The Strawberry Creek Management Plan
Robert B. Charbonneau
Office of Environmental Health and Safety
University of California at Berkeley
Strawberry Creek represents an irreplaceable natural resource that is highly valued by both the University and community at large. The riparian corridors along the creek are the focus of central campus open space. These areas offer natural contrast to the urban hardscape, acting as a buffer zone which provides visual amenity and variety. The creek corridors also provide essential places for educational, recreational, social and individual activities. Strawberry Creek's value as an educational resource is enhanced by its accessibility and proximity to classroom facilities.
The upper Strawberry Creek watershed located above Oxford Street in Berkeley, CA is composed of two major branches, the North and South Forks. The total watershed area is 1163 acres or 1.8 mi2. Stormwater routing as well as stream culverting and channel confinement have significantly altered the natural drainage courses of both forks. The two forks converge at the Eucalyptus Grove on the central campus to form the Main Branch.
The watershed is approximately 40% urbanized, primarily by institutional land uses in the western portion of the watershed. Urbanization has had a profound impact on the hydrologic regime of Strawberry Creek. A significant amount of impervious surface area in the watershed in addition to culverting and confinement of the natural creek channels and stormwater routing have combined to create a very flashy hydrologic regime. The resulting high peak storm flows have accelerated streambank erosion and led to the destruction of aquatic habitat.
Low flow water quality of Strawberry Creek is fairly good in the canyon areas but has been degraded in the urbanized downstream reaches by eutrophic nutrient levels and fecal bacterial contamination. Sewage contamination on the central campus is a major problem. Point source effluent also significantly alters the water chemistry of the North Fork on the central campus. This is due to extensive dilution of natural stream flow levels with point source effluent, predominantly cooling water. Streamflows are doubled by the addition of point source effluent on the central campus during low flow periods.
Stormwater runoff from the entire watershed is routed directly into Strawberry Creek causing significant degradation of water quality. Runoff from streets, parking lots and other urban land surfaces concentrates debris and pollutants deposited by a myriad of sources in the urban environment This results in substantial increases in chemical oxygen demand, suspended solids, turbidity, organic nitrogen, phosphorus, total and fecal coliform bacteria, as well as trace metals in Strawberry Creek during wet weather. Non-point sources of pollution have a significant short-term "shock loading" effect on the water quality of the creek.
Creek management strategies consist of point source pollution controls, grade control and streambank stabilization measures, as well as riparian and aquatic habitat restoration techniques. The sources of direct discharges into Strawberry Creek need to be further investigated. All wastewaters should be routed to the sanitary sewer system. Rehabilitation of existing grade control structures is essential to prevent further downcutting of the streambed which leads to streambank undercutting and scouring of the streambed. Biotechnical streambank stabilization techniques should be applied in applicable areas to deal with existing bank erosion problems. Management guidelines need to be evaluated and implemented for the designated central campus nature areas which coincide with the riparian corridors of Strawberry Creek.
Best management practices need to be instituted for non-point source pollution control. Priority should initially be given to implementing non-structural stormwater management techniques. An annual monitoring program would enable the continuing evaluation and redefinition of water quality problems.
Environmental management of Strawberry Creek must be far-sighted and comprehensive in scope in order to adequately protect and enhance the creek and its associated riparian areas. The recently formed Creek Environmental Quality Committee should form the basis for long-term management. A multitude of approaches including the updated Long Range Development Plan, environmental impact reports, RFP conditions, and Department of Facilities Management policies and directives can be utilized to ensure consideration of the environmental concerns identified in this report in the campus planning process and operations.
Strawberry Creek has been neglected for many years and subsequently the environmental quality of the creek and its associated riparian areas has continued to deteriorate. The degradation of this sensitive area is evident on the central campus of the University (Figure 1). This is manifested by a marked absence of diverse flora and fauna in the creek itself and along its banks. The water is periodically discolored, foaming occurs, and other obvious signs of pollution are evident. The streambanks are undercut, threatening walls, bridges, and other structures built in close proximity to the creek. Sedimentation and turbid waters are commonplace. The variety of wildlife in the riparian areas is limited and has reportedly been steadily declining over the years (Siri, 1972).
Until the present time there has been little attempt to consider Strawberry Creek in the campus planning process. A general lack of knowledge by the Department of Facilities Management (DOFM) and the Campus Planning Office concerning the problems facing the creek and the impacts of past, present, and future activities and development has resulted in the degraded conditions apparent today. This situation has been compounded by fiscal constraints that have been placed on campus operations in recent years. A great need exists to incorporate environmental concerns surrounding the creek into the operations, maintenance, and planning processes within the University.
The Office of Environmental Health and Safety (EH&S) recognized the deteriorating environmental quality of Strawberry Creek and the lack of any comprehensive management plan. This study was subsequently initiated at the request of EH&S. The study began as a water quality management plan with the following objectives:
Evaluate present water quality of the creek.
Identify point and non-point sources of pollution.
Develop creek and watershed mitigation strategies.
Produce a resource document on which future evaluation and management decisions could be based.
Provide an overview of historical data.
In order to formulate a truly comprehensive management plan, the scope of the study necessarily expanded from strictly a water quality management plan into the areas of urban creek and riparian habitat preservation and restoration.
The benefits of preserving and enhancing Strawberry Creek and its riparian areas are multi-faceted. The visual and experiential image of the Berkeley campus is manifested by its physical setting which is dominated by the features and character of its landscape. The natural areas on the central campus consist primarily of the riparian zones along both forks of Strawberry Creek. These areas offer natural contrast to the urban hardscape, acting as a buffer zone which provides visual amenity and variety. The creek is the major focus of campus open space and therefore establishes both the form and character of its landscape. Preservation is essential if the unique image and qualities of the campus are to be sustained.
The riparian corridors of Strawberry Creek provide essential places for educational, recreational, social, and individual activities. The creek functions as an integral part of instruction in the social sciences, natural sciences, and engineering. A conservative estimate of the number of students using these areas annually is about three thousand. Siri (1972) also found that at least eighteen courses in ten different departments utilized the natural areas on campus. Siri also documented the use of the riparian areas for faculty and graduate student research.
The value of Strawberry Creek as an educational resource is enhanced by its accessibility. The financial and logistical constraints of field trips, especially in introductory classes with large enrollments, are not a problem when the use of Strawberry Creek is considered. The time limitations of travel elsewhere also promote the increased utilization of the creek areas. The creek is also valuable for spontaneous use for the purposes of illustration, demonstration, and repeated observations. In addition, Strawberry Creek offers everyone an informal educational opportunity through exposure, experience, and chance observation. It is obvious that the creek and its associated riparian corridor represent a significant teaching resource that warrants attention, maintenance, and enhancement.
Creek and Watershed Description
This section provides a description of the physical and natural setting of
Strawberry Creek and its upper watershed. This section also contains an
historical overview of development in the watershed and its subsequent
impacts, as well as descriptions of the watershed soils and geologic
This study deals with the upper Strawberry Creek watershed which lies east of Oxford Street in Berkeley. 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 square miles). 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 Avenue 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 Stern 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.
This abbreviated history gives an indication of the adverse impacts development has had on Strawberry Creek. A long history of water quality problems, flooding, and erosion becomes apparent. Extensive diversions and stream course channelization and alterations have occurred over the past eighty years. Construction costs for storm drainage systems and flood damage to the University over time has been quite significant.
Prior to the arrival of the Spanish and other white settlers to California in the late 1770's, native Indians of the Huchiun-Ohlone group lived in clustered settlements along streams such as Strawberry Creek. They once maintained a summer camp near the present site of the stadium. The Indians were hunter-gatherers who managed their land by controlled burning of the underbrush to facilitate acorn gathering and the growth of seed-bearing annuals. The landscape appeared as an open oak woodland and grassland filled with perennial bunch grasses and herbaceous flowering plants. Much of the tree cover was limited to the stream channels, and strips of riparian vegetation closely followed the steam corridors from the crests of the hills down to the alluvial flatlands. Deer, elk, bear, and mountain lions were abundant in the hills. Salmon and trout spawned in the upper reaches of the creeks.
On March 27, 1772, a Spanish scientific expedition led by Don Pedro Fages stopped along the banks of Strawberry Creek just upstream of present-day Oxford Street. From this future site of the University, diarist Juan Crespi described the beauty of the Golden Gate vista. Legend has it that the creek got its name from the abundant strawberry vines that lined its banks. Spanish explorers named the East Bay area "Contra Costa" or "opposite coast". In the early 1800's much of the East Bay was partitioned into land grants by the last Spanish governor of California. The boundaries of these tracts were often delineated by streams because they were the most obvious landscape elements. The Rancho San Antonio tract which was deeded to Don Luis Maria Peralta in 1820 encompassed the present cities of Albany, Berkeley, Emeryville, Alameda, Oakland, Piedmont, and San Leandro. In 1842, Peralta divided the Rancho among his four sons, and gave his son Jose Domingo the area now called Berkeley.
The Gold Rush of 1849 opened the East Bay to land development booms. The Berkeley area bore the brunt of the influx of American settlers as development spread across the Bay from San Francisco. Jose Domingo Peralta resisted the first American squatters, but soon realized he could not maintain control over such desirable land. In 1853, Peralta sold off most of his land and the next year Orrin Simmons, a sea captain turned farmer, acquired squatter's rights to 160 acres of land between Strawberry Creek and the present Clark Kerr campus. In 1857, he obtained full title and purchased two more tracts of land, giving him ownership of 700 acres including the future site of the University campus.
In 1860, the College of California moved to its present site from Oakland. Strawberry Creek was one of the main reasons the founders chose Simmons' property. "All the other striking advantages of this location could not make it a place fit to be chosen as the College Home without this water. With it every excellence is of double value" (Willey, 1887). Even during a drought in 1864 the stream continued to flow the entire year, yielding about 100,000 gallons a day or about 0.16 cfs. Three forks of Strawberry Creek meandered through the college site at that time. The middle fork was drained in the early 1870's to create a dry level area for a cinder running track now occupied by the Life Sciences Building Annex. To protect the track from strong westerly winds, the Eucalyptus Grove was planted.
The central campus at this time was a sloping grassy plain dotted with coast live oaks. Oaks, sycamores, bay trees, and shrubs lined both forks of Strawberry Creek. Old photographs reveal considerable tree planting during the 1860's and 1870's in an apparent effort to improve the barren landscape. Cattle were introduced into the hill area in the 1850's and grazed on imported annual grasses which quickly established themselves. Eventually these grasses out-competed the native perennial bunch grasses which could not survive the impacts of heavy grazing. Dairy farms were located in Strawberry Canyon before the land became part of UC holdings in 1909 and cattle continued grazing in the hills until the 1930's. Grass-oak savannah was the vegetative cover in the canyon as shown in photographs taken in 1870 and 1901. The East Bay creeks supported a growing timber trade that significantly depleted the tree cover of the upper creeks. This was especially true during the rebuilding period which followed the 1906 San Francisco earthquake and fire. Eucalyptus was often planted throughout the East Bay hills in the early 1900's by small private water companies as a means of profiting from the shortage of California hardwood lumber at the time.
Waterworks were constructed in Strawberry Canyon in the 1860's to supply water to farms and speculators. Springs were developed, pipes laid, and wooden flumes constructed to carry the water. In 1867, a brick reservoir was constructed in the canyon and waterworks placed to deliver more water. Up until this time the cleared land in the canyon was divided amongst a few farmers. As additional land was cleared in the canyon, runoff from the hills increased, causing severe erosion downstream. In October of 1882 the University built five check dams along Strawberry Creek in an attempt to stop streambed incision and subsequent bank erosion on the central campus.
In 1883, the first large culvert was installed in a small stretch of streambed in the vicinity of Oxford Street to facilitate the passage of horses and wagons. Cement box culverts were installed along the creek throughout its entire length in Berkeley during the late 1800's and early 1900's. This culverting continued until the 1930's when the Works Progress Administration (WPA) finished culverting the last open reaches. The entire length of Strawberry Creek through the city of Berkeley was now underground.
The first report of water quality problems appears in the Berkeleyan in 1895. An article complains of the "unsightly appearance of sewer-begrimed water and filthily discolored banks." Strawberry Creek was noted as being an easy means of removing sewage. In 1900, the Benard Plan for the campus layout originally called for the removal of the creek from the grounds, but was later revised after objections were raised. A storm in March 1904 caused $300 damage to culverts on the central campus and extensively damaged streambanks. This prompted rock and concrete work in many locations along the creek to stabilize the banks. USGS experiments conducted in 1907 estimated that one ton of soil was being carried away for every 12,000 gallons of winter storm flow.
Extensive concrete work was performed on the entire creek in 1907 to protect streambanks and trees. Both the creek sides and bottom were lined with concrete. The creek was also deepened five feet in the reach upstream of Oxford Street in an attempt to avert the flooding of downstream commercial areas which occurred the previous winter. The construction of Memorial Stadium in 1923 necessitated the first major diversion of Strawberry Creek. The stadium obliterated waterfalls that once cascaded down the toe of the hillslope and resulted in the construction of the "Little Inch" bypass culvert to carry the creek underneath the stadium and Strawberry Field. The construction of Stephens Hall that same year also required the rerouting of the original creek channel.
The "Big Inch" bypass culvert was built in 1951 at a cost of $225,000 due to the possibility of structural failure of the Little Inch bypass. Cracks were discovered in the old culvert from the stress caused by the Hayward fault zone. At that time, the Big Inch culvert began just above the Haas pools and emptied out next to the Faculty Club on campus.
Rains in April 1958 caused $70,000 damage to Canyon roads and drainage systems. International House was flooded and landslides blocked Canyon fire trails. Only four years later in October 1962, 15 inches of rain fell in four days, making it one of the heaviest storms ever recorded in the San Francisco Bay area. The Big Inch bypass inlet clogged with debris and the torrential creek overflowed through the Haas complex and down Centennial Drive. Damage to campus buildings and grounds was estimated at over $200,000. As a result of flooding of the Dining Commons in 1963, a 300 foot reach of the South Fork from Sather Gate to the Dwinelle Annex was widened to ten feet and a concrete retaining wall was built along the south bank. In Fall 1964, the University spent $519,000 on storm drain improvements. This action was necessary because of the development in Strawberry Canyon that had reportedly reduced the lag time (the time response of runoff to precipitation) to the bypass culvert entrance in the canyon from about two hours to fifteen minutes, posing a great threat to the campus by significantly increasing the peak storm flow.
In 1966, the University extended the Big Inch bypass inlet to an earthen retention dam built in the canyon at the entrance to the Lower Fire Trail. The retention basin would act to store flood waters during winter storms and flow could be regulated into the bypass culvert by means of a hydraulically operated gate. This structure would act to prevent the extensive flooding and damage that occurred in 1962. Also in 1966, a high flow bypass was built into the North Fork city tunnel system to relieve the flooding threat caused by increased runoff from LBL development in the canyon. These storm drain improvements were done at a cost of $145,000 which was shared by the City and the University.
Various newspaper articles in the 1970's and 1980's relate the continuing water quality problems in the creek. A 1973 article tells of fecal bacteria contamination entering the North Fork from the Northside area. Continued erosion of stream banks is also mentioned. A 1981 article states that the creek is treated as a sewer contaminated by urban runoff, chemicals, drains, and sewage. Berkeley Health Department officials advised not to enter the creek at that time.
The USDA Soil Conservation Service (SCS) Soil Survey of Western Alameda County was used to delineate the soil types of the upper Strawberry Creek watershed. The soil types are presented in Table 2 and shown on Figure 3. Soil series may be assessed for their runoff potential, risk of erosion, and other parameters of concern in the management of Strawberry Creek and its watershed. In general, the upper watershed soils are highly impermeable and have a high runoff potential as well as a high risk of erosion. Strawberry Canyon is the site of numerous landslide bodies that will easily slide when undercut or flow when saturated. Development on the Canyon soils is severely constrained by steep slopes and shallow depth to bedrock.
Hydrologic soil groups as defined by the SCS can be used to estimate runoff potential of each soil type in the watershed based upon its infiltration capacity. Infiltration rates decrease and surface runoff potential increases as soil types are classified A through D. Approximately 38% (431 ac) of the watershed consists of soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. Soils having a very slow to slow infiltration rate comprise about 23% (234 ac) of the watershed, whereas 1% (18 ac) of all the watershed soils have a slow infiltration rate. Soils with a very slow to moderate infiltration rate account for 20% (234 ac) of the watershed. The remaining 18% (209 ac) of the watershed area is unsuited to the hydrologic soil classification system because it is covered by urban structures or comprised of heterogeneous artificial fill materials.
Three different soil types account for 75% (736 ac) of the upper Strawberry Creek watershed area. Maymen loam is the predominant soil type in the watershed (366 ac or 32%). This is a shallow (10-20 in) somewhat excessively drained soil with rapid to very rapid runoff potential and high to very high risk of erosion. It is found on upland areas with slopes of 30-75%. The pH range of Maymen loam is strongly acid (4.5-6.5). This soil type formed in material that weathered from sedimentary rock. It is generally underlain by sandstone, siltstone, and conglomerate.
The Maymen-Los Gatos complex is another dominant soil type in the watershed, comprising 265 acres (23%). This complex consists of steep and very steep soils on uplands. Slopes range from 30-75%, but are mainly 50-75%. This soil complex is composed of 50% Maymen soils and 35% Los Gatos soils. The remaining 15% of this soil type are small areas of Millsholm silt loam and some rock outcrop. Depth to bedrock ranges from shallow to moderately deep (10-40 in). Runoff and erosion characteristics are identical to Maymen loam. The pH of this complex ranges from strongly acid to neutral (4.5-7.3). The Maymen-Los Gatos complex formed in material that weathered from sedimentary rock and is underlain predominantly by sandstone and shale.
The last major soil type is the Xerorthents-Millsholm complex which comprises 20% of the watershed area. This complex is on hills at slopes ranging from 30-75%. It consists of about 70% loamy Xerorthents (altered soil or fill material), 20% Millsholm clay, and 10% of small areas of Maymen loam, Los Gatos loam, and Los Gatos silty clay loam. Depth to bedrock ranges from shallow (10-20 in) to over 20 inches. This complex is well to somewhat excessively drained. Runoff is rapid to very rapid and risk of erosion is high to very high. The pH of this complex ranges from medium acid to slightly alkaline (5.6-7.8). The xerorthents in this complex consist of soil materials that have been altered by cutting or filling for urban development and, as a result, they have variable soil characteristics. The Millsholm soil formed in material that weathered from fine-grained sandstone. This soil complex is generally underlain by sandstone, siltstone, and undivided Quaternary deposits.
The upper Strawberry Creek watershed consists mostly of the geologically very recently uplifted Berkeley Hills which hinge along the northwest trending Hayward fault zone. In general, the steep hill area is unstable and bedrock is close to the surface, resulting in numerous landslides and extensive soil erosion. The hill area is part of a very complex volcanic vent structure that has been truncated and displaced northward by the Wildcat Fault. West of the Hayward fault zone is a gently westward sloping older alluvial plain which has been altered in the Central Campus and LBL areas by cut and fill construction activity. The subsoil in the Central Campus consists of soft, highly erodable stream sediments grading from clayey silts to cobbles and boulders. These sediments exhibit very poor stability along the banks of Strawberry Creek.
The bedrock in the Canyon grades time-wise from Upper Cretaceous marine sediments through Miocene sediments (Claremont Formation) to the late Pliocene sediments and volcanics of the Orinda, Moraga, Grizzly and Bald Peak Formations. A series of earth movements extensively folded and faulted these formations and massive volcanic intrusion has further altered the bedrock. The resultant formational contacts are steeply sloping to vertical and the time sequence is thus commonly horizontal rather than lying in vertical succession. The character of the rocks varies widely, ranging from fairly hard sandstones in the Cretaceous series to soft and clayey semi-shales of the late Pliocene deposits. The volcanic members vary from extremely hard but generally intensely fractured basalts to soft tuffaceous sediments.
The Upper Cretaceous rocks underlie about 16% (186 ac) of the watershed between the Hayward and Wildcat Faults bordering both sides of Strawberry Creek. These sediments are the oldest rocks in the hill area, consisting of fragments of older rocks which have been significantly altered and fractured by tectonic movements. These rocks are moderately to highly weathered, soft to medium hard, and locally folded. This unit weathers fairly easily, producing thick residual soils that often migrate downhill by landslides or by colluvial processes.
Most of the northern area of the watershed between the Hayward and Wildcat Faults is underlain by the Moraga-Grizzly Peak-Bald Peak Formations (180 ac). These are extrusive igneous rocks that have been altered by shearing and weathering, and are highly fractured. These formations are permeable enough to permit rapid and extensive water circulation. Generally, the rocks are medium to completely weathered, soft to medium hard and very thickly bedded. The Grizzly Peak unit is slightly weathered and very hard with medium-spaced (8-24 inches) fractures.
East of the Wildcat Fault lies the Claremont Formation (163 ac) which consists mainly of thin bedded shales and siltstone of moderate hardness. The rocks are generally fairly siliceous or have an appreciable calcite content and are thus relatively hard, resistant to erosion, and stable at quite steep slopes. Although porous, these rocks are not very permeable because pore openings are very small and poorly interconnected.
The Orinda Formation (154 ac) lies to the east of the Claremont Formation and also occurs in pockets between the Hayward and Wildcat Faults. These rocks are soft and relatively easily eroded so they are unstable at steep slopes, especially when saturated. These rocks have been extensively degraded by both tectonic shearing and intense surface weathering. The majority of the numerous large landslides in the canyon have been based in Orinda Formation materials. Hillslopes are commonly covered with a mantle of landslide debris that will easily slide when undercut or flow when saturated. Debris or mudflows in the canyon pose a major hazard because obstructions may clog inlets to the storm drain system and divert flow out of normal channels, resulting in extensive damage. Much of upper Centennial Drive and parts of the Lawrence Hall of Science are located on the Orinda Formation, as well as most LBL facilities.
The last major geologic unit in the watershed is the Moraga Formation (126 ac) which is located mainly in the steep northeastern hill area. These rocks are generally hard, but intensely fractured due to both natural shrinkage processes upon cooling and tectonic movements which occurred after deposition. Permeability is therefore generally high. The Moraga Formation is stratigraphically and topographically the highest bedrock unit in the hill area, capping the upper hills and the Grizzly Peak ridgeline on the northeastern boundary of the watershed.
Numerous landslides occur in the hill area, especially in the vicinity of the LBL complex. These slides are composed of substantial soil and rock masses that have slid downslope along a failure plane. They may occur rapidly in a single major event or slowly through repeated small failures. New or old slides may be precipitated by high groundwater levels, ground shaking, or changes in slope geometry and loading. Slides can often be recognized by a bulging, cracked "toe" at the lower end, and by arched headscarps and topographic depressions at the upper end. In the Berkeley Hills some thick mobile accumulations of colluvium (soil and rock fragments transported downslope by gravity) closely resemble shallow landslides, making it difficult to distinguish between them. Most older landslides are marked by heavy brush and tree cover because the vegetation prefers the relatively soft wet soil found there.
The Hayward fault zone is a member of the San Andreas Fault system which is a major geologic feature and plate boundary along which massive continental drift is presently occurring. The Hayward fault zone forms a distinct geologic break between the Central Campus area to the west and the hill area to the east. The Wildcat Fault is another significant geologic feature in the watershed, and is probably a secondary member of the San Andreas system. This fault traverses the Canyon in the vicinity of the Botanical Garden.
The Hayward fault exhibits right-lateral movement, with the westerly side moving to the northwest in comparison to the easterly side. Slow tectonic creep (movement) is presently continuing along the fault at the rate of about 0.1 inch per year in the area of Memorial Stadium. The "Little Inch" Strawberry Creek drainage culvert under the stadium has been previously damaged by this movement.
Tectonic creep has produced major tension and compression faults east of the Hayward fault zone and the tectonic movements which caused the uplift of the Berkeley Hills has produced thrust faulting as well. The result is a complex system of cross-faults with both vertical and lateral movement. One such secondary fault has formed the canyon of the South Fork of Strawberry Creek above the stadium. These faults range in size from very small breaks to the Hayward fault zone, which is several hundred feet wide.
The Hayward fault zone can be assumed to the active along its entire length.
Severe earthquakes were caused by movement along faults within the Hayward fault
zone in 1836 and 1868. Ground rupture was reported across the west side of the
Clark Kerr campus and northwestward between Prospect and Warring Streets. Future
movement within the Hayward fault zone may or may not follow the same fault
trace. The trace should not be construed as indicating the only line within the zone where movement has taken place in the past, nor is it necessarily the line where movement will occur in the future.
Structures which lie within or across the Hayward fault zone may not only be damaged by sudden movement, offset, and rupture along a fault in the event of an earthquake originating in the fault zone, but may also be subject to constant strain and damage due to opposite sides of faults within the zone continuously moving very slowly in opposite directions.
The Wildcat Fault is also a right-lateral fault with apparently local vertical movements. This constitutes another major structural non-conformity in the watershed. This fault has undoubtedly been active in relatively recent geologic time. Whether creep is currently occurring along the fault or whether there is currently any hazard of displacement is not known with any degree of certainty. East of the Wildcat Fault the secondary fault pattern continues with less expression, apparently reflecting lesser total long-term movement. These secondary faults are presumably currently inactive. The fractured rocks along any of these faults form numerous passages for groundwater.
The most recent geologic studies of the complex hill area (Converse Assoc., 1984) suggest that a single deep groundwater table may exist in combination with numerous perched groundwater tables. The perched groundwater areas may exist seasonally or only after periods of heavy rainfall. The local presence of groundwater in the hill area is also strongly influenced by the presence of seepage barriers such as faults and the numerous Orinda-Moraga formational contacts. The primary sources of groundwater in the hill area were deduced to be surficial (runoff and infiltration) as well as the volcanic flow rocks east of the Wildcat Fault.
Groundwater may move relatively freely through the highly fractured Moraga rocks, but is impeded by the relatively impermeable contact zone and less permeable nature of the Orinda rocks. This restriction of groundwater flow results in an accumulation of water at and above the contact zone of these two formations. Flow occurs along these contact zones when gradients are sufficient and often exits the hillsides in the form of springs or seeps. A strong correlation exists between spring locations and Orinda-Moraga contacts. These contacts are highly irregular because of the interbedded nature of these formations, so springs do not occur at any given elevation on the hillsides.
Chemistry of Water