Bothin Marsh: Wave Data Collection


SCH Number
Public Agency
Marin County Open Space District (MCOSD)
Document Title
Bothin Marsh: Wave Data Collection
Document Type
NOE - Notice of Exemption
Document Description
Marin County Open Space District (MCOSD) is proposing to install a temporary equipment with the purpose of measuring wave conditions in north Richardson Bay near the shoreline of the Bothin Marsh Preserve. Equipment would include a sonic wave sensor and a high frequency pressure transducer. The instruments would be installed for approximately three months, between January and April 2024. The sonic wave sensor would be installed on the mudflat approximately 200 feet offshore of South Bothin Marsh. It would measure wave heights over the mudflat approaching the marsh shoreline and would consist of two units: the sonic wave sensor and a data collector unit with attached solar panel. Each of the two units would be mounted on a galvanized steel pipe, or similar, that would be temporarily embedded in unvegetated mudflat. Each pipe would be approximately 12-15 feet long and approximately 3 inches in diameter. Each pipe would be driven into the mud deep enough to provide a stable platform that will not move or tilt under anticipated wave conditions. The instruments would be mounted to the top of the pipe, approximately 8 feet above the mudflat, and at least 2 feet above typical high tide elevations. The footprint of each pipe and attached instruments would be less than one square foot. The installation would be performed using handheld tools including hammers, wrenches, and screwdrivers. The pressure transducer would be installed on the seabed in the deep channel east of the Highway 101 Bridge. It would measure offshore tide elevations and to provide a measurement of wave heights at a deepwater location (to measure waves during low tides when the mudflat at the sonic sensor is dry). The plastic and metal frame would be lowered to rest on the seabed and its footprint would be less than 10 square feet. The pressure transducer would then be attached to the frame along with two marine grade rigging lines that would be used to lower the instrument into place and to recover the instrument at the end of the deployment. These lines may include sections of chain or attached ballast weights to prevent the lines from floating and reduce the risk of tangling/snags. The free end of the lines will be attached to a high-visibility buoy or secured to one of the nearby bridge piers. The proposed instrument installation is anticipated to have a de minimis impact to surface waters due to the very small footprint of the instruments; the short duration of the instrument installation; no vegetation would be removed to install, monitor, or remove the equipment; and no disturbance to wildlife is anticipated. All installed instruments and mounting hardware would be suitable for contact with coastal waters and would be free from harmful coatings and other pollutants. All work would be performed by experienced field technicians who are familiar with safe watercraft operations, marine instrument installation, and work in and around sensitive aquatic habitats.

Contact Information

Kelly Hyde
Agency Name
Marin County Open Space District
Job Title
Assistant Open Space Planner
Contact Types
Lead/Public Agency


Mill Valley
Cross Streets
Shoreline Hwy at Highway 101
Total Acres
Parcel #
052-350-33, 059-310-01
State Highways
Mill Valley Middle, Tamalpais High, Edna Maguire Elementary
Richardson Bay and Coyote Creek

Notice of Exemption

Exempt Status
Categorical Exemption
Type, Section or Code
Section 15306: Information Collection
Reasons for Exemption
The proposed project consists of the MCOSD conducting basic data collection, research, experimental management, and resource evaluation activities which do not result in a serious or major disturbance to an environmental resource for the purpose of gathering information to inform the proposed Evolving Shorelines Project at Bothin Marsh, for which a separate environmental document would be prepared in compliance with the California Environmental Quality Act. Implementation of the proposed project would not result in significant impacts based on location and would not impact an environmental resource or any designated environmental resource of critical concern. The project area is not located on a hazardous waste site pursuant to Government Code Section 65962.5 or within a state scenic highway. Implementation of the proposed project would not affect scenic resources, historical buildings, rock outcroppings, result in cumulative impacts; or result in a significant effect to the environment due to unusual circumstances.
County Clerk


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