This study deals with the upper Strawberry Creek watershed which lies east of Oxford Street in Berkeley (Figure 2). This area includes all lands owned by the University of California that may influence the water quality of Strawberry Creek. The entire runoff from the 1163 acre (1.8 mi2) watershed is delivered to the entrance of the city culvert at Oxford Street which runs underground in a westerly direction, eventually emptying into San Francisco Bay near University Avenue.
Strawberry Creek has two main branches, the North and South Forks. The South Fork is a fourth order stream, whereas the North Fork is a third order tributary. The confluence of the two forks is located in the Eucalyptus Grove at the western edge of the central campus about 400 feet east of Oxford Street. On the central campus alone there is approximately 6270 linear feet of streamcourse. Stormwater routing and stream channel culverting has greatly altered the natural drainageways in both the North and South Fork subwatersheds.
The South Fork subwatershed comprises 759 acres (1.2 mi2). It is bounded by the Panoramic-Sugar Loaf ridge on the south, Frowning Ridge (Grizzly Peak) on the east and the North Fork subwatershed to the north. Hamilton Creek drains the southeastern portion of this watershed and joins Strawberry Creek below the Botanical Garden. Another unnamed branch drains the area from Grizzly Peak to the Animal Behavior Research Station and joins Strawberry Creek just above the retention dam.
An earthen retention dam is located at the entrance to the lower fire trail in the canyon. Its function is to protect the central campus and Haas Recreation Area from flood damage. The "Big Inch" bypass culvert begins at the dam and carries all upper canyon drainage underground to its outlet adjacent to the Faculty Club on the central campus. Chicken Creek and two other unnamed tributaries which drain the western portion of the Lawrence Berkeley Lab (LBL) complex and the central canyon area are routed directly into the Big Inch bypass culvert.
The original Strawberry Creek channel continues downstream of the retention dam and becomes the "Little Inch" bypass culvert when it enters a drop inlet located just above Haas Recreation Area The Little Inch culvert travels underneath the stadium and empties adjacent to the Women's Faculty Club. A small open channel then connects this culvert to the South Fork at the outlet of the Big Inch culvert next to the Faculty Club. Flow in the original creek channel below the retention dam is supplied solely by local runoff. A low flow bypass once diverted flow through the retention basin dam to the former creek channel, but the pipe inside the dam has collapsed. A subdrain which underlies the old creek bed from the retention dam to the drop inlet above Haas draws groundwater out of the channel during dry periods, resulting in this section of channel drying up most of the year.
The South Fork on the central campus is therefore made up of flow carried by the two bypass culverts from the canyon. This fork meanders through the southern side of the campus and eventually meets the North Fork in the Eucalyptus Grove to form the Main Branch of Strawberry Creek. The South Fork travels about 3670 linear feet on the central campus, dropping about 110 feet in elevation for an average gradient of 3 percent. Likewise, the Main Branch runs about 450 linear feet from the Eucalyptus Grove the entrance of the city tunnel at Oxford Street, dropping 15 feet, or about a 3 percent grade.
The North Fork subwatershed comprises 388 acres (0.6 mi2). It is bounded by Little Grizzly Peak on the east, Rose Street on the north, and the South Fork subwatershed to the south. The North Fork, which originally drained just Blackberry (Woolsey) Canyon, has also been identified as Blackberry Creek, although this is a misnomer because another creek in North Berkeley has that name. Due to stormwater routing, the channel above Highland A venue now drains a large portion of the LBL complex, Lawrence Hall of Science, and Space Sciences Laboratory, extending all the way to Grizzly Peak Boulevard. Much of the North Fork has been culverted underneath the LBL complex and North Berkeley. An extensive artificial fill area is located in the original creek channel north of the Lawrence Hall of Science and cut and fill operations also obliterated the original North Fork channel throughout the LBL complex. Open channels along the North Fork still exist in Blackberry Canyon below LBL, between a few blocks in North Berkeley, and on the central campus.
The open channel in Blackberry Canyon dumps into a drop inlet above Highland Avenue. During low flow periods, the creek is directed into an open channel south of Le Conte Avenue which enters a tunnel under Northside and empties into the central campus at North Gate. At times of high flow, most of the water in the North Fork is diverted into a 48"- 60" storm drain culvert which runs down Ridge Road to Euclid Avenue and thence to the creek at North Gate.
The North Fork watershed has been extended beyond its natural drainage area to the north due to stormwater routing. Euclid Avenue and La Loma Avenue storm drain lines extend as far north as Rose Street. These storm lines eventually dump into the North Fork city tunnel which empties into the open channel on the central campus at North Gate.
The North Fork then meanders through the northwest portion of the central campus and is routed underneath West Circle into the Eucalyptus Grove where it meets the South Fork. The North Fork travels·approximately 2150 linear feet on the central campus, dropping about 80 feet in elevation for an average grade of 4 percent. This is slightly steeper on the average than the other central campus reaches of the creek. The cross-campus culvert empties into the North Fork just above the University Drive vehicle bridge. This culvert drains the northeastern section of the central campus, continues eastward under Gayley Road by Stem Hall, and across Cyclotron Road to the Cafeteria Creek channel which drains a small portion of the LBL complex. The cross-campus culvert is the single largest point source on campus in terms of both drainage area and volume of effluent.
The remaining 16 acres of the upper Strawberry Creek watershed drain directly into the Main Branch of the creek above Oxford Street. Much of this area consists of Evans Field and Edwards Track Stadium drainage which is routed directly into the Main Branch.
The upper Strawberry Creek watershed generally lies in the California Coast Ranges section of the Pacific Border physiographic province. The steep southwestward-facing front of the Berkeley Hills trend northwestward at the head of Strawberry Canyon. The Hayward Fault roughly parallels Gayley Road, forming the toe of the hill slope. West of Gayley Road the land surface including the central campus gently slopes west-southwestward towards San Francisco Bay.
The topography of Strawberry Canyon is almost totally fault-controlled. Along with related severe erosion this has formed the existing canyon and drainage system east of the Hayward Fault. Canyon topography consists generally of a complex pattern of relatively small secondary ridges and nosings separated by an intricately branching canyon system which resulted from a combination of faulting and erosion. Except for lower Strawberry Canyon, the area is generally steeply sloping, averaging about twenty-five percent The existing extensive level areas in the canyon are a result of construction grading activities. Elevation ranges from about 1760 feet at the crest of the Berkeley Hills down to 200 feet at the west end of the central campus (Oxford Street), constituting a drop of over 1500 feet in elevation in the upper watershed.