| South Fork Bull Run River | |
| Name Etymology: | Possibly after cattle that escaped and ran wild along the river between 1849 and 1855[1] |
| Map: | Bull run river oregon watershed map.png |
| Map Size: | 300 |
| Pushpin Map: | USA Oregon |
| Pushpin Map Size: | 300 |
| Pushpin Map Caption: | Location of the mouth of the South Fork Bull Run River in Oregon |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Oregon |
| Subdivision Type4: | County |
| Subdivision Name4: | Clackamas County |
| Length: | 6miles[2] |
| Discharge1 Location: | 0.6miles from the mouth |
| Discharge1 Min: | 5.4cuft/s |
| Discharge1 Avg: | 111cuft/s |
| Discharge1 Max: | 3630cuft/s |
| Source1: | Mount Hood National Forest |
| Source1 Location: | Township Meadow, Clackamas County, Oregon |
| Source1 Coordinates: | 45.4339°N -121.9889°W[3] |
| Source1 Elevation: | 3260feet[4] |
| Mouth: | Bull Run River |
| Mouth Location: | Bull Run Reservoir 2, Clackamas County, Oregon |
| Mouth Coordinates: | 45.4522°N -122.1225°W |
| Mouth Elevation: | 863feet |
| Basin Size: | 15.4sqmi |
The South Fork Bull Run River is a tributary, about 6miles long, of the Bull Run River in the U.S. state of Oregon. Part of the system that provides drinking water to the city of Portland, it flows generally west through a protected part of the Mount Hood National Forest in Clackamas County. It joins the Bull Run River at Bull Run Reservoir 2, about 8miles from the larger stream's confluence with the Sandy River.
The river, which begins in Township Meadow in the Mount Hood National Forest, flows northwest and then west through Clackamas County and the Mount Hood National Forest. It receives its only named tributary, Cedar Creek, from the right before reaching a United States Geological Survey (USGS) stream gauge 0.6miles from the mouth. The South Fork joins the main stem Bull Run River at the larger stream's river mile (RM) 8 or river kilometer (RK) 13, near the midpoint of Bull Run Reservoir 2.[5]
Since 1974, the USGS has monitored the flow of the South Fork Bull Run River at a stream gauge 0.6miles from the mouth. The average flow between then and 2008 was 111cuft/s. This is from a drainage area of 15.4sqmi. The maximum flow recorded during this period was 3630cuft/s on February 7, 1996. The minimum was 5.4cuft/s on October 13, 1994.[6]
The Bull Run River watershed, which includes the South Fork Bull Run River, drains 139mi2.[7] The basin, which is the main source of Portland's drinking water, is largely restricted to uses related to water collection, storage, treatment, and forest management. The South Fork Bull Run River basin of about 15.4mi2 amounts to about 11 percent of the total Bull Run River watershed,[6] which is managed by the Portland Water Bureau and the United States Forest Service.[8]