Matilija Dam Removal Feasibility Study

Location: Ventura County

Project Type: Restoration Planning

Status: Completed

Habitat Type: fish passage, sedimentation

Cost: $5,150,000

Assembly District: 37

Senate District: 19

Congressional District: 26

Project Lead/Grantee:
Ventura County Watershed Protection District (805-654-2040)

This project prepared a feasibility study for removal of Matilija Dam on the Ventura River. 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 erodibility 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.