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.

This legal protection and the physical difficulty of access, has limited visits to the lake. Up until the 1960’s, a trip to the lake still required packing in on a 16 mile trail from the dam forming Bull Run Reservoir 1. A log cabin at the lake provided overnight shelter for work crews. These crews built a 10’ timber and rock fill dam across the natural outlet in 1915 to raise the full pool level of the lake to an elevation of 3178’. A 500’ long dike was constructed in the years 1917-21 to isolate a shallow area on the NW side of the lake where lake seepage was thought to be excessive. Further efforts to reduce seepage were mounted during1919-25, when rock and soil were applied to areas on the lake side of the dike. By 1961, new areas of high permeability had been identified and sealed with bentonite clay. In this same timeframe, the outlet dam was reconstructed with gates at 3147 and 3158’ elevation.

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.

In 1994, the Water Bureau began more vigorous monitoring of the lake in response to concern that lake releases were altering the natural water temperature of the receiving stream. By taking temperature profiles of the lake, and measuring same day temperatures at the upper and lower spring flumes, the lake level that best matched the temperature of the receiving stream was determined. Concrete pier blocks were then placed in the lake out to this level and an intake conduit was fixed to the piers so that future releases would have minimal temperature shock on downstream aquatic life.

The Bureau profiles were taken at four week intervals as long as access to the lake was not blocked by snow. There has been no trouble getting to the lake from June through October, but May, November, and December are always questionable. The lake does freeze over in the Winter, although to what degree is not certain. Warming is well under way by the time the roads are cleared in the Spring. Below about 25 m., the water temperature is always 4†C. There is a strong stratification that develops above this level in the Summer. By sorting the temperature profiles by the seasonal temperature at 1 m depth, the 3-D graph shown in Figure 2 was produced to characterize the summer stratification. The Figure shows the lake is homothermal in Winter, and stratifies in early Summer. The thermocline grows in depth through the Summer and then drops to a lower depth in the Fall as surface temperatures cool. Calculating the mean of the 1 m temperatures in the month that they were measured provides a look at the seasonal variation in Table 1. The range of temperatures in the full data set goes from a low of 4.8 in December of 1997 to a high of 20.4 in July of 1994. There have only been two December profiles and it is possible that because there was access to the lake in those years, the temperatures measured were warmer than they would be when lake access was blocked.

The monitoring that the Water Bureau has performed at the lake has made it possible to characterize its status with the Oregon Lake Condition Index. This Index is under development by the Center for Lakes and Reservoirs at Portland State University. It is a standardized survey of key lake features, which permits a systematic comparison of different lakes. The Index report for Bull Run Lake is presented in Table 2. Its score of 10/none/1/2000 ranks it as an excellent example of an oligotrophic lake, with no known threats of degradation. It lacks data on just one of the key lake features, and the survey was completed with data collected in the year 2000.

References:

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.