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Dutch Slough Tidal Restoration Project


Announcements

Project permits have been received and Phase 1 of 3 will begin construction in the spring of 2017. If you have questions about the project, email us at DEE@water.ca.gov or call (916) 651-0851.


Left: The Dutch Slough Tidal Restoration Project prior to construction (2016). Right: An example of restored tule marsh (Tule Marsh at Coyote Hills, http://www.calalive.org/node/109)


The Dutch Slough Tidal Marsh Restoration Project will soon become 1,178 acres of critically needed habitat for fish and wildlife in the Sacramento-San Joaquin Delta. Formerly slated for urban development, the project's location in the western Delta offers the opportunity, soil types, and lack of subsidence to create a large area of tidal marsh and complex intertidal channels favored by native Delta species. Shaded channels, native grasslands, and riparian forests will be restored in the upland portions of the site. Restoration of these habitats is considered a critical action to increase numbers of native sensitive species and improve general ecological health of the Delta. This project provide critical habitat for native plants, fish, and wildlife that are in rapid decline in the Delta.

The goals of the project are to:

  • Benefit native species by re-establishing natural ecological process and habitats
  • Contribute to scientific understanding of Delta habitat restoration
  • Provide shoreline access and educational and recreational opportunities

The project will provide outdoor recreation and educational opportunities for the residents of the Delta and Bay Area. The former landowners of the project area, once pursuing permits for developing the area with up to 6,000 houses, partnered with state, federal, and private agencies to create a project to provide an island of habitats and open space in the rapidly urbanizing area of eastern Contra Costa County. Fifty-five acres located in the south-central portion of the original land purchase will be deeded to the City of Oakley for a community park. To coordinate with the park, the Dutch Slough Project will include recreation features on the Emerson (westernmost) parcel, including bike/pedestrian trails, shoreline access, fishing opportunities, and interpretive signs to facilitate educational visits to the site by school and community groups.

Along with DWR, the following partners have undertaken the long process of scoping, planning, preparing environmental documents, and securing funding:

  • Department of Fish and Wildlife (CDFW)
  • State Coastal Conservancy (SCC)
  • Reclamation Districts 2137 and 799
  • California Bay-Delta Authority
  • Natural Heritage Institute (NHI)
  • City of Oakley
  • Ironhouse Sanitary District
  • Private consultants

The CALFED Ecosystem Restoration Program and SCC provided the funds to purchase the property and do the initial planning, including a conceptual restoration plan, feasibility study, and Draft Environmental Impact Report. The final planning and implementation will be paid for by DWR, SCC, CDFW, and the CALFED Program.

Timeline

  • In the fall of 2001, NHI and DWR identified the site as an important restoration opportunity and began working cooperatively with the landowners to obtain grant funding to acquire and restore the property.
  • During 2002, the project partners worked with the Oakley City Council to build local support for the project.
  • In 2002, CALFED's Ecosystem Restoration Program (now part of the Department of Fish and Wildlife) and SCC’s San Francisco Bay Area Program awarded grants to fund the acquisition.
  • In the fall of 2003, DWR completed the purchase of the restoration site.

The Dutch Slough site is located in the City of Oakley, eastern Contra Costa County, in the western Delta. The site encompasses 1,178-acres, and is bound by Dutch Slough on the north, Marsh Creek on the west, the Contra Costa Canal on the south, and Jersey Island Road on the east. The site comprises three parcels, partially separated by Emerson Slough and Little Dutch Slough. Unlike much of the Delta, the site is not deeply subsided and still has topographic diversity.

East Bay Regional Park District's Big Break Regional Shoreline is adjacent to the northwestern edge of the site, and the Marsh Creek Regional Trail runs along the southwest side. The City of Oakley will own a 55-acre community park at the south end of the restoration site. The restoration project will re-route Marsh Creek onto the Emerson (westernmost) parcel, and once the restoration is complete, the Marsh Creek Trail will continue to the new mouth of Marsh Creek.

The three parcels which make up the project site were originally leveed around the turn of the 20th century. For over a hundred years, the three parcels of the Dutch Slough property were used for grazing and dairy operations. During the past 30 years, eastern Contra Costa County has undergone a rapid urbanization, and, beginning in the 1990s, the former landowners began securing approvals for the eventual development of the property. In 1997, Contra Costa 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, this property was within the city limits, and the City accepted the County's development agreement.

1. What is a tidal marsh and why is tidal marsh restoration important?

Tidal marshes form on low-lying lands adjacent to coasts and estuaries. They are flooded and drained by the tides. Much of the historical Sacramento-San Joaquin Delta was tidal marsh, which was habitat for a rich diversity of wildlife including waterfowl, deer and elk, fish, and shellfish. Today, after over 150 years of human changes, it is widely accepted that the Delta ecosystem is in crisis. Restoration of some lands to tidal marsh and related aquatic and terrestrial habitats is widely regarded as necessary to improve the health of the Delta so that it can sustain both humans and wildlife.

2. Will the project harm drinking water in Contra Costa County?

The project is not expected to have any measurable impact on drinking water quality. One of the ecosystem benefits of the project is the addition of nutrients, including dissolved organic carbon (DOC), to the local aquatic habitats. DOC can react with disinfectants (like chlorine) at water treatment plants to form toxic chemicals called trihalomethanes. The closest drinking water intake, the Rock Slough intake to the Contra Costa Canal, is located approximately eight water miles from the project site, and it is expected that any DOC released from the project site would be diluted to negligible levels by the time it reaches the intake. DOC will be monitored both before and after project construction.

3. Will the project increase mercury levels in the Delta?

Mercury from the gold rush period and from modern day pollution is a problem throughout the Bay-Delta watershed. In certain wetland environments, mercury combines with hydrogen to form methyl mercury, a particularly harmful form of mercury. Methyl mercury can cause nervous system problems, especially in fetuses and children. People become exposed to methyl mercury when they eat fish containing high levels of it. Fortunately, fish in the Dutch Slough area have the lowest levels of methyl mercury in the Bay-Delta region, and several recent studies funded by the state of California indicate that tidal wetlands can reduce levels of methyl mercury in the environment. Mercury in the project area is currently being monitored, and DWR will continue to monitor methyl mercury levels after the project is completed. Meanwhile, DWR, along with other state and federal government are working to reduce methyl mercury in the Delta and limit human exposure to toxic levels of mercury.

4. Will the project increase mosquitos and West Nile Virus?

The project partners will work closely with the Contra Costa Mosquito and Vector Control District (CCMVCD) to design the project to limit mosquito growth and West Nile virus and will continue to work with CCMVCD after the site is restored. The goal of the CCMVCD program is to prevent mosquito problems before they happen.

The project partners realize that restoration must be planned and implemented carefully to avoid any unintended negative impacts. The project team is committed to implementing the project consistent with the following:

  • Avoid and/or mitigate degradation of drinking water quality
  • Minimize the potential for mercury methylation
  • Measure water quality impacts
  • Minimize the establishment of nuisance species through design and management
  • Avoid and/or mitigate impacts to existing infrastructure and easements on and immediately adjacent to the property

DWR and the SCC worked with other project partners to develop a restoration plan that would achieve the goals and objectives of the project. In addition to the project team, a Restoration Committee (PDF: 20 KB) and Adaptive Management Working Group were convened to assist in project planning. The Restoration Committee obtained input from and provided information to stakeholders and the public. The Dutch Slough Adaptive Management Working Group comprised nine scientists who identified key science questions, provided technical review, and helped develop the project's adaptive management plan. A consultant team, led by Philip Williams & Associates (now ESA PWA) was hired to help develop restoration alternatives and conduct a feasibility analysis of those alternatives.

The Coastal Conservancy and CALFED awarded grant funds to the City of Oakley to develop a public access master plan for the Dutch Slough Restoration Site and the adjacent community park site. The purpose of the master plan is to develop an overall vision for public access to the site. A Request for Proposals was issued in 2004, and 2M Associates was contracted with the City in March 2005, and the City Council approved the Dutch Slough Community Park and Public Access Conceptual Master Plan (PDF: 65.1 MB) in August 2006.

Year Activity
2003 Property acquisition
2003-2004 Initial design and development of alternative
2003-2005 Adaptive Management Working Group (AMWG) meetings
2005 Public Scoping
2005-ongoing Baseline monitoring
2006 Conceptual Plan and Feasibility Report
2008 Draft EIR
2010 Final EIR and development of Revised Conceptual Plan
2011 Develop final engineering drawings and grading plans, prepare permit documents, and local coordination
2012 Apply for all state and federal permit
2013 Being grading Emerson parcel
2014 Complete grading Emerson parcel
2015 Begin tule cultivation on Emerson
2015 Begin grading Gilbert parcel
2016 Breach Emerson Parcel. Complete grading Gilbert parcel
2017 Being tule cultivation on Gilbert
2018 Breach Gilbert parcel
*Schedule for Burroughs parcel restoration has not been established

Excavation & Import of Fill Material
The primary goal for the project is to create large expanses of intertidal tule and/or cattail marshes. These marshes develop in areas where the soil surface is exposed at low tide and flooded at high tide. Currently, the parcels slope downward from south to north, with southern elevations being about 6 feet above sea level, and the northern ends about 6 feet below sea level. To maximize the area that will become tidal marsh after the levees are breached, higher areas will be graded down and the excavated soil moved to areas of lower elevation to create a gradually sloping marsh plain that varies from about 2 feet above to 2 feet below sea level. In addition, about 500,000 cubic yards of soil will be imported and placed in lower elevation areas. Because the northern portions of the site are the most subsided, it is not economically feasible to import the large quantities of material necessary to bring these areas to marsh elevations. These areas will be restored or enhanced as other habitats—open tidal water, managed marsh, or uplands.

Grading
After the soil is placed in areas that will be restored to tidal marsh, it must be graded to the correct elevations and slope, and tidal channels excavated. Proper grading is necessary to allow tidal waters to move freely, transporting nutrients, sediments, plant material, invertebrate organisms, and small fishes into and out of the marshes.

Vegetation Pre-establishment
In tidal marshes, tules germinate best in areas where the soil surface is exposed part of each day and water depths rarely exceed 1 foot. Once established, however, tules can withstand deeper and longer flooding. Therefore, to increase the area of vegetated marsh, a one or two-year period of tule pre-establishment will occur prior to levee breaching. Water levels will be controlled in new marsh areas to facilitate growth of large expanses of tules and cattails. These tules will also prevent soil erosion when the site is breached.

Levee Breaching
Once the tules are growing well, the levees will be breached, Delta waters will enter the site and project construction will be complete.


DWR formally approved the Final Environmental Impact Report (EIR) on March 17, 2010. The Notice of Determination and Final EIR for the restoration and public access portion of the project is available for review at the California State Clearinghouse.

EIR

Draft Environmental Impact Report: Dutch Slough Tidal Marsh Restoration Project, November 2008

Dutch Slough Tidal Marsh Restoration Conceptual Plan and Feasibility Report

Marsh Creek Watershed