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Monterey's San Clemente Dam Removal Project

The History of the San Clemente Dam
The San Clemente Dam was built in 1921 in upper Carmel Valley to supply water to the then-burgeoning population and tourism industry on the Monterey Peninsula – an area which has a semi-arid climate and few year-round water sources. With demand for water increasing every year, the answer was a 106-foot high concrete-arch dam approximately 18 miles from the ocean on the Carmel River. The original San Clemente Reservoir capacity of approximately 1,425 acre-feet was essential to meet the water supply needs of the 1930s and for several decades thereafter. But the Carmel River naturally brings sediment from the mountains to the beaches – sediment which over time collected behind the dam, slowly filling over 90 percent of the reservoir with debris and eroded soil. The San Clemente Reservoir no longer serves an important water supply function. The communities of the Monterey Peninsula now get their water from wells in Carmel Valley and Seaside.

At the time of construction, little was known about building for earthquake safety. Between 1980 and 1992, studies were performed to determine the safety of the San Clemente Dam in the event of a major earthquake on the nearby Tularcitos fault, or a flood caused by a very large storm. In 1992, the California Department of Water Resources, Division of Safety of Dams (DSOD), required that California American Water, as the current owner and operator of the San Clemente Dam, upgrade it to comply with modern seismic safety standards. DSOD also ordered interim safety measures be taken, including an annual drawdown of the reservoir, which required drilling holes through the dam to release hydraulic pressure. Work in excess of $1 million was completed, with the first annual draw-down performed in 2003. In addition, various measures to protect the threatened Central Coast steelhead trout and California red-legged frog were implemented, and an evacuation plan for residents down-stream of the dam was developed in cooperation with the Monterey County Office of Emergency Services and the Carmel Valley Fire Department.

The Challenges and the Remedy Options
Since the mid-1990s, multiple engineering and environmental studies have been prepared by California American Water and DSOD to determine what should be done to improve the dam for safety and environmental protection. The option to reroute the river and remove the dam in December 2007, DSOD certified a Final Environmental Impact Report (FEIR) that analyzed potential impacts to geology and soils, hydrology and water resources, water quality, vegetation and wildlife, wetlands, air quality and noise. The FEIR concluded that adding a steel-reinforced layer of concrete to the dam would minimize risk of dam failure in an earthquake or flood, and that installing a state-of-the-art fish ladder would be an environmentally acceptable method to ensure survival of the Carmel River’s steelhead trout population. The total cost of this dam strengthening project was estimated at $50 million.

At the request of DSOD, California American Water also commissioned engineering and environmental studies to evaluate the possibility of removing the dam, while retaining the accumulated silt on-site and rerouting the river. The estimated the cost of this alternative project is approximately $85 million. The option to reroute and removal project received a great deal of support from resource protection agencies, as well as environmental protection groups such as the Carmel River Watershed Conservancy, Carmel River Steelhead Association and the California Planning and Conservation League who supported removing the dam because it serves as a barrier to threatened Central Coast Steelhead Trout. By removing the dam, steelhead will have unimpaired access to over 25 miles of natural spawning and rearing habitat.

The Solution: A Unique Project, and Unique Partnership
In January, 2010, a formal agreement was reached with California American Water and federal, state and local agencies that provides a framework to cooperatively remove the dam. It enables California American Water to resolve dam safety concerns through the lowest cost solution for ratepayers. Public agencies, led by State Coastal Conservancy and National Marine Fisheries Service, will secure additional funds to pay for the dam removal project. This project demonstrates when public and private interests work together, benefits are realized far beyond what either could achieve alone. By overcoming numerous political and procedural challenges, Monterey's San Clemente Dam Removal Project can be a model for other public-private cooperative efforts.

Benefits of the Project

  • Provide Jobs and Local Economic Stimulus
    The project’s direct construction expenses of approximately $62 million are projected to result in over $150 million in economic output that will save or generate over 900 jobs. Monterey County has been hard hit by the recession and currently has an unemployment rate over 12%.
  • Permanently Improve Public Safety
    Removing the dam will permanently resolve a threat to 1,500 structures in the downstream floodplain that are now threatened by dam collapse.
  • A Model for Western Dam Removal Projects
    The San Clemente Dam will be one of the largest dams removed in the West. There is a great opportunity to learn more about post-dam removal sediment transport, channel response, and river restoration processes from studying the outcomes of the project. The project team has invited a group of academic experts to develop a coordinated research program for the project that will help guide all future dam removal projects in the West.
  • Restoring Connectivity and Recovering Species
    Steelhead along California’s Central Coast are a threatened species. Removing the San Clemente Dam will restore access to 25 miles of spawning and rearing habitat, critical to steelhead recovery. Restoring the river’s ecological connectivity will benefit threatened species like the Central Coast steelhead trout and the California red-legged frog. Enabling sediment to move past the dam will also help replenish sand supply to Carmel River beach and dunes, fortifying the beach and coastal area against sea level rise. Flowing through the Ventana Wilderness and the Los Padres National Forest, the Carmel River is one of the best opportunities for river restoration on California’s Central Coast. The San Clemente Dam has impacted the Carmel River and its wildlife since 1921. The river suffers accelerated erosion, the once-vibrant steelhead run has dramatically decreased, and lives and property below the dam are threatened with potential collapse of the dam, deemed unsafe by the State of California. Furthermore, the dam no longer provides a drinking water supply, as its reservoir is now 90% filled with sediment.
  • Coordinated River Restoration Program
    Removal of the San Clemente Dam is part of a larger coordinated effort to restore the Carmel River. This larger effort will restore the lagoon and floodplain, increase instream flows, and restore the river’s riparian corridor.
  • Permanent Watershed Conservation and Public Access
    After completion of the project, California American Water will donate 928 acres of adjacent land to the Bureau of Land Management for permanent watershed conservation and compatible public access. The project area adjoins two regional parks, creating over 5,400 acres of combined open space available for hiking and passive recreation. In addition, the restored river channel enables whitewater kayaking, a new regional recreational amenity.

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