Bolinas Lagoon Watershed
Stinson Beach Draft Watershed Workplan
The Board of Supervisors authorized the Department of Public Works to begin implementation of a County-wide Watershed Program on May 13, 2008. The purpose of the County-wide Watershed Program is to provide a framework to integrate flood protection and environmental restoration with public and private partners to protect and enhance Marin County’s watersheds. A watershed program was recommended for Stinson Beach to develop a suite of integrated projects that address on-going flooding and sedimentation issues in the lower sections of the creek while maintaining and improving habitat for steelhead trout and Coho salmon.
Easkoot Creek drains an area of approximately 1.59 square miles of mostly undeveloped and steeply forested watershed on the side of Mt. Tam. Early maps depicting the proposed subdivision development in the 1900s show the creek channel close to its present alignment until just downstream of the sharp turn at Arenal Avenue. The historic channel then branches off as the channel slope loses its grade and enters a willow thicket (on the current Park Service land). Early maps show an alternative alignment for Easkoot Creek breaching the sand dunes. With the development of Stinson Beach and the public park, Easkoot Creek has been maintained in its current alignment to Bolinas Lagoon.
There are three sources of flooding in Stinson Beach: overflow of Easkoot Creek, extremely high tides, and extremely high surf. Each of these alone can cause some flooding and when combined, can cause substantial flooding, property damage and public safety problems. The Arroyo and Calle area of Stinson beach are flooded annually during extreme high tide events.
Initially, when Flood Control Zone 5 was established one of the primary maintenance tasks performed was periodic dredging of the creek. Over time it has become evident that during medium to large storm events an active slide on Mt. Tam releases enough hillside material to fill in the creek, even if it has recently been dredged.
The essentially flat reach from Arenal to Bolinas Lagoon creates a slower moving creek and a natural area for sediment to settle and deposit. The excessive sediment build-up within this reach of Easkoot Creek has significantly reduced the level of flood protection through the Calle area of Stinson Beach. The private bridges along the residential streets known collectively as the “Calles” have limited to no clearance from the creek during storms, which may contribute to the flooding of neighboring homes and preclude access to and from Shoreline Highway. These bridges are a hydraulic constraint, but they are the primary access to homes and the primary access for emergency vehicles. The County and Flood Control Zone 5 has spent significant funds to perform limited dredging at the Calle bridges that is typically effective for only one to two seasons and requires dewatering the channel and relocating Steelhead trout to minimize impacts. As a condition of the sediment removal permit, the regulatory agencies have required that we investigate alternatives to the dewatering and the spot dredging approach since the creek has an established run of Steelhead. Staff are working with the National Park Service to explore the feasibility of constructing an interim sediment basin on Park Service property downstream of Arenal Avenue to capture sediment in one location instead of multiple locations downstream thus reducing impacts to Steelhead and other aquatic life
Stakeholders working through the Technical Work Group have identified issues and alternatives that were included in the development of the watershed study request for proposals.
The County solicited proposals and in October 2011 and awarded a contract to O’Connor Environmental Inc. (OEI) to conduct a hydrology and hydraulics (H&H) study and alternatives analysis to meet a suite of project goals. This study will focus on riverine flooding and also includes the identification of alternatives that would reduce ongoing maintenance costs and impacts from channel dredging while promoting alternatives that would enhance habitat and improve resiliency to sea level rise.
- A process to evaluate and prioritize feasible flood protection projects at the watershed scale
- Assessment of wetland and floodplain restoration opportunities along Easkoot Creek
- Identify integrated flood management and habitat restoration projects
- Identify opportunities to leverage local funding with State and Federal funds
- Evaluate flows utilizing projected rise in sea level within Bolinas Lagoon
Stakeholder and Community Outreach
The watershed program utilizes a collaborative, iterative process to develop integrated solutions to flood protection and habitat restoration. The Marin County Board of Supervisors recommended establishing stakeholder committees at three levels to support community outreach and to provide overall program direction (a complete list of committee members is attached at end of this document). A broad community outreach program is also recommended.
Description of Watershed Stakeholder Committees
Policy Advisory Committee - This group of elected officials is comprised of the District County Supervisor and two representatives from the Flood Control Zone 5 Advisory Board. This committee provides policy input on program direction and community issues and will meet 1-2 times per year.
Operations and Finance Committee- The Marin County Public Works director will use these meetings with Flood Control staff to evaluate progress and prioritize funding strategies and will meet 1-2 times per year.
Technical Work Group- This group includes staff of participating State, Federal and local regulatory and participating agencies and community members with a science and technical background who will be responsible for the review of watershed products and provide input on issues, needs and watershed priorities. This group will include conservation and watershed groups, homeowners associations and other technical experts within their respective watersheds. This group has met five times over the last year to scope the RPF and to provide input and to review the development of work products
Targeted community meetings, presentations at various local boards and homeowners associations and utilization of the watershed program website (www.marinwatersheds.org) will support communication to the community at large. The program website provides dedicated information about the watershed and is regularly updated with meeting notices, proposals and projects.
Program Description and Outcomes
The watershed program will build upon existing studies and develop new analytical tools to evaluate and quantify the extent of flooding and to evaluate the range of proposed solutions. The study and tools developed will provide staff and the community with an understanding of existing conditions as well as understanding how various alternatives could reduce flood damage and restore creek habitat.
The following is a description of the proposed tools and outcomes. An overview of existing conditions and relevant studies is available at www.marinwatersheds.org
Hydrology and hydraulics study:
The hydrology and hydraulics study will perform the following main tasks:
- Quantify and communicate the existing creek and floodplain conditions in Easkoot Creek.
- Develop a watershed hydrology model to identify a set of flood flows including limited geomorphic work to improve understanding of sediment transport and deposition and to assess the rate of sediment deposition.
- Develop a hydraulics model of Easkoot Creek and model conceptual project alternatives for their benefits (including evaluation of sea-level rise scenarios) with input from our stakeholders
- A coastal geomorphologist (John Largier-part of the OEI team) will evaluate the potential issues involving a direct ocean connection for the creek. In particular, potential outlet stability issues and the implications of summer closure of the bypass channel will be evaluated with respect to impacts to water quality, fisheries, flooding, and facilities at Stinson Beach.
Evaluation of Coastal Flooding and Erosion
While the primary focus of this program is to identify projects to protect the community from riverine flooding, Stinson is also impacted by coastal flooding and erosion. Direct coastal flooding is currently being studied by the USGS/NOAA under the “Our Coast, Our Future” project. Once the riverine flood studies are complete, County staff will work with USGS and NOAA staff to evaluate the combined risk from coastal and riverine flooding and to evaluate alternatives that address impacts from both types of flooding.
Develop preliminary (appraisal-level) designs for potential flood mitigation solutions that are protective of creek habitat and integrated at a watershed level. At a minimum, details for each evaluated project should include:
- Description, including associated facilities, their proposed function, operational and maintenance requirements, and short- and long-term sustainability
- General location, dimensions, and extents, with elevations of key components where appropriate (e.g., weir(s), detention pond)
- Approximate construction, operation, and maintenance costs
- Assessment of current vegetation and sediment removal maintenance methods
- A list of assumptions and the type of data used to establish these for design development
This process and study results will be summarized in a final report. The final report will also include recommendations for leveraging local funds to secure State and Federal grant funds and describe the type of local revenue measures that could support project implementation.
November: Consultant begins work on the Stinson Beach Watershed H&H Study
Technical Working Group meeting #4 to introduce the consultant team
December Field surveys
January: Consultant team reviewing data to produce hydrology and hydraulics model.
February: Policy Advisory Committee meeting
March: Technical Working Group meeting to prepare for Community Meeting and discuss criteria development
April: Community Meeting to present overview of existing conditions and the H&H model
July: Technical Working Group meeting #5 to continue development of alternatives.
Policy Advisory Committee meeting
August: Technical Working Group meeting #7 to prepare for Community Meeting
September: Draft Report from consultant
October: Community Meeting #2 to present study results (including alternatives) and to discuss next steps
November: Final Report from consultant
NOAA and FEMA coastal mapping to be released
Easkoot Creek Hydrology and Alternative Process
Coastal Flooding mapping and assessment
Staff Plate and Streamflow Monitoring
GIS and Habitat Mapping
County of Marin
Flood Control Zone 5
Liz Lewis, Principal Planner
- Manage overall schedule, deliverables development, program budget, and communication with partners
- Provide input and review of WMP technical memorandums and other deliverables
Roger Leventhal, P.E. Associate Engineer
- Manage the Watershed Master Plan (WMP) study process
- Draft the WMP and manage development of related maps and graphics
- Update hydrology and hydraulics models for Coyote Creek and Arroyo Corte Madera del Presidio
- Develop hydrology and hydraulics calculations and models for the remaining sub-watersheds in Richardson Bay as-needed
- Provide briefings and updates to partners and local jurisdictions
- Coordinate review of draft documents with management, counsel, and stakeholders and facilitate discussion in technical work group meetings
- Manage and review consultant products related to development of the WMP technical memorandums and other deliverables
Neal Conatser, Assistant Engineer
- Initiate pilot asset management pilot effort
- Develop financial strategy to support project implementation
- Provide input and review of WMP technical memorandums and other deliverables
Chris Choo, Senior Planner
- Coordinate outreach and meetings with the Technical Working Group
- Manage EPA grant reports and deliverables
- Provide input and review of WMP technical memorandums and other deliverables
- Conduct habitat assessments and support data analysis
Laurie Williams, Senior Planner
- Develop GIS database to support restoration project planning and prioritization
- Prepare maps for website and stakeholder meetings
- Support asset management pilot project
Rob Carson, Planner
- Support the tasks funded through the EPA grant for Richardson Bay and develop and manage the Quality Assurance Protection Plan and Monitoring Plan for precipitation monitoring
Beginning in the 19th century, dairy ranches were established in Rancho Las Baulines. Initially accessible only by boat or horseback, the watershed became more populated after the first road, built in 1870, connected the area to Sausalito.
The community now known as Stinson Beach, located at the base of the western slope of Mt. Tamalpais, was originally populated by tent camps. Later, a subdivision known as “Stinson Ranch” was developed and the first water system in the area was established to serve the subdivision. Following the 1906 San Francisco earthquake, the area experienced an influx of residents and businesses. Use of the area by tourists began in the early 20th century with day use at a County Park located on the beach.
Changes to Watershed Processes
For over thirty years, local community groups and scientists have brought attention to the ecological value of the lagoon and the need to slow sediment deposition to preserve it. The Bolinas Technical Advisory Committee was appointed by the County Board of Supervisors in 1974, and the Committee to Save Bolinas Lagoon was established in 1994 by the Bolinas Lagoon Foundation. Working with local experts, the Committee to Save Bolinas Lagoon secured funds from Congress for initial studies for restoring the lagoon. MCOSD developed a management plan to address the loss of tidal and subtidal habitat and sedimentation in Bolinas Lagoon in 1981, and revised the plan in 1996.
In 2008, the Bolinas Lagoon Ecosystem Restoration Project: Recommendations for Restoration and Management was completed by a working group of community representatives and scientists, coordinated by the Gulf of the Farallones National Marine Sanctuary Advisory Council, with support from MOSD and USACE. Restoration objectives and recommended actions include restoring natural sediment transport and ecological functions of the lagoon, identifying and managing non-native species, and protecting water quality.
Each of these restoration objectives are complemented by a set of management recommendations that include implementing best management practices throughout the watershed, removing fallen trees from the lagoon, establishing a public education program to reduce human disturbance of harbor seals, immediately removing introduced cordgrass found in the Lagoon, and developing emergency response plans to address the closure of the lagoon inlet or an oil spill.
Historic land use activities that could and may still be contributing to the sedimentation problem in the lagoon are addressed in the Historical Perspective of Bolinas Lagoon Watershed (Van Kirk 2002 1). The Bolinas Lagoon Watershed Study: Input Sediment Budget (Tetra Tech 2001 2) evaluates “the sources and magnitude of sediment delivered to the lagoon via erosional processes within the watershed.” This study concluded that current erosion rates are near background (pre-1850) levels within the watershed.
Easkoot Creek originates in the steep, west-facing slopes of Bolinas Ridge. The three tributaries; Fitzhenry, Laurel, and Black Rock Creeks join to form Easkoot Creek just upstream of Shoreline Highway in Stinson Beach. After exiting the uplands, the Creek turns northwest and flows behind the coastal dune until it enters the south arm of Bolinas Lagoon. It has been debated whether or not the creek historically flowed to the Lagoon or went straight out to the ocean. Recent research indicates that the current channel location very closely matches its historic location, and that only during high flow events would the creek change its course and flow directly to the ocean across the beach (Van Kirk 2002, Tetra Tech 2001).
Nearly 170 meters of Easkoot Creek through the town of Stinson Beach has riprap, SacCrete, gabions, or retaining walls stabilizing its banks (Fong 2002 3). Over the years levees had been built up along lower Easkoot Creek, adjacent to Stinson Beach Park, with spoils from sediment dredging activities. These artificial levees restricted hydrologic connectivity of the stream to its floodplains and adjacent wetlands. This reach of creek also exhibited markedly low amounts of large wood and no viable pools (Fong 2002).
The lower reach of Easkoot Creek flows through a tidal marsh located between Shoreline Hwy and Calle del Arroyo. With the start of construction of the Seadrift lagoon and subdivision in 1960, and the presence of the delta at the mouth of Stinson Gulch, tidal circulation to the southeastern arm of Bolinas Lagoon was restricted. Removal of the Stinson Gulch delta constriction and the restoration of a more natural tidal range allowed the marsh at the mouth of Easkoot Creek to nearly double in size between 1968 and 1998 (PWA 2006 4).
The steep slopes of the upper Easkoot watershed are prone to landslides. Sediment derived from the hillslopes is transported to the low gradient and tidally influenced reaches where it is stored in the channel. In order to maintain channel capacity, the National Park Service has had to remove sediment from the creek at Stinson Beach Park on a regular basis.
Bolinas Lagoon represents a unique habitat within the watershed, consisting of mudflats, marshes, tidal channels, and a flood shoal island. The primary vegetation communities within the watershed are coastal scrub, Douglas fir and redwood forest, and grasslands. There are small patches of eucalyptus, oak and oak-bay woodlands, riparian scrub woodland, and pine cypress forest.
Easkoot Creek is located within one of the most biologically diverse and ecologically significant areas on the California coast. The watershed supports a mix of upland and aquatic habitats. It borders state and federal parks, private property, and local municipality lands. Upland habitats are dominated by coast redwood and Douglas fir forest along the inner gorges, chaparral on the convex slopes, and grasslands with a strong native component (NPS 2003 5). However, the riparian plant community along Easkoot Creek contains the largest number of non-native plants when compared with other east-side tributaries (Fong 2002). Only isolated remnants of historic willow and alder forest remain. The Easkoot Creek watershed is within the Pacific Flyway, “the major corridor for movement of migratory shorebirds, raptors, and other birds along the West Coast of North America” (NPS 2003).
A complex of habitats supports a variety of species at the mouth of Easkoot Creek at Bolinas. The finger of lagoon that extends to the mouth of Easkoot Creek, commonly referred to as south arm, supports saltmarsh habitat, frequently exposed mudflats, and subtidal channels, all bordered by development on the Stinson Beach Spit. In recent years, saltmarsh habitat has been expanding in the south arm due to the restoration of a more natural tidal range following the removal of the constriction caused by the Stinson Gulch delta (PWA 2006). This area serves as a nursery for fish, harbor seals haul out on the mudflats, rails are present, and an abundance of invertebrates provide a food source for shore and waterbirds (PWA 2006 6).
Easkoot Creek drains into the east side of Bolinas Lagoon and is the second largest drainage in the watershed. Several small tributaries (e.g., Fitzhenry, Laurel, and Black Rock Creeks) drain the upper watershed. Much of the upper watershed is publicly owned and supports a mix of forested, chaparral, and grassland habitats. The lower watershed is mostly privately owned and more heavily developed. It is tidally influenced with saltmarsh forming the transition zone between mainstem Easkoot Creek and Bolinas Lagoon.
Fish and Wildlife
The watershed supports a number of special-status plants and animals. Of particular interest are the occurrences of species found in coastal marsh and scrub along the Bolinas Lagoon Spit and in the vicinity of Stinson Beach.
Noteworthy species in Bolinas Lagoon include clapper and black rails, salt marsh common yellowthroat, great egrets, and great blue herons occur around the lagoon, and California red-legged frog are known to occur adjacent to the lagoon in freshwater ponds. The 1996 Bolinas Lagoon Management Plan Update identifies additional special-status species found in the Bolinas Lagoon watershed, including California brown pelican, American peregrine falcon, Point Reyes mountain beaver, and Point Reyes jumping mouse.
In Pine Gulch Creek, species include Coho salmon, steelhead trout, northern spotted owl, salt marsh common yellowthroat, black swift, California red-legged frog, and Marin manzanita are known to occur. Since 1997, the National Park Service Coho Salmon and Steelhead Trout Restoration Program staff has been actively monitoring fish populations along 12 kilometers of mainstem Pine Gulch Creek. Coho salmon were documented within the watershed in 1968, but monitoring by NPS staff failed to document a single Coho salmon from the fall of 1997 to the summer of 2000. Since that time, Coho salmon have been documented annually by NPS staff in Pine Gulch Creek. Since 2001, the highest number of adult spawners were observed during the 2004-2005 year class in which three adults and three redds were observed. In 2007-2008, one Coho salmon and two redds were observed (NPS 2008 7).
California red-legged frog and steelhead trout are known to occur in Wilkins Gulch. Steelhead trout are known to occur in Morse’s Gulch, McKinnon Gulch and Stinson Gulch.
The Easkoot Creek subwatershed is known to support a remnant population of steelhead. According to Fong (2002), the historic distribution of steelhead within the watershed is roughly similar to their distribution today. However, the current population size does not reflect historic abundance. The subwatershed may support California red-legged frog, federally listed as threatened and Species of Special Concern; however, there are no documented occurrences. Red-legged frogs have been documented in a small brackish pond on the east side of Highway One in the north end of the lagoon.
Human Habitation and Land Use
Land Use Imperviousness
Much of the watershed is in public ownership. Private communities occur within the Pine Gulch Creek subwatershed, and some private parcels within Pine Gulch Creek are used for farming. Much of the Easkoot subwatershed is county, state, and federal parkland. The Golden Gate National Recreation Area, formed in 1972, acquired most of the open land surrounding the community of Stinson Beach. Other protected lands include Bolinas Lagoon and Mt. Tamalpais State Park.
Organic farmers along Pine Gulch Creek are working to establish a cooperative agreement with local agencies to protect Coho salmon and steelhead trout habitat in the creek, while also maintaining local agriculture. For more information, contact the Marin Resource Conservation District.
The watershed supports limited residential and commercial use. Commercial uses are generally geared toward serving the large summer tourist population. Stinson Beach residential use is at its peak in the summer, when single-family homes may be occupied by multiple families coming to the area for vacations. While the community of Stinson Beach remains small (fewer than 1,000 residents) and seasonal occupancy remains a typical community feature, full-time residential use is increasing (Stetson 2006 8).
1 Historical Perspective of Bolinas Bay (Lagoon)
2 Bolinas Lagoon Watershed Study Input Sediment Budget
3 D. Fong. Fisheries Assessment For Bolinas Lagoon Tributaries within the Golden Gate National Recreation Area, 1995-2000
4 Phillip Williams and Associates. Projecting the Future Evolution of Bolinas Lagoon - Final Public Draft.
5 National Park Service. Environmental Assessment: Easkoot Creek Restoration at Stinson Beach
6 Phillip Williams and Associates. Projecting the Future Evolution of Bolinas Lagoon - Final Public Draft
8 2005 Urban Water Management Plan