Lower Alameda Creek Watershed
OverviewThe 660-square-mile Alameda Creek Watershed is the largest watershed in the Bay Area. It extends as far south as Mount Hamilton, north to Mount Diablo, east to the Altamont Hills in Livermore, and west to San Francisco Bay. The information in this watershed page focuses on the Lower Alameda Creek Watershed. This portion of the watershed makes up just 6 percent of the total watershed area and is located in western Alameda County within the Alameda County Flood Control and Water Conservation District’s (the District) jurisdiction. This 41-square-mile portion includes the Walpert Ridge area of the East Bay hills and the flatlands of Fremont and Union City. The flatlands were created by Alameda Creek itself, each successive flood laying down another layer of sand, silt, and gravel to form a large alluvial fan that slopes gently bayward.Downloads: Overview map (PDF) | Lower Alameda Creek Watershed map (PDF)
Flora and FaunaThe Agua Fria Watershed drains the Diablo Ridge across grassland hills where cattle graze under the occasional coast live oak, valley oak, blue oak, Mexican elderberry, and Pacific madrone. Common trees in the riparian corridors include white alder, California sycamore, and willow. California poppies, monkey flowers, and lupines are prevalent wildflowers during the spring. The East Bay Regional Park District publishes a wild plant checklist for all plants found within Mission Peak Regional Preserve located in the watershed. Many small mammals and a population of coyotes inhabit the Mission Peak ridgeline area. The Diablo Range garter snake, which closely resembles the California garter snake, is also common.The Agua Fria drainage flows into Coyote Creek, which, from aerial photos of south San Francisco Bay, appears as the longest of several twisted tendrils extending inland through a maze of salt ponds and restored tidal marsh. The marsh plain is part of the Don Edwards San Francisco Bay National Wildlife Refuge—home to nesting shorebirds as well as 45,000-75,000 migrating waterfowl. Two reports provide specific details on San Francisco Bay salt pond and tidal marsh habitats: a policy background report from the San Francisco Bay Conservation and Development Commission; and from the San Francisco Estuary Project, a habitat assessment as part of a bay-wide collaborative effort to identify habitat goals.
Geology and HydrologyThe Agua Fria Watershed drains through Miocene epoch sedimentary rock on the west side of the Diablo Ridge and then through Pleistocene epoch sediments to I-680. The drainage is directed into culverts under I-680, which parallels the Hayward Fault. During the Pleistocene epoch, a large river flowed through this area to what is now south San Francisco Bay. Movement along the Hayward Fault interrupted the river flow, creating many creeks. In the last several thousand years, these creeks flowed to the bay across a wide marsh plain thick with vegetation and branching waterways. The process that formed south San Francisco Bay tidal marshes is explained in detail in the Mowry Slough section.
Major IssuesWater contamination levels in the Agua Fria Watershed are consistent with urban areas in the region. Mercury, PCBs, and PBDEs are the greatest concerns, while dioxins, pyrethroids, PAHs, and selenium are also problematic. Though overwhelming evidence demonstrates the potential of tidal marshes to improve water quality, the large-scale restoration activities in the South Bay may have their own adverse water quality impacts. These are detailed in a study by the San Francisco Estuary Institute. In the course of the restoration effort, the potential impacts are identified, mitigated where possible, and addressed through an adaptive management approach.
(The following information pertains to the Lower Alameda Creek Watershed within the jurisdiction of Alameda County Flood Control and Water Conservation District – from the mouth of Niles Canyon to San Francisco Bay.)Seven creeks and flood control channels drain to the Alameda Creek Flood Control (ACFC) Channel in western Alameda County, forming significant subwatersheds within the Lower Alameda Creek Watershed, as described below. The north and south forks of Dry Creek drain the hills north of Niles Canyon; Crandall Creek drains the flatlands south of Alameda Creek; The District’s Zone 5, Line J2 drains the flatlands north of Alameda Creek; and Ardenwood Creek, within the Crandall Creek subwatershed, drains the floodplain between Crandall Creek and the managed ponds and wetlands, or “baylands,” of San Francisco Bay.
Lower Alameda Creek SubwatershedLower Alameda Creek is a 11 square-mile subwatershed comprised of the portion of Alameda Creek located in western Alameda County that begins near the mouth of Niles Canyon. From this point, Alameda Creek flows through the 12-mile-long Alameda County Flood Control Channel constructed by the Army Corps of Engineers in the 1970s. The channel passes through Union City and Fremont across the creek’s historic flood plain, then flows north of Coyote Hills Regional Park before reaching San Francisco Bay. With the construction of the flood control channel, Alameda Creek was diverted south of its historic route. Although the historic channel was left intact to form Old Alameda Creek, the western portion of the Alameda Creek Watershed bisected into north and south – old and new. For more information on the Old Alameda Creek Watershed, click here.
Dry Creek SubwatershedDry Creek is a 9.9-square-mile subwatershed that drains Walpert Ridge in the East Bay hills north of Niles Canyon. The north and south forks of Dry Creek meet near the terminus of Tamarack Drive in Union City. Both forks of Dry Creek run through Garin and Dry Creek Pioneer Regional parks, and through most of the subwatershed Dry Creek remains in its natural condition before its confluence with the ACFC Channel.
Crandall Creek SubwatershedCrandall Creek is a 6.5-square-mile subwatershed comprised of Crandall Creek and Ardenwood Creek that once drained the floodwaters across the floodplain south of the historic Alameda Creek channel. Historically, Ardenwood Creek joined Crandall Creek just north of Coyote Hills, draining a riparian corridor thick with willows. From the point its confluence with Ardenwood Creek, Crandall Creek made a straight shot across the flatlands to the extensive tidal marsh that rimmed the south bay. Its former outflow to the bay is now the outflow of the ACFC Channel.One of the area’s largest and most productive historic farms, the Patterson farm, was located along Ardenwood Creek in what is now Fremont, taking advantage of the fertile soils in the alluvial fan of historic Alameda Creek. The Patterson family house and farm are now preserved as part of Ardenwood Regional Preserve. Commercial farming continues today at both Ardenwood and adjacent properties.Today Crandall Creek and Ardenwood Creek drain urban runoff through a series of culverts and engineered channels that flow into the Demonstration Urban Stormwater Treatment (DUST) Marsh, an artificial wetland designed to treat urban runoff, before eventually leading to San Francisco Bay. Its former outflow to the bay is now the outflow of the ACFC Channel.
Zone 5, Lines J2 & J3 SubwatershedZone 5, Lines J2 and J3 drains a 1.9-square-mile subwatershed in a residential area of Union City near the managed ponds and wetlands of south San Francisco Bay. A series of culverts drain to an engineered channel that joins the ACFC Channel.The shallow waters of south San Francisco Bay provided excellent conditions for the extensive tidal flats and tidal marshes that rimmed the shoreline. These same conditions made the south bay an excellent place for salt farming. Small scale salt production was a traditional activity of the Ohlone Native Americans, the Spanish, and early American settlers. From the mid-1800s through the late 1900s, salt production expanded to include large industrial ponds that transformed the south bay tidal flats and tidal marshes. In 2003, most of the salt ponds were purchased for restoration and are now part of the South Bay Salt Pond Restoration Project managed by the California Coastal Conservancy. Due to natural subsidence and that induced by salt production, many of these ponds will remain behind levees as either restored areas, managed tidal marshes, or managed ponds, all of which provide valuable habitat.
(The following information pertains to the Lower Alameda Creek Watershed within the jurisdiction of Alameda County Flood Control and Water Conservation District – from the mouth of Niles Canyon to San Francisco Bay.)From Niles Canyon to the bay, there are two city parks, four regional parks, and a 12-mile-long regional trail within the Lower Alameda Creek Watershed. The parks provide water-oriented recreation, hiking, bicycling, and nature study and preserve the rich agricultural traditions in the former Alameda Creek floodplain. After flowing through parkland and urban developments, the Alameda Creek Flood Control (ACFC) Channel enters the bay through the Don Edwards San Francisco Bay National Wildlife Refuge.
TrailsThe Alameda Creek Regional Trail extends 12 miles along the levee of the Alameda Creek Flood Control (ACFC) Channel from the mouth of Niles Canyon in Fremont to San Francisco Bay. The trail connects with Quarry Lakes Regional Recreation Area, Coyote Hills Regional Park, and the Don Edwards San Francisco Bay National Wildlife Refuge. Used most by cyclists, the entire trail along the south side levee is paved, including a loop that circles Coyote Hills.
Parks and Recreationhere.
Alameda Creek Fish Habitat RestorationThe restoration of ocean-run steelhead trout began in 1999 as a collaborative effort between the Alameda County Flood Control and Water Conservation District and several other agencies. It has been an extensive, ongoing project involving the removal of three dams and the construction of fish passage structures such as fish ladders. Stream flows will be improved for cold water fish, and habitat along the flood channel will be restored. With the completion of these projects, anadromous fish will be able to access up to 20 miles of spawning and rearing habitat in Alameda Creek and its tributaries.
South Bay Salt Pond Restoration ProjectThe 15,100 acres of industrial salt ponds in south San Francisco Bay will be restored through the South Bay Salt Pond Restoration Project, the largest tidal wetland restoration project east of the Mississippi River. The baylands at the outflow of ACFC Channel are included within this area. Their restoration will create a diverse habitat of tidal marsh and managed ponds for fish, waterfowl, and other wildlife. Phase I of the project restored Eden Landing at the mouth of Old Alameda Creek, just north of the ACFC Channel. As part of Phase II, levees will be modified near the lower reach of Alameda Creek to help create new tideland areas. Bay tides flowing in and out of the lower segment of Alameda Creek will scour sediment that might otherwise require dredging. The restoration of tidal marsh habitat is crucial to the survival of salmonids and marsh-dependent fish. Consequently, groups like the Alameda Creek Alliance are working to ensure that the salt pond restoration compliments the restoration of steelhead in Alameda Creek.
Resources in the Watershed
- Alameda County Clean Water Program
- Alameda County Resource Conservation District
- East Bay Regional Park District
- Don Edwards San Francisco Bay National Wildlife Refuge
- Oakland Museum of California’s Guide to Bay Area Creek
- San Francisco Estuary Institute
- City of Fremont
- Math/Science Nucleus
- South Bay Salt Pond Restoration Project