Matilija Coalition - Feasibility Study

Removing Matilija Dam is no small task in a watershed that has seen significant changes since dam construction was completed in 1948. But after three years of study, a plan has been developed to restore the imperiled Ventura River ecosystem by removing the largest dam to date. “Full Dam Removal with Short-Term Sediment Stabilization on Site” evolved as the best way to deal with the sediment issue that vexes every large dam being considered for removal. Under this plan, 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. Studies show that this approach, along with additional engineering features and a long-term adaptive management plan, will fully mitigate the potential downstream impacts from the project.

The diagram below describes the plan, as described in the Public Draft Report dated July 2004. Further information is included in our newsletter Matilija Messenger 7. Technical documents may be downloaded from www.matilijadam.org

The flowchart above illustrates the phases of the Feasibility Study that will lead to a final plan for Matilija Dam. The first phase, a “Baseline Conditions (F3) Report,” was completed in October 2002. The report concludes that since the watershed ecosystem will remain degraded with the dam in place, there is a need for a restoration project.

The next phase of the feasibility study will evaluate various project alternatives for their ecosystem restoration potential and their cost and technical feasibility. A preferred project alternative is selected according to the environmental study and a cost/benefit analysis that places a value on future benefits to the ecosystem. (See Matilija Messenger Vol. 4 for more on Habitat Evaluation Procedure (HEP) analysis.)

Once a preferred alternative has been selected, there will be a public meeting with opportunities for public review and comment. Then the final design and Environmental Impact Statement (EIS) will be completed in preparation for the deconstruction of Matilija Dam. The current schedule is for completion of the study by the end of 2004. Implementation will depend upon funding.
The Baseline Conditions “F3 Report” and other technical studies may be accessed at www.matilijadam.org.

The Matilija Dam Ecosystem Restoration Feasibility Study began in the summer of 2001. The Army Corps of Engineers is the lead agency in a collaborative effort that includes many federal, state, and local government agencies. The goal is to determine the preferred method for removing the dam to restore the Ventura River ecosystem, while considering all the environmental risks and benefits.

Since a dam of this type and size has never before been decommissioned, many areas of study are required to ensure success. The first step is to establish a "baseline", a detailed description of currently existing conditions in the watershed. Survey and Mapping will be performed to develop an accurate model of the watershed. Geotechnical Investigations will use the sediment core samples to characterize the sizes, distribution and content of sediments impounded behind the dam, and further fieldwork will characterize the riverbed downstream. Civil and Structural Design surveys will determine the structural condition of the concrete dam for the design of potential deconstruction methods.

Hydrology and Hydraulic Studies will determine the erodability of deposits within the reservoir and the rate of sediment release that can be tolerated by downstream structures and aquatic ecosystems. Coastal Studies will examine effects on the environment at the mouth of the Ventura River and the potential for beach nourishment.

The most critical element of the engineering studies is Sediment Transport Studies. This work will use all the information obtained from the fieldwork and subsequent analyses to develop computer simulations of the alternative removal scenarios. These simulations will determine the effectiveness of each approach and impacts on the watershed. Plan Formulation/Alternative Analysis will use all the technical information generated by these engineering studies to determine the preferred alternative for the final project.

In addition to the engineering studies, Environmental Studies will include biological surveys and assessment of existing habitat, and an assessment of the future habitats to be restored by dam removal. This information is the critical link in the feasibility of the project, since federal funding will depend on the potential for Ecosystem Restoration as valued by these studies.

More information and updates on the Feasibility Study are posted on the web at www.matilijadam.org

On June 5, 2001 the Ventura County Board of Supervisors approved a cost share agreement with the US Army Corps of Engineers for a Feasibility Study for Matilija Dam. The Feasibility Study is expected to take 3.5 years and cost $4.2 million.

The Feasibility Study will progress according to a Project Management Plan completed in May 2001. This document may be downloaded at www.matilijadam.org