By Roger Edwards
Bull Run Lake is described in the Atlas of Oregon Lakes as a well-protected, oligotrophic lake that is the source of Portland’s drinking water. It is a 466 acre, linear lake about 1.5 miles long and 0.5 miles wide on a NW to SE axis. Its perimeter is 4.2 miles and it sets in a 3.5 square mile drainage basin that receives >110" annual precipitation. Mean depth is 20 m. and maximum depth is about 70 m.
Public access to the lake has been restricted since June 17, 1892 when President Benjamin Harrison established the Bull Run Reserve and proclaimed that entry or settlement there was not allowed. Portland residents first took delivery of water from the Bull Run watershed on January 2, 1895. President Theodore Roosevelt signed the Bull Run Trespass Act on April 28, 1904, which further limited entry to government agents and water company employees, "in the discharge of their duties", and specifically forbade the grazing of "stock of any kind" within the Reserve.
Releases from the lake to augment water supply were common from 1958 to 1962. With the completion of the downstream Bull Run Reservoir 2 in 1962, no releases were needed until 1985, when water demand or low rainfall again made them annual events through 1992. Water was pumped down to a level 30’ below full pool in 1992,. Since then, there have only been releases in 1999 and 2000.
The formation of the lake has never been absolutely established. It is in a cirque basin, 9 miles west of Mt. Hood. Valleys between the lake basin and Mt. Hood serve as the headwaters for the Sandy and Hood Rivers. Forested slopes of 30-60% surround the lake on three sides. Unconsolidated materials lying on top of volcanic flows of basaltic andesite form the natural dam (Figure 1). The unconsolidated materials have been ascribed to both a glacial or landslide origin. In either case, the material is porous enough that there is no overland flow coming from the lake. The outlet channel extends about a quarter mile from the lake, where it pools, and the water disappears. There is seldom any water in the channel unless it is being intentionally released. The Bull Run River forms from a series of springs lower in the valley from the lake. A USGS study of the lake’s hydrology includes a diagram of its setting, and shows the upper and lower flumes that capture the water from springs between the lake and the river. Only during times of high flow is there a continuous overland stream between the upper and lower flumes. There is ample evidence that high porosity and instability of the steep slopes around the lake is characteristic of much of the basin. A trip around the lake’s perimeter shows that most of the stream inputs to the lake appear as oozes or just wet spots below the high water line, rather than running water. Often, running water can be heard but not seen, as streams disappear into the jumble of rocks deposited at the edge of the lake.
In October 1992, the USGS set up a stage recorder on Bull Run Lake (station 1413860). Daily values for the last day of each month from then to September 2001 were averaged and are presented in Table 1. Typically, the lowest stage level occurs in October and then rises to peak in May. The raw data from the complete set shows a range of levels from 3144.0 in October 1992 to 3184.9 in February 1996. There are many Spring readings >3178, the overflow elevation of the dike. When the water level gets above the overflow elevation, it flows across the dike and pools along its outer side.
USFS (1979). Bull Run Planning Unit, Final Environmental Statement. USDA-FS-FES(Adm)-76-16.
Short, Casey (1983) Water, Portland’s Precious Heritage. City of Portland.
Johnson, D.; R. Petersen; R. Lycan; J. Sweet; M. Neuhaus; & A. Schaedel (1985). Atlas of Oregon Lakes. Oregon State University Press.
Snyder, Daniel & Dorie Brownell (1996). Hydrogeologic Setting and Preliminary Estimates of Hydrologic Components for Bull Run Lake and the Bull Run Lake Drainage Basin, Multnomah and Clackamas Counties, Oregon. USGS Water Resources Investigations Report 96-4064.
Portland Water Bureau (1994-2001) Unpublished monitoring data from Bull Run Lake.