon became apparent that storage of water would be needed. Also, flood and drainage problems had been a source of concern since early settlement. Studies by the Bureau of Reclamation and Corps of Engineers made it clear that irrigation and flood control were not the only water resource needs in the area. There was a greater need for municipal and industrial water than originally anticipated. Construction of the long considered project was finally authorized in 1966. Construction of facilities began in 1972 and they were completed in 1978. Scoggins Dam, a 151-foot high earthfill structure was completed in 1974 and the reservoir filled in 1975. Total capacity of Henry Hagg Lake at full pool is 59,910 acre-feet, according to Bureau of Reclamation data.
Benefits from the project have been several. Agricultural land has been more productive by providing a dependable water supply through the growing season, especially during the late summer period. The top 20,300 acre-feet of reservoir space is used for flood control, sufficient to completely regulate a flood the size which occurs about once in 50 years at the damsite. Another 14,000 acre-feet of water are used for supplemental municipal and industrial purposes for four communities. In addition, 16,900 acre-feet of water are made available to improve the water quality of the Tualatin River by scheduled releases of water in the summer when natural flows are low.
Henry Hagg Lake has also become a very important recreational resource for people in the northern Willamette Valley. Boat launching and mooring facilities have been constructed and there are large day-use areas provided with picnic tables, shelters, and water and sanitary facilities. Water-skiing is a popular activity at the lake; but the south end of the lake has a 10 mph speed limit for the benefit of sailors, swimmers, and other users. The lake is stocked annually with rainbow trout and has rapidly become one of the state's more popular fishing lakes. A fish trap was built below Scoggins Dam to collect, for hatchery use, the anadromous fish blocked by the dam. Several dead trees were left in the reservoir to attract osprey, and portions of the reservoir area are managed to provide winter range for elk and black-tailed deer.
The drainage basin contributing to Henry Hagg Lake is a 37.5 square mile area in the foothills of the Coast Range. Saddle Mountain, 3535 feet above sea level, is the highest point in the drainage basin, indeed the highest point in the northern Oregon Coast Range. Geologically the area is underlain by a mixture of sandstone and older volcanic rocks that typify the foothills of the Coast Range. Thick soils of weathered clay and silt overlie the bedrock. A second-growth Douglas fir forest covers most of the drainage basin, with some open grassland used for grazing; there are also some small farms. Land ownership in the basin is, in part, private and, in part, federal (administered by the Bureau of Land Management). The shoreline of the reservoir was originally owned by the federal government (Bureau of Reclamation), although ownership has reverted to Washington County.
At full pool Henry Hagg Lake covers 1153 acres; it has a maximum depth of 110 feet, an average depth of 51 feet, and the water level fluctuates about 22 feet annually. It has, in general, maintained good water quality since filling in 1975. However, some problems have developed in recent years. Because of its recent origin, the banks of the reservoir are not yet stabilized and erosion and slumping produce local turbidity, particularly when waves are generated on the water surface by wind or motorboats. A pronounced thermal stratification develops in the lake in summer, with a sharp thermocline at about 30 feet (10 meters) depth. There is some tendency for oxygen depletion in the deeper water, below 30 feet. In recent years, unwanted rough fish species in the lake have increased in numbers, and they compete with trout for food and space. Plans have been made by the Oregon Department of Fish and Wildlife to chemically poison the lake to eliminate the unwanted species; however, this effort has been postponed until 1984 because of funding cuts.
Concentrations of major ions in the lake are comparable to those in other Willamette Valley reservoirs which are influenced by turbidity, such as Fern Ridge Lake and Hills Creek Lake, and somewhat higher than in most other lakes and reservoirs. At times there are large flocks of ducks and other water birds on the lake and around the shoreline. The phytoplankton occurring in the summer (McHugh, personal communication) are predominantly mesotrophic to eutrophic diatoms (Asterionella formosa, Synedra ulna), with occasional blue-green algal blooms occurring at a few localities in the reservoir. Blooms of Volvox globator (a green alga) have also been observed and may be common to new reservoirs as it has also been observed in newly created Lost Creek Lake near Medford. Concentrations of phosphorus and chlorophyl, the water transparency, and the partial depletion of dissolved oxygen in the hypolimnion all indicate the lake is highly mesotrophic. It is one of the more productive lakes in the Willamette Valley. It is common for new impoundments to be more eutrophic in the first few years after flooding while the easily available nutrients in vegetation and in the upper soil layers are entering the lake. The lake may shift to a lower trophic state as it stabilizes with time.