Wildcat Creek, California
Considerations for Using Ecological Restoration: Combining Flood Control and Ecological Restoration
North Richmond is in Contra Costa County about 14 miles northeast of San Francisco on San Pablo Bay. This unincorporated community was first established during World War II, when laborers who came to work in the growing shipbuilding industry settled on the flood plains of Wildcat and San Pablo Creeks. The location exposed North Richmond to routine flooding during the wet winter months.
Flooding in the 1940s and 1950s prompted the Contra Costa County Flood Control District to seek assistance for flood control, beginning a decades-long search for flood control alternatives which eventually resulted in the choice of ecological restoration. A 1960 U.S. Army Corps of Engineers (COE) flood control feasibility study suggested several alternatives, but none were considered economically feasible. In 1971, the U.S. Department of Housing and Urban Development developed an urban renewal plan for North Richmond under its Model Cities Program. The plan emphasized recreational opportunities along Wildcat and San Pablo Creeks and the San Pablo Bay shoreline, proposed the creeks as focal points for redevelopment, and spurred COE to conduct another flood control study. This COE study focused on the multiple objectives of the Model Cities Plan, incorporating social well-being, environmental quality, and economic redevelopment as project benefits. It recommended traditional flood control measures, such as concrete box culverts and channels, but also proposed fresh water ponds and an earthen trapezoidal channel and landscaping on lower Wildcat Creek. Congress authorized the project in 1976, but the community was unable to raise its required share of the costs and the project was not carried out.
In 1980, the Contra Costa County Board of Supervisors proposed a bare-bones structural flood control project with no environmental amenities. Presented to North Richmond as the only affordable alternative, the "Selected Plan" was not well received. In response, members of several community groups formed a coalition to develop an alternative flood control plan that recognized the value of Wildcat and San Pablo creeks. The coalition wanted to
- preserve and enhance Wildcat Creek's riparian habitat, one of the last remaining streams in the San Francisco Bay area with continuous riparian habitat along its length;
- reduce sediment loads, since sedimentation could damage wetlands, reduce channel capacity (and thus flood protection), creating costly maintenance requirements; and
- provide for recreation and open space. The "Modified Plan" that was developed for Wildcat Creek by the coalition proposed modifying existing creek channels to simulate the natural hydraulic shape and processes of undisturbed streams, including features to deposit sediment in the upstream flood plain and to restore riparian vegetation. Regional trails and park facilities were also included.
In 1985, the County Board of Supervisors approved the Selected Plan, but left open the option to construct a multi-objective project if funding were to become available. Shortly thereafter, the U.S. Fish and Wildlife Service and the San Francisco Bay Conservation and Development Commission denied the permit applications for the Selected Plan because of concerns about possible impacts to wetlands and endangered species. Both agencies supported the Modified Plan as an alternative. A project design team was established to develop a consensus plan that would be environmentally sensitive but capable of conveying flows for the 100-year flood. Such a plan would address the concerns of both the general public and government agencies with regulatory authority over the project. The team met regularly for three years.
Stressors of Concern
Many of the stressors of concern in Wildcat Creek share a common point of origin. Development in the watershed has dramatically impacted the hydrological runoff characteristics. Intense storm flows had scoured the channel and caused extensive streambank destabilization and erosion. The flooding that resulted from the more rapid pattern had led to a management program of channelization and mowing of the riparian vegetation. Therefore, any restoration plan would need to address the amended hydrological regime which exists in the Wildcat Creek drainage area.
The Goals for Restoration
Wildcat Creek should safely convey 100-year flood flows past North Richmond using as much of the creek's natural character as possible. Restoration efforts should ensure such stressors as excessive sediment, high flows, elevated temperatures, and a damaged riparian zone be properly managed so they do not impair ecosystem functioning.
Restoring Stream Geomorphology: Choosing a Natural Channel DesignThe Consensus Plan modeled the channels according to natural channel geometry, rather than as hydraulic flumes. This allowed the project to remain within the narrow 180-foot right-of-way width specified by the Selected Plan, even with riparian vegetation along the channels, and provide the same level of flood protection as the Selected Plan.
A meandering or sinuous channel pattern more realistically reflects the stream channels in natural, undisturbed streams, and also reflects the original channel configuration that most likely existed prior to development. In natural systems, the degree of stream meandering depends largely on the channel gradient, with sinuous channels generally being associated with high gradient (greater than one percent) and meandering channels associated with lower gradients (less than one percent). The lower reaches of Wildcat Creek are lower gradient, and therefore naturally a meandering system. The natural channel design includes pools, riffles, and glides, which provide very different aquatic habitats.Restoration techniques based on interpretation and control of stream geomorphology take into account dynamics of sediment transport, as well as flow, throughout the entire watershed. A key component of the plan was to transport sediment past vulnerable marsh areas, where its deposition would be harmful, and deposit it along the flood plain and in the Bay, where the impact of its deposition would be minimal. The Consensus Plan featured a 10- to 15-foot wide meandering low-flow channel designed to carry the creek's mean flows; to scour and transport sediment in suspension at higher flow velocities; and to allow higher flows to spread onto the flood plains, lose velocity, and deposit sediment. In addition, a detention basin was placed upstream to trap sediments.
Riparian Tree RestorationA well-developed riparian corridor more closely reflects the natural habitat values of undisturbed streams. The Consensus Plan proposed planting trees along the low flow channels to guide channel formation and to shade the streams to prevent them from clogging with rushes, weeds, and sediment. Cuttings from nearby plants, seeds from native species, and some container stock were used as plantings along the stream.
Besides shading stream channels to prevent the growth of unwanted vegetation, a restored riparian zone can benefit aquatic habitats in many ways, including:
- roots of trees, grasses, and shrubs stabilize the stream bank by binding soil particles and providing resistance to the erosive forces of flowing water;
- stems and leaves of riparian vegetation provide shade that lowers water temperatures;
- leaves, stems, cones, fruit, and other plant parts that fall into the stream provide food for microbes, insects, and fish; and
- large woody debris that falls into a stream provides for the formation of pools and other habitat types.
The riparian sites were prepared by mowing and clearing the area where plantings would occur. Holes were dug for the plants, backfilled with existing soil with slow release fertilizer tablets, and covered with a layer of mulch. An automatic bubbler irrigation system was installed to allow vegetation to become established.
Initially, the use of chemical herbicides was prohibited, but competition from uncontrolled weed growth led to a low survival rate of the plantings. In addition, the weeds provided food for an enlarged pocket gopher population, which stressed the installed plants further. The project sponsors therefore recommended the initial use of chemical herbicides to reduce competition from opportunistic weeds.
An innovative vegetation maintenance plan was designed to keep the low flow channels free of vegetation until a riparian canopy could develop and shade out the unwanted, clogging reed growth expected in exposed, low-flow channels. Because the natural channel was designed to allow for a certain amount of sediment deposition, maintenance requirements were based on actual needs rather than annual schedules, reducing costs and environmental impacts.
Protecting Vegetative Cover throughout the Watershed
Implementation of this multi-objective flood control project aroused interest in the relationship between land uses, habitat, and water quality throughout the entire watershed. In contrast to the lower Wildcat Creek watershed, much of the upper watershed is undeveloped, consisting of the Wildcat Canyon Regional Park which owned and operated by the EBRPD. This park is used for grazing, recreation, open space, and vegetation and wildlife habitat.
While grazing can have positive effects such as preservation of open grassland habitat, fire protection, and food production, there can also be adverse impacts from over-grazing such as the loss of vegetation and erosion of disturbed areas and subsequent damage to wetlands and creeks from sedimentation. Therefore, the Wildcat Creek Grazing Management Demonstration Project was jointly designed and implemented by the EBRPD, the Contra Costa Resource Conservation District, a private rancher, and the University of California-Berkeley. The project was made possible by funding from the U.S. EPA through the San Francisco Estuary Project.
This project is intended to manage grazing activities over a portion of the 2,000 acre park. The specific objectives are to:
- rotate grazing to promote the growth of native perennial grasses and improve forage production;
- monitor plant species diversity and growth;
- protect riparian and wetland habitats;
- reduce soil erosion; and
- provide information about grazing management to ranchers, public land managers, environmental groups, and the general public.
Issues of Cost
By adding the objectives of public access and education, restoration of riparian habitat, and enhancement of aesthetic values to the original mission of flood control, a number of alternative sources of funding were available to implement the Consensus Plan that would not otherwise be available for single-purpose flood control projects. Table 6-7 lists contributors to the Consensus Plan.
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