The reservoir behind Matilija Dam is almost completely filled in with sediment, significantly reducing storage capacity to the point of rendering the dam nonfunctional. With no fish ladder or bypass structure present, it is a complete barrier to the migration of endangered Southern California steelhead. The dam also causes increased water temperatures, an altered flow regime, and deprives the lower watershed, estuary, and beaches of sediment. Southern California steelhead are an incredibly important species because they evolved in seasonally disconnected systems and are able to survive in warmer waters than are other steelhead populations. With only an estimated 500 individuals remaining, this life history trait makes this a particularly valuable population to protect in the face of climate change. Dam removal will reconnect access to critical steelhead habitat and help with the recovery of steelhead in Southern California. The removal of Matilija Dam will restore access to 17 miles of spawning, rearing and foraging habitat above the dam.
For almost 20 years a broad coalition of community groups and resource agencies have been advocating for dam removal and working together to develop a comprehensive strategy to restore the Ventura River. Ventura County officially made the decision in 1998 to remove the dam altogether. Congressional approval for a preferred preliminary design was obtained through the Water Resources Development Act of 2007, but was not funded. The Matilija Dam Ecosystem Restoration Project will cost millions of dollars and the lack of dedicated funding has been a major impediment to action. Other factors, such as determining the proper sediment release strategy, the need to modify downstream roads, levees and bridges, and the effect of the Thomas Fire on the landscape all add to the challenges of the undertaking. Regardless, all stakeholders agree, Matilija Dam must come down.
In March 2016, the group overseeing design alternatives voted in favor of a removal plan. The approved alternative will use two boreholes in the dam itself to erode and transport as much sediment as possible during the first few high flow events once they are opened. This concept represents a “natural transport” alternative that concentrates the bulk of transport of the trapped sediment to the first few storm events. This alternative will minimize ecologic impact downstream and also lower the overall project cost by reducing the need to truck material out of the reservoir. Current projections estimate that once the boreholes are opened, complete dam removal and a free-flowing river will be achieved in two to five years. Releasing sediment through placed boreholes was demonstrated with success in 2011 on the Condit Dam in Washington State. Currently, the technical studies and planning needed to execute this alternative are ongoing. The Matilija Dam Ecosystem Restoration Project funding committee is actively pursuing all funding strategies to complete the required upgrades to bridges, roads and levees and fully fund dam removal. In May 2017, with resources from a California Department of Fish and Wildlife Proposition 1 grant, the project secured funding for the next step of the dam removal process.
Gough, S. 2007. River geomorphology videos. DVD. Little River Research & Design, Carbondale, IL; www.emriver.com
This is the back side of the dam with the water drained out of the reservoir.
Matilija reservoir is full of sediment, about 6 million cubic yards to be exact.
This has reduced its capacity by over 90% rending it an obsolete structure that no longer serves a purpose for flood control or water storage.
The dam’s effectiveness as a sediment trap has resulted in the erosion of beaches downstream that rely upon the Ventura River.
The reservoir storage is predicted to be zero by 2020.
So what’s the plan to remove the sediment? It’s called “Full Dam Removal with Short-Term Sediment Stabilization on Ste” and under this plan, the immediate passage will be restored for the native steelhead trout, and controlled releases of sediment will gradually restore the natural riverine processes that nourish coastal beaches.
The fundamental challenge of dam removal is sediment management. The Feasibility Study determined that “Full Dam Removal with Short-Term Sediment Stabilization” was determined to be the best overall concept, given the watershed hydrology and constraints. The primary design constraint is floodplain development downstream of the dam. Residences, roads and bridges, and water supply facilities all need to be protected under any project alternative. Approximately 2 million cubic yards of fine sediments currently trapped in the reservoir area will be slurried downstream. The remaining 4 million cubic yards will be stored upstream of the dam site as illustrated.
Ventura County Watershed Protection District
Ventura River
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List of StakeholdersVentura County Watershed Protection District
California Department of Fish and Wildlife
Matilija Coalition
Patagonia
CalTrout,
State Coastal Conservancy
Surfrider Foundation
National Marine Fisheries Service
Wildlife Conservation Board
Help build the Matilija Coalition: Show your support for the removal of Matilija Dam as a sign-on group or individual. Vote for natural resource funding. Contact your local representative and ask for the line items in budgets that designate funds
Help usPeter Moyle is the Distinguished Professor Emeritus in the Department of Wildlife, Fish and Conservation Biology and Associate Director of the Center for Watershed Sciences, at UC Davis. He is author or co-author of more than 240 publications, including the definitive Inland Fishes of California (2002). He is co-author of the 2017 book, Floodplains: Processes and Management for Ecosystem Services. His research interests include conservation of aquatic species, habitats, and ecosystems, including salmon; ecology of fishes of the San Francisco Estuary; ecology of California stream fishes; impact of introduced aquatic organisms; and use of floodplains by fish.
Robert Lusardi is the California Trout/UC Davis Wild and Coldwater Fish Researcher focused on establishing the basis for long-term science specific to California Trout’s wild and coldwater fish initiatives. His work bridges the widening gap between academic science and applied conservation policy, ensuring that rapidly developing science informs conservation projects throughout California. Dr. Lusardi resides at the UC Davis Center for Watershed Sciences and works closely with Dr. Peter Moyle on numerous projects to help inform California Trout conservation policy. His recent research interests include Coho salmon on the Shasta River, the ecology of volcanic spring-fed rivers, inland trout conservation and management, and policy implications of trap and haul programs for anadromous fishes in California.
Patrick Samuel is the Conservation Program Coordinator for California Trout, a position he has held for almost two years, where he coordinates special research projects for California Trout, including the State of the Salmonids report. Prior to joining CalTrout, he worked with the Fisheries Leadership & Sustainability Forum, a non-profit that supports the eight federal regional fishery management councils around the country. Patrick got his start in fisheries as an undergraduate intern with NOAA Fisheries Protected Resources Division in Sacramento, and in his first field job as a crew member of the California Department of Fish & Wildlife’s Wild and Heritage Trout Program.