Richardson Bay Watershed

Richardson Bay

Draft Watershed Workplan


The Southern Marin Watershed Program is a collaborative effort of the City of Mill Valley, the County of Marin, and Flood Control Zones 3 and 4. The purpose of the 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 and to identify solutions that will enhance and protect the diverse habitat of the lands that drain into Richardson Bay. The Board of Supervisors authorized the Marin County Department of Public Works to begin implementation of a county-wide Watershed Program on May 13, 2008.

This document summarizes the content and scope of the Southern Marin Watershed Program.

Numerous studies were produced over the decades to identify and guide the construction of projects to reduce flood damage in the southern Marin watersheds that drain to Richardson Bay. A primary task for the Southern Marin Watershed Program will be to develop a Watershed Master Plan (WMP) that integrates flood protection needs with opportunities for creek and water quality enhancements.

The WMP will identify opportunities that provide the following benefits:

  • Develop cost effective solutions to help reduce flooding
  • Protect, enhance, and restore sensitive creek and wetland habitat and water quality
  • Identify multi-benefit projects that will improve the ability to compete for state and federal funding
  • Identify the impacts of sea level rise and develop project concepts that could be adapted to rising tides
  • Evaluate the beneficial re-use of dredged sediment from Coyote Creek and other sediment removal projects for wetland restoration, levee maintenance, and shoreline protection
  • Improve efficiency of existing flood maintenance operations

The purpose of the WMP is to provide a comprehensive road map for future project implementation. This summary describes the scope and budget for development of the WMP and the stakeholder process that will be implemented to support this work.


The low lying areas bordering Richardson Bay have experienced periodic flooding for decades. The County Board of Supervisors formed both Flood Control Zone 3 and Zone 4 during the late 1950s to address the flooding experienced along the low-lying areas bordering Richardson Bay. The WMP study area addresses 14 square miles draining to Richardson Bay including the sub-watersheds of Arroyo Corte Madera del Presidio, Coyote Creek, Ryan Creek, Sutton Manor Creek, and East and West Creeks.
Numerous facilities and channels have been constructed to address flooding including eight (8) stormwater pump stations, an earthen and concrete levee system, and several drainage improvements. In addition, sediment removal is regularly implemented as well as annual vegetation maintenance activities. The Marin County Flood Control and Water Conservation District also maintains two stream gauges, a weather station, and holds numerous easements and properties in order to maintain these channels and structures.
The City of Mill Valley evaluated opportunities to increase the level of flood protection within the Arroyo Corte Madera del Presidio watershed in response to the 2005/06 floods. Based on these studies, over $70 million dollars in flood control projects have been identified for planning and implementation. This process will help the City and residents to evaluate these recommendations so that alternatives can be prioritized.

An overview of existing conditions and relevant studies is available at

EPA Grant

In 2010 the County received nearly $370,000 in grant funds from the EPA’s 2010 San Francisco Bay Water Quality Improvement Fund for improvements to the Richardson Bay watershed. Richardson Bay has been listed as being impaired by pathogens related to measured high levels of coliform bacteria. The EPA funds will be used to reduce the potential for coliform bacteria to reach Richardson Bay. Funding will include work to restore creek-side vegetation along a tributary to Warner Creek in Boyle Park to increase filtration with native vegetation and to conduct outreach in the community. Funding will also support the Richardson’s Bay Regional Agency’s efforts to develop a houseboat and marina monitoring plan.

Program Description and Outcomes

The Southern Marin Watershed Program will build upon the decades of existing operations and improvements. A suite of analytical tools will be used to identify and prioritize a range of flood protection alternatives that integrate habitat restoration benefits. These analytical tools and the process for developing and evaluating the proposed project alternatives will be summarized in the WMP.

The WMP will also include recommendations for how to fund the proposed work, including a discussion of local revenue measure options and describe opportunities to leverage local funds to attract state and federal grant funds.

The District has identified the general causes of flooding within the watershed and a general description of flooding will be included in the WMP.

A description of the individual tools and methods to be used are described below.  

Hydrology and Hydraulics Models

An understanding of how much water is moving through the watershed (hydrology), how fast it is moving, and where it is going (hydraulics) is critical to quantifying flooding impacts and identifying solutions. The development and use of computer models to quantify stormwater runoff and channel flow are the industry standard for describing flooding and analyzing proposed solutions. These modeling tools will allow us to identify areas that need increased flood protection and to understand how channel and floodplain modifications will influence the ability of the channel to carry flood flows. Utilizing existing flow models or developing new ones will provide the ability to refine the engineering analysis required to develop conceptual design alternatives and to get a better idea of the costs associated with implementation

The watershed based hydrology and hydraulics models will allow staff and the Technical Working Group to review conceptual project alternatives for their benefits including an evaluation of sea level rise scenarios.

Climate Change Adaptation Scenarios

The Richardson Bay watershed is one of the most highly susceptible areas of Marin County to the impacts of climate change. Rising tide levels in San Francisco Bay will result in more direct wind-wave shoreline erosion (wave energy increases as the square of water depth) as well as increased river flooding as the stormdrain system is unable to drain against the tidal backwater. Short duration rainfall intensities are anticipated to increase and will exacerbate stormwater flooding as well as landslides and soil erosion in the upper watershed.  

The Master Plan will begin the process of organizing and planning for climate change in the watershed. The WMP will include a synthesis of the range of projections for Bay sea level rise and an evaluation of the potential impacts on existing and proposed flood protection projects. The WMP will consider a range of potential adaptation strategies, for example:

  • Higher, larger levees
  • Outboard habitat transition zone levees
  • Buffer zones and beaches
  • Detention basins
  • Raising and floodproofing structures
  • More pump stations
  • Planned retreat


The WMP will provide the technical studies that allow community decision makers to frame their planning decisions on where to devote financial resources over the next thirty to one-hundred years.

Alternatives Analysis

One of the primary goals of the Watershed Program is to identify cost effective alternatives for improving the level of flood protection. The hydrology and hydraulics models will be used where appropriate to evaluate the proposed alternatives in each watershed. Utilizing these tools, the District and the Technical Working Group will be able to evaluate a range of alternatives to identify practical and sustainable projects. The models will be used to analyze and develop the full range of feasible measures consistent with the program goals. Preliminary costs, flood protection benefits, and multi-benefit projects will be clearly identified through this process and in the WMP.

The watershed program considers the development of multi-benefit projects as a basic principle to ensure that the identified alternatives are eligible for the broadest range of funding at the state and federal levels.

A series of technical memorandums describing the design methodology and results of the various flow modeling efforts will form the foundation of the WMP. These memorandums will contain the engineering details for technical review by agencies, partners, and interested parties. Opportunities for increased flood protection, restoration, and habitat benefits will be identified and evaluated.

A set of flood protection and habitat restoration criteria would be developed to evaluate and prioritize the recommendations and to identify integrated projects. These criteria would also consider project feasibility, sequencing and existing flood protection objectives. The alternatives analysis would also include a thorough treatment of climate change and sea level rise issues. The WMP would include a general description and conceptual drawings to illustrate the proposed design alternatives.

GIS-based Mapping and Database Development

Staff will compile existing Geographic Information Systems or GIS data (publicly-owned parcels, stream data, locations of current and past restoration sites, and fisheries data) into a watershed-scale restoration opportunities database. The database will be used to analyze restoration needs and to support the identification of multi-benefit projects. The projects will be prioritized based on the GIS analyses and the modeling results and described in the WMP.

Financial Strategy

The goals of the financial strategy are to review budgetary needs for the operation and maintenance of existing assets and to define a strategy for annual funding of a reserve amount suitable to address long-term projected needs. Additionally, alternatives for funding recommended projects will also be described including different revenue measures, available reserves from existing funding sources, and potential grant opportunities, among others.

Watershed Master Plan

The Watershed Master Plan will provide a comprehensive, integrated strategy for flood protection and environmental restoration that will serve as a guiding document for the next thirty years. A thirty year time frame is recommended in light of the State of California predictions that San Francisco Bay is likely to experience a sea level rise of about 16 inches by 2050.

The Plan will describe the proposed alternatives, recommendations for project sequencing, and identify multi-benefit projects that both enhance flood protection and habitat. This type of integrated approach to flood and creek management is consistent with current state and federal grant guidance to identify projects that are multi-purpose and multi-benefit in nature.  

Staff is undertaking a systematic review of existing conditions. Prior work is being assessed and data gaps will be identified. The WMP will allow the District and partner agencies to answer the following questions:

  • Which previously defined improvements should be considered?
  • Are there improvements that have not yet been defined, but should be considered?
  • What information is needed before improvements can be designed?
  • How can District projects, both constructed and planned, effectively address the potential impacts posed by climate change and sea level rise?
  • Do the District’s monitors and gauges provide it with the data necessary to develop hydrology and hydraulics suitable for the design of its construction projects?
  • Are there projects which present opportunities for increased flood protection, fish passage, and/or riparian restoration?
  • Do current maintenance efforts ensure the effective operation and optimum use of existing facilities?
  • Where will the District or partner agencies need to pursue new easements or fee title acquisition to support future maintenance and project implementation?

This information and the supporting data will be summarized within the WMP. Consideration of sea level rise scenarios and future adaptation will be included in this effort. Engineering and technical work will be led by County staff with consultant assistance to supplement the existing hydrology and hydraulic analysis where needed.
The WMP will also include recommendations for leveraging local funds to attract state and federal grant funds and describe the type of local revenue measures that could support project implementation.

The major findings of the WMP will be published in a user-friendly web-based “booklet format” to effectively communicate findings and recommendations to partner agencies and the community. The goal is to summarize and communicate key findings and recommendations in a concise, graphics rich format.

Stakeholder Process

The WMP will be developed via a collaborative, iterative process. The Marin County Board of Supervisors established stakeholder committees at three levels to support community outreach and to provide overall program direction (a complete list of recommended committee members is included at end of this document). Broad community outreach is provided through the Program’s website, the stakeholder process and community meetings.

Description of Stakeholder Committees

Policy Advisory Committee - This group of elected officials is comprised of the District County Supervisor, two representatives from the participating city council, two representatives from each of the appointed flood zone advisory boards and the board of directors of the participating agencies. This committee provides policy input on program direction and community issues and will meet 1-2 times per year.

Operations and Finance Committee- The participating city manager and the Marin County Public Works director will use these meetings to evaluate progress and prioritize funding strategies and will meet 3-4 times per year.

Technical Working Group- This group will include staff of participating state, federal, and local regulatory and participating agencies and community members with a science and technical background. The group 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 will meet at least quarterly to provide input and to review the development of work products.

Community Outreach

Communication to the community at large will be supported by targeted community meetings, presentations at various local boards and homeowners associations, and utilization of the Watershed Program website ( The program website provides dedicated information about the watershed and is regularly updated with notices about workshops, meetings, proposals, and projects. The website platform integrates the Watershed Program with Flood Control and the resources of our MCSTOPPP website.

Community outreach will be developed around these key messages:

  • Working at the watershed scale acknowledges the mutually dependent interactions and linkages between our ridge tops, the valley floor, creeks, and Richardson Bay.
  • The watershed approach acknowledges the need to work collaboratively to identify solutions to reducing flood hazards and improving habitat.
  • Implementation at the watershed scale takes time and is performed in tandem with the on-going maintenance and rehabilitation needs of existing infrastructure.

Tentative Schedule of Meetings and Milestones




Develop a summary of previous studies and existing conditions and data gaps (Tech Memo #1)


TWG meeting to review scope, format, and schedule of WMP, and Tech Memo #1


PAC meeting to discuss preliminary hydrology results (Tech Memo #2) and draft climate change mapping strategies


TWG meeting to review hydrology modeling and strategies for climate change mapping and adaptation


Community meeting proposed


Development of integrated project criteria




PAC meeting to review existing conditions hydraulics modeling results, sea level rise projections and review the list of potential project alternatives


TWG meeting to review existing conditions, hydraulics modeling results, sea level rise projections,and the list of potential CIP project alternatives to be further evaluated


PAC meeting to review recommended alternatives and financial strategy report


TWG meeting to review H&H for alternatives analysis


Release draft WMP for TWG and PAC review




TWG meeting to review draft WMP


PAC meeting to review draft WMP


Community meeting proposed


Final WMP released

Proposed Budget



Existing Conditions and Data Gaps  


Watershed Hydrologic Modeling


Hydraulic Modeling (inc. sea level rise scenarios)    


Climate Change Assessment and Adaptation Strategies


GIS Habitat Mapping        




Alternatives Analysis


Master Plan 


Financial Strategy 


Project Management  


Stakeholder Process 


Outreach (inc. website)  








County of Marin  


City of Mill Valley 


Flood Control Zone 3    


Flood Control Zone 4        





Watershed staffing

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

Southern Marin Flood Protection and Watershed Program

Back to Top


Watershed Overview

Do you live in Mill Valley, Tiburon, Sausalito, Marin City, Tamalpais Valley, or Belvedere?  These communities are linked together by the watershed lands draining to Richardson Bay, a shallow, protected, biologically-rich wildlife preserve.  Mount Tamalpais, the highest point in Marin County, rises steeply above the Bay and its surrounding ridges are protected as public open space and support a myriad of plant and wildlife communities.

Watershed History

Human settlement

The Richardson Bay watershed is located on the aboriginal lands of the Coast Miwok. The arrival of Europeans led to the Mexican government establishing a system of land ownership through which Miwok ancestral lands were divided into tracts of land known as ranchos. Much of the area was originally part of the lands of the Mission San Rafael Archangel, established in 1817. After the Mission was secularized in 1834, the land became the first Mexican land grant in the North Bay. The Rancho Corte Madera del Presidio (literally, “place where wood is cut for the Presidio”) included a sawmill for processing redwood trees, cattle and horse ranches, a brickyard, and a stone quarry.

The city of Mill Valley was incorporated in 1900; the largest single period of growth in the area came when San Franciscans relocated after the 1906 earthquake. Demand for forest resources increased throughout the 19th century; Mill Valley is named for the historic sawmill at Old Mill Park. As forest resources declined due to logging, the land was sub-divided and sold as building lots. In July 1929, a large wildfire burned for three days, consuming 100 homes before shifting winds spared downtown Mill Valley. Continuing demand for development in the area led to many wetlands along the Bay being filled to provide more acreage for construction of residential and commercial buildings, as well as the roads and bridges linking them.

The Sausalito area was explored by Europeans in 1775, when the Spanish ship San Carlos sailed into San Francisco Bay. These explorers named the area Saucelito (“little willows”) after the vegetation spotted from shipboard. Sausalito became an important ferry port, connecting Marin to San Francisco. The railroad brought supplies from the north to be shipped across San Francisco Bay. Marin City, at the north end of Sausalito, grew rapidly during World War II as it was developed for shipyard worker housing.

The Tiburon Peninsula was part of the original grant of Corte Madera del Presidio to John Thomas Reed. When California was admitted to the United States in 1850 after the Mexican war, Angel Island was retained by the government for military use. Military garrisons were established on the island in 1863, providing support to Angel Island and San Francisco military uses, including brickyards and powder companies. A military reservation was built on Peninsula Island (now Belvedere). This subwatershed was also used for ranching and fishing.

In 1852, Benjamin Buckelew laid out “California City” in the area now known as Paradise Cay. Oyster farming, started in Richardson Bay in 1866, lasted for 10 years and a codfish processing plant opened in 1877. A ferry ran from Tiburon to San Francisco and railroad lines connected the community to Sausalito and San Rafael. Shipbreaking and salvage became major industries in Tiburon during the 1880s.

Belvedere incorporated in 1893 and Tiburon in 1964. The entire Peninsula experienced an increase in residential growth after the 1906 earthquake and again when the Golden Gate Bridge opened in 1937. Angel Island went through many transformations, including use as an army hospital, recruit training area, staging area, discharge camp, quarantine station, and immigration station. After World War II, Angel Island was transferred to the Department of the Interior.


Watershed Today

Richardson Bay is considered one of the most “pristine estuaries on the Pacific Coast in spite of its urbanized periphery” (Richardson Bay Audubon 2008 1).  The Bay is recognized as an Important Bird Area (IBA) and is located on the Pacific Flyway, an important migratory bird corridor.  During the winter months, the Bay supports hundreds of thousands of waterbirds, including shorebirds and waterfowl.

Historically, the myriad of habitats in this watershed were connected to one another via the streams cascading down from Mt Tamalpais.  Creeks overflowed onto floodplain marshes and these wetlands transitioned into extensive native forests and grasslands.  Today, the upper slopes and ridges of the watershed remain largely protected from development, and redwood and Douglas fir forest, chaparral, and oak woodlands still dominate the hills.  These plant communities provide wildlife with natural movement corridors.  The diverse vegetation is a reflection of the soils, availability of water and micro-climates in the watershed.  The creeks and adjoining forest lands support steelhead trout and northern spotted owls.



The baylands and Richardson Bay still support a diverse array of native plants and animals.  Great blue heron and great egret nesting colonies are found along the Bay’s shoreline.  Bothin Marsh Open Space Preserve protects the largest salt marsh at the northern end of Richardson Bay.  Surrounded by cordgrass and pickleweed, the marsh supports many birds including the endangered California clapper rail, as well as the endangered salt marsh harvest mouse.

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 in the lower watershed.  Noteworthy species include California black rail, San Pablo song sparrow, salt marsh harvest mouse, and Point Reyes bird’s-beak.  At higher elevations, northern spotted owl territories occur in wooded areas along several creeks.

There is a small population of California red-legged frog (CRLF), federally listed as threatened and a California Species of Special Concern, on the Tiburon Peninsula (CDFG 2008).  The population was discovered in 1997 at a small pond, formerly a lagoon, at Keil Cove.  A second sighting was made in 2000 in coast live oak woodland to the northwest of the Keil Cove sighting.  This is probably the last remaining population on the peninsula.

The Arroyo Corte Madera del Presidio subwatershed still supports a steelhead trout run. Old Mill and Cascade Creeks support the healthiest remaining fisheries habitat in the watershed.  Due to their ephemeral nature, the small creeks draining directly to Richardson Bay do not support sustainable fisheries.

The Arroyo Corte Madera del Presidio subwatershed is known to support nine fish species (seven native and two introduced).  Native species include California roach, Sacramento pikeminnow, Coho salmon, steelhead trout, threespine stickleback, and staghorn and prickly sculpins.  Introduced species include rainwater killifish and western mosquitofish (Leidy 2007 2).  Recorded observations of Coho date from the 1940s to 1960s; Coho were last seen in 1981 (Leidy, et al., 2005 3).  Steelhead, federally listed as a threatened species, continue to inhabit Arroyo Corte Madera del Presidio in reduced numbers.

Barriers to fish passage in our local creeks can consist of road crossings and undersized culverts when they block passage for fish at any life stage.  Fish passage considerations must be made for the young fish as well as adults.



Richardson Bay itself supports the second largest extant eelgrass bed in San Francisco Bay.  Eelgrass beds provide important shelter for fish and shellfish, and a food source for many water bird species.  Bay pipefish, bat ray, black surfperch, northern anchovy, Pacific herring, striped bass, and threespine stickleback are just a few of the many fish species found in the Bay.

In the winter, the Bay supports hundreds of thousands waterbirds including ducks, geese, grebes and shorebirds.  The Richardson Bay Audubon Center and Sanctuary manages a small upland parcel, supporting beach, bluffs, grasslands, oak woodland, coastal scrub, and riparian woodland, and 900 acres of submerged baylands.  The Center operates a Monitoring Avian Productivity and Survivorship (MAPS) bird-banding station during the breeding season.  Species captured and/or observed during the breeding season include Cooper’s hawk, Anna’s hummingbird, Pacific-slope flycatcher, black phoebe, western scrub-jay, chestnut-backed chickadee, bushtit, Bewick’s wren, Swainson’s thrush, northern mockingbird, Wilson’s warbler, spotted towhee, California towhee, dark-eyed junco, black-headed grosbeak, red-tailed hawk, mourning dove, American crow, common raven, barn swallow, cliff swallow, house finch.  In addition, the Center is working on eelgrass bed restoration, native oyster restoration, fish monitoring, water quality monitoring, and waterbird surveys.

Human habitation and land use

Land UseImperviousness

Land Use                                        Imperviousness

Mill Valley land use is mostly medium to low density residential with clusters of commercial areas on the valley floors.  The upper slopes and ridges are largely owned by Marin County Open Space, Marin Municipal Water District, and state and federal park agencies; these lands provide habitat connectivity between adjoining watersheds.

The Coyote Creek area is bounded by Bothin Marsh and Richardson Bay to the east and the Arroyo Corte Madera del Presidio subwatershed to the north.  The ridges to the south and west are protected as part of the Golden Gate National Recreation Area.  The Coyote Creek subwatershed includes the unincorporated communities of Tamalpais Valley, Tamalpais Valley Junction (Tam Junction), Manzanita, and Almonte.

Most of the development is single-family residential, with limited commercial development and services.  The upper watershed is mostly rural and semi-rural, while the lower watershed is developed with greater densities near Bothin Marsh.  Commercial development is largely concentrated in a small area at the junction of Highway 1 and Almonte Road.

Sausalito and Marin City both have a mix of residential and commercial areas.  The upper hillsides are almost entirely residential and there is a substantial houseboat residential area at along the bay front.  Marin City has less waterfront; commercial development is in the lower bayfront areas and the residential development is in the hills.

In addition to Tiburon and Belvedere, the Peninsula supports Bel Aire, Paradise Cay, and Strawberry Point.  Development is largely residential, with small commercial areas. The largest preserve in the watershed is Ring Mountain Preserve, located on Tiburon Ridge.  The Richardson Bay Audubon Center and Sanctuary manages an 11-acre upland parcel directly adjacent to Richardson Bay and 900 acres of submerged baylands.  This property supports beach, bluffs, grasslands, oak woodland, coastal scrub, and riparian woodland.

2 Ecology, Assemblage Structure, Distribution & Status of Fishes in Streams Tributary to the San Francisco Estuary

3 (Oncorhynchus mykiss) in Streams of the San Francisco Estuary, CA