Greenwood Gravel Beach Design Project

Marin County Department of Public Works
Greenwood Beach Currently
Grant Amount:

$380,000

Location:

Greenwood Beach, Town of Tiburon, Marin County Measure AA Region: North Bay

Project Phases Funded by this Grant:

Develop detailed designs and specifications, prepare permit applications, and complete CEQA review

Measure AA Program Category:

Vital Fish, Bird and Wildlife Habitat Program; Integrated Flood Protection Program

Partners:

Marin Community Foundation, California State Coastal Conservancy

Summary:

The purpose of the project is to develop detailed designs and specifications, prepare permit applications, and complete CEQA review for a natural bay beach design at Greenwood Beach in Marin County. The project aims to demonstrate that bay beaches as a living shoreline design approach are a viable alternative to riprap and seawalls. Living shoreline techniques reinforce the shoreline and minimize coastal erosion, while restoring natural habitats for estuarine and coastal organisms. Through strategic placement of native vegetation and natural materials such as sand, gravel, and cobble, bay beaches can protect tidal marshes behind them from further erosion. Building on preliminary designs funded through a partnership between the Marin Community Foundation and California State Coastal Conservancy, the project will develop near-final designs for a gravel beach that will provide nature-based shoreline protection and enhance valuable coarse-grained beach habitat. The goal of the project is to complete CEQA documentation and permit applications and be ready for final design and implementation of the gravel beach design.

Greenwood Beach is the beach along a much-loved public park in Tiburon, Marin County. The project site was historically a larger, wider barrier beach that sheltered a non-tidal salt marsh with shallow seasonal ponds. The shoreline now includes broad intertidal mudflats, a flood channel delta, a small salt marsh patch, and two small pocket beaches, surrounded by old bay fill and shoreline armoring. The west end of the beach is well-used for recreation, but the rocky concrete and asphalt shoreline around it is avoided.

Over the years more fill of asphalt, concrete rubble, and sand has been placed to combat wave erosion at the park shoreline. The wave erosion has been scattering the fill across the mudflats. The boulders and angular asphalt and concrete rubble coupled with the eroding vertical shoreline make this area of Greenwood Beach potentially hazardous and poor wildlife habitat. As the shoreline erodes further, more asphalt and concrete rubble may be deposited into the bay.

The project can support substantial habitat benefits through enhancing the beach system and marsh area behind the beach. Constructed bay beaches can provide breeding or foraging habitat for Forster’s terns, black-necked stilts, American avocets, black oystercatchers, and other shorebirds. Bay beaches can also provide unvegetated, high-tide roosts for shorebirds and hightide refuge for marsh wildlife. The backshore of the project site would be designed have gentle slopes that can support native salt-tolerant shoreline vegetation, such as gumplant, pickleweed, and California sea-blite.

The shoreline conditions found at Greenwood Beach are common to many areas along the San Francisco Bay shoreline. This project would serve regional significance by providing a publicly accessible design-with-nature model for similar locations around San Francisco Bay.

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