The Dutch Slough site offers an opportunity for large-scale tidal marsh restoration, habitat enhancement and open space preservation in the rapidly urbanizing area of eastern Contra Costa County. During the past twenty years, eastern Contra Costa County has undergone a rapid urbanization, and in 1997, the county approved a development agreement for this property that would have allowed for the construction of 4,500-6,100 housing units on the site. When the City of Oakley incorporated in 1999, the Dutch Slough property was within the city limits, and the City was required to accept the County’s development agreement. In the fall of 2001 the Natural Heritage Institute (NHI) and the Department of Water Resources identified this site as an important restoration opportunity and began working cooperatively with the former landowners to obtain grant funding to acquire and restore the property. The 1,166-acre site was purchased in 2003, and restoration planning was still ongoing as of 2006. Restoration activities are expected to last at least 30 years, and the project will be conducted using an adaptive management framework, whereby management actions will be designed to test hypotheses about the ecosystem and the most effective strategies for its restoration. In this way, the project will yield valuable insight into the processes governing restoration and will increase our overall understanding of the science.
Dutch Slough, California, USA, 38.0128016, -121.65433389999998
Country or Territory:
United States of America
Estuaries, Marshes & Mangroves
Area being restored:
Natural Heritage Institute (NHI) and Department of Water Resources
NGO / Nonprofit Organization
Primary Causes of DegradationAgriculture & Livestock
The three parcels that comprise the Dutch Slough site were diked and drained for agriculture during the nineteenth century, perhaps as early as the 1850’s. Emerson, Little Dutch Slough, and the eastern portion of Dutch Slough are all artificial channels that were dredged between 1904 and 1910. These artificial channels displaced a pre-existing channel network that was more sinuous and irregular.
Reference Ecosystem Description
Before European colonization, the Sacramento and San Joaquin rivers and their tributaries carried water, sediment, nutrients, other dissolved and suspended constituents, wood, organisms, and other debris from basins (of more than 25,000 and 14,000 square miles, respectively) to their confluence in an inland delta, thence through Suisun, San Pablo, and San Francisco Bays to the Pacific Ocean. The channels of these rivers served as habitats and migration routes for fish and other organisms, notably several distinct runs of chinook salmon (Oncorhynchus tshawytscha), steelhead trout (0. mykiss), and Pacific lamprey (Lampetra rridenrata).
Marshes were a major feature of the lowlands of the Central Valley, especially the San Joaquin Valley, where they surrounded the huge, shallow lakes at the southern end of the valley–Lakes Buena Vista and Tulare. The Delta itself was a vast marshland, the present-day islands vaguely defined by natural levees of slightly higher ground.
The Dutch Slough site was one of these tidal marshes, and it was bordered by seasonal and riparian wetlands and Pleistocene dunes at the historic delta of Marsh Creek.
1. Provide shoreline access, as well as educational and recreational opportunities.
2. Benefit native species by re-establishing natural ecological processes and habitats.
3. Contribute to scientific understanding of ecological restoration by implementing the project under an adaptive management framework.
The project does not have a monitoring plan.
The Dutch Slough Restoration Committee has been established as a forum to exchange information, obtain input into the restoration planning and keep interested partners informed about other projects and regional issues that affect the Dutch Slough project. Key agencies and stakeholders have been invited to attend and participate on this Committee, and the meetings are open to the public.
Description of Project Activities:
The Emerson, Gilbert and Burroughs families sold the Dutch Slough properties to the California Department of Water Resources on October 30, 2003. DWR is working with the project partners and the AMWG to determine the best way to restore the site. The project partners hired a consulting firm, Phillip Williams & Associates to help develop restoration alternatives and conduct a feasibility analysis of those alternatives. Planning and feasibility studies were still ongoing as of 2006.
Ecological Outcomes Achieved
Eliminate existing threats to the ecosystem:
Restoration activities at the Dutch Slough site are only just beginning and are expected to span more than 30 years. However, preliminary site assessments and feasibility reports have offered some insights into the eventual recovery of wetland habitat at the site. What follows are some of the expected outcomes of the project. The topographic and edaphic diversity of the Dutch Slough site creates the opportunity for restoring a diversity of wetland and upland habitats. Many wetland restoration sites are intensively graded to create a mosaic of habitat types. At Dutch Slough, it would be possible to create a mosaic of wetland habitat types along a gradient from open water to dendritic tidal marsh to seasonally inundated floodplain and riparian forest without any site grading. Restoration of the site could create large areas of edge habitat including shaded riverine aquatic and riparian habitat types along the property's extensive shoreline. The site has nearly 6 miles of relatively barren levee shoreline along major tidal sloughs and Marsh Creek that could be revegetated. Tidal inundation to the interior of the site would add nearly 10 miles of edge habitat. The spatial complexity and the daily wetting and drying of the mash edges should help young salmon and splittail avoid predators and provide an abundant source of chiromindae larvae, one of the main food sources for rearing splittail and salmon (Brown, in press). Furthermore, a range of elevation gradients within a wetland site, as well as disturbance regimes associated with sediment input and other fluvial processes, result in greater biodiversity and utilization by native aquatic species (Bayley 1991). The site encompasses ten different types of organic and mineral soils. This diversity of soils will result in a corresponding diversity of vegetation and habitat types, including riparian and dune species. Coarser mineral soils will allow for establishment of woody riparian species intermixed with freshwater marsh species, while the relatively high elevation aeolian deposits of Delhi sands will provide an opportunity for restoring Antioch Dune plant species on the site. The area surrounding Dutch Slough provides habitat for numerous declining and endangered species, and habitat restoration at Dutch Slough could significantly improve conditions for many of these sensitive species. Big Break, the Marsh Creek delta, and lower Marsh Creek already harbor Sacramento splittail, Chinook salmon, Delta smelt, and other aquatic species for which the Dutch Slough site will be restored. Dutch Slough may also be an excellent opportunity to restore waterfowl habitat. One distinct sub-habitat that may provide substantial habitat value for waterfowl without undue artificial engineering of the marsh (e.g. water control structures and diked marsh) may be shallow, large ponds along the terrestrial edges of the site, where spring high tides and runoff may form brackish seasonal or perennial ponds. Native submerged aquatic vegetation that thrives in open water and ponds (especially pondweeds, Potamogeton spp.) would provide valuable foraging opportunities for waterfowl (Baye 2004). Indeed, the diversity of birds and other animals along the Big Break shoreline, in Marsh Creek, and upstream suggest that many other CALFED priority species will use the restored Dutch Slough site. Over 150 native species have been observed (Glover, pers com; Orlof 2000), of which 18 are CALFED priority species (r - Bank Swallow, Black Rail, Sandhill Crane, Swainson's Hawk, Yellow Warbler; m - Black Tern, Black-Crowned Night-Heron, California Gull, Common Yellowthroat, Cooper's Hawk, Great Blue Heron, Great Egret, Northern Harrier, Snowy Egret, White-Faced Ibis, White-Tailed Kite, Yellow-Breasted Chat, Western Pond Turtle). A recent survey of lower Marsh Creek by a DWR biologist confirmed a western pond turtle population of approximately 15-20 individuals (Hamilton, pers com, 2001). East Bay Regional Park District scientists and USFWS experts believe the area also supports giant garter snakes (Bobzien pers. com. 2001). In addition to providing valuable habitat for important faunal species, the Dutch Slough project could also provide an opportunity to restore rare, riparian plant communities that were once more common in the Delta but are now extinct or nearly extinct. Dr. Baye suggested that the existing levees would provide a suitable opportunity for creating stands of the willow-ladyfern community. The sand mound riparian woodland is another rare plant community that could be restored on the site, perhaps on the sand deposits in the middle of the Burroughs parcel.
Socio-Economic & Community Outcomes Achieved
Economic vitality and local livelihoods:
The Dutch Slough site will provide an opportunity for people to access the Delta shoreline and learn about the process of wetland restoration. The popular Marsh Creek Regional Trail, which extends from Antioch Pier to the City of Brentwood, already traverses the southwestern boundary of the site. More trails are planned, and the project team is developing a public access master plan to define the exact location and configuration of the trail network. The conceptual trail plan negotiated with the City of Oakley assumes that the trails will be largely confined to the top of the levees and the southern edge of the site near the base of the Contra Costa Canal; however, this conceptual plan may be revised during development of the public access master plan. As currently conceived, the trail system will circumnavigate the Emerson parcel along the existing levee road. The road will eventually be paved to accommodate emergency vehicles and policing. Wildlife viewing platforms and small-scale fishing piers may be developed along the trail to sufficiently provide for and direct public access. The interior of the Emerson parcels will be open to canoe and kayak access along a prescribed water trail. Facilities will also be constructed for a combination of active and passive recreation, including sports fields, interpretive and educational centers, and a swimming lagoon on the 55-acre community park site just south of the actual restoration site. In the short term, project partners are planning site tours, canoe trips and other activities to give people (especially Oakley residents) an opportunity to visit the area before it is officially open to the public.
Key Lessons Learned
The Dutch Slough project provides a significant opportunity to improve understanding of restoration science in the Delta ecosystem. Adaptive management employs the scientific method to maximize the information value of restoration and management actions. With the assistance of a panel of scientists, the project team will design restoration actions to test hypotheses about how the ecosystem functions and how best to achieve the project objectives. In this respect, adaptive management interventions are conducted as experiments. Project implementation will be guided by the best available information but will be monitored and implemented with the goal of increasing our understanding about the science of restoration.
Project partners realize the restoration must be planned and implemented carefully to avoid any unintended negative impacts. The project team is therefore committed to implementing the project in accordance with the following:
– Avoid and/or mitigate degradation of drinking water quality
– Minimize the potential for mercury methylation
– Measure and monitor water quality impacts
– Minimize the establishment of nuisance species through design and management (Project partners are working closely with the Contra Costa Mosquito and Vector Control District (CCMVCD) to design the project in a way that limits mosquito growth and West Nile virus.)
– Avoid and/or mitigate impacts to existing infrastructure and easements on and immediately adjacent to the property
Sources and Amounts of Funding
In the fall of 2002, the California Bay Delta Authority’s Ecosystem Restoration Program and the State Coastal Conservancy’s San Francisco Bay Area Program awarded $30 million in grants to fund the acquisition of the Dutch Slough project site and begin project planning.
Dutch Slough Wetland Restoration Project