Dam Spillway Repairs

Collage of five images shows five different spillways, and, from left, work being done on a spillway, water flowing down a spillway, an empty spillway, work being done on a spillway, and water flowing down a spillway.
Collage of five images shows five different spillways, and, from left, work being done on a spillway, water flowing down a spillway, an empty spillway, work being done on a spillway, and water flowing down a spillway.

Following the 2017 failure of the concrete spillway on Oroville Dam, the California Division of Safety of Dams (DSOD) directed dam owners throughout California to perform additional evaluations of spillways with similar construction as Oroville Spillway. Marin Water identified the dams at Soulajule, Nicasio and Kent reservoirs as the District-owned dams with similar construction. Through coordination with the Division of Safety of Dams, Marin Water used a multi-phase assessment approach, including record reviews, field inspections, subsurface investigations, and structural analyses completed over several years.

Assessment & Results

Phase I (2017-2021): A high-level evaluation of the Seeger Dam, Peters Dam and Soulajule Dam spillways identified routine non-structural maintenance items, including crack repairs, joint sealing and drain cleaning. Those non-structural spillway repair activities were completed in 2021 in accordance with DSOD guidance. 

Image shows water flowing through a spillway.

Phase II (2022-2025): At DSOD’s direction, a more detailed subsurface investigation evaluated the structural condition of Seeger Dam, Peter’s Dam, and Soulajule spillway using ground penetrating radar, concrete coring and video inspections of the underdrain system. The completed engineering reports were submitted to DSOD in April 2025. 

  • As a result of the more detailed investigation in Phase II, DSOD directed Marin Water to develop a modernization plan for the Seeger Dam Spillway. Marin Water is currently in the planning phase of the Seeger Spillway Modernization Project. Learn more.

Project Cost

The Dam Spillway Repairs undertaken at Soulajule, Nicasio and Kent reservoirs cost about $2.2 million combined. This work helped shape the coming investment in Seeger Dam at Nicasio Reservoir. The current modernization project at Seeger Dam is the result of this multi-year engineering and regulatory process, with each phase building on the findings of the previous phase under DSOD’s oversight.