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Project Description
Nicasio Reservoir was created by the construction of Seeger Dam, an earthen filled dam on Nicasio Creek in 1960. The reservoir's current storage capacity is 22,340 acre-feet. This project would install a 280-foot-long, 4.4-foot-high inflatable rubber gate spanning the width of the existing spillway crest of Seeger Dam to increase the capacity at Nicasio Reservoir by approximately 3,700 acre-feet. Modifying Nicasio Reservoir’s spillway is one of the near-term storage enlargement projects identified in the District's Water Supply Roadmap.
Environmental Review Process
Pursuant to the California Environmental Quality Act, Marin Water is initiating environmental review of the proposed Nicasio Spillway Modification Project.
Public Comment Period for the Scope of the Environmental Review
The review begins with a comment period for agencies and the public to comment on the scope of the environmental review, including the project description, environmental issues to be analyzed and potential alternatives. The issues are described in a Notice of Preparation.
| Notice – scoping public comment period extended In mid-May, Marin water extended the public comment period and added another public meeting for collecting input on what to include in the scope for the Project’s environmental review. The information below has been updated to reflect the changes in the original public comment period schedule. |
The public comment period is open April 30, 2025, and until 5 p.m. Aug. 4, 2025. Comments must be submitted before the deadline and may be provided in one of the following ways:
- By email to:
Elysha Irish at eirish@marinwater.org
Subject: Nicasio Spillway Modification Project public comment
OR
- By U.S. postal mail to:
Marin Water
Attention: Elysha Irish
220 Nellen Ave.
Corte Madera, CA 94925
Scoping Meetings
As part of the environmental review process, Marin Water is holding three public scoping meetings. These meetings are an opportunity for interested parties to learn more about the project and provide public comments. The information presented will be the same for all three meetings.
Presentation for EIR Scoping Meetings
- Scoping Meeting 1 – Thurs, May 22 – Video Recording
- Scoping Meeting 2 – Tues, May 27 – Video Recording
- Scoping Meeting 3
Tuesday July 15, 1:00 – 3:00 p.m.
This is a virtual Zoom meeting – https://marinwater.zoom.us/j/83247604594
Dial-in Number: 1-669-444-9171 Webinar ID: 832 4760 4594
Ongoing Surveys
Various surveys are needed to inform the environmental review and planning for this proposed project. These surveys include environmental surveys, topographic boundary surveys, and surveys of Halleck and Nicasio Creeks.
The table below provides additional information about the surveys including what the survey entails, its current status, the purpose, and the location of the properties that Marin Water proposes to survey. The surveys will provide critical insights to support Marin Water’s efforts to gain a more comprehensive understanding of the surrounding area as we investigate the potential effects of the proposed project.
For each survey, property owners will be contacted on an individual basis for property access as more detailed timing is known as it relates to each identified parcel.
Survey type: Environmental
| What is it? | There are a variety of surveys in this group including, but not limited to, wetland delineation, habitat and plant surveys, cultural (archeological and historical resource). |
| Why is it happening? | To investigate the issues that need to be evaluated as part of the environmental impact report and approvals from resource agencies. |
| Who is being contacted? | Property owners in the area potentially affected by implementation of the proposed project. |
| What is the current status? | Mostly completed. Surveys of historic properties are still in progress. There may be some additional areas identified for further review and property owners in these areas will be contacted. |
Survey type: Boundary
| What is it? | Obtains property boundary information for Marin Water parcels. |
| Why is it happening? | To validate Marin Water parcel boundaries. |
| Who is being contacted? | Property owners adjacent to Marin Water property on the southern portion of the Nicasio Reservoir. |
| What is the current status? | This field work is estimated to begin in mid-July. |
Survey type: Creeks
| What is it? | Obtain data (elevation survey measurements, photographs) on topography and channel depth of Nicasio and Halleck creeks. Collect sediment samples and other information about grain size of sediment in the creeks. |
| Why is it happening? | To support the development of hydrologic and sediment transport models to better understand existing conditions and how proposed project operations may affect water levels and sediment movement in the creeks. |
| Who is being contacted? | Property owners adjacent to Nicasio Creek from Nicasio Reservoir to Lucas Valley Road and Halleck Creek from the reservoir up to the quarry. |
| What is the current status? | Actively in progress. |
Outreach and Engagement Presentations
Background
Marin Water supplies water to more than 191,000 people in central and southern Marin. About 75% of the District's water supply originates from rainfall on the Mount Tamalpais Watershed and in the hills of west Marin. That water flows into the District’s seven reservoirs, which hold nearly 80,000 acre-feet of water. Supplies from Marin Water's local watersheds are generally sufficient in most years and of high quality.
Marin Water supplements its local rainfall supplies with water imported from the Russian River system in Sonoma County and with recycled water. Together these supplemental supplies account annually for about 25 percent of Marin Water’s supply. Through its award-winning Water Efficiency programs, Marin Water also works to reduce demand.
Historically, Marin Water has successfully met water supply demands during periods of extreme drought with a combination of conservation and increased Sonoma Water supplies. However, Marin Water’s most recent drought risk assessment indicates that even with implementation of its established water shortage contingency plan, Marin Water would still experience a supply shortfall during periods of extreme drought. In addition, recent studies indicate that severe droughts are projected to become much more frequent as a result of changing climate conditions.
Benefits
The project is a relatively cost-effective way to achieve additional water storage capacity in a shorter timeframe as compared to other, longer-term water supply alternatives within the District’s Water Supply Roadmap. The additional water supply yielded would help increase the District's water supply resiliency during future droughts.
Estimated Schedule and Status
Marin Water is currently developing the designs of the proposed spillway raise, conducting the environmental review of the project, and coordinating with regulatory agencies and potentially affected landowners.
Public comment on the scope of the environmental review and Notice of Preparation will run from April 30, 2025 and until 5:00 p.m., August 4, 2025.
Planning & Design: Summer 2024 - Spring 2026
Construction: 2027
Funding Sources
Capital Maintenance Fund | Other Funding Sources | Total |
$15,000,000 | - | $15,000,000 |
| Project | Nicasio Spillway Modification Project |
| Program | General Improvement | A1A05 Dams and Reservoirs |
| Project Number | D25007 |
| Contact | Matthew Steiner | msteiner@marinwater.org |