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Matilija Dam Ecosystem Restoration Project Fine Sediment Study Group Final Report
Mary Selkirk
Date Created and/or Issued
Publication Information
Center for Collaborative Policy, CSU Sacramento
Contributing Institution
UC Riverside, Library, Water Resources Collections and Archives
Clearinghouse for Dam Removal Information (CDRI)
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Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user.
Scope/Content: Abstract: In the fall and winter of 2010, the Ventura County Watershed Protection District (VCWPD), the U.S. Army Corps of Engineers (Corps) and the State Coastal Conservancy convened a focused study group of key stakeholders to discuss issues relating to the management of the fine sediments that are sequestered behind Matilija Dam. Management of the fine sediments is perhaps the key unresolved problem currently facing the proposed removal of Matilija Dam, as well as implementation of the associated ecosystem restoration program on the Ventura River. The primary goals of the facilitation included identifying technical studies and other investigations that could help produce a consensus solution for fines sediment management that would still conform, to the extent practicable, to the existing environmental and decision documents for the Matilija project. During the course of four full-day meetings directed by a professional facilitator, the sediment management study group worked together in a collaborative problem-solving process to: - _Define the problems and establish a common understanding of existing options to manage the fine sediments; - _Identify the key concerns and technical questions that needed to be addressed to resolve the fine sediment issue; - _List important operational, regulatory, and environmental constraints; and - _Identify and prioritize the key "data gaps" and information needs that should be the subject of additional technical studies and investigations. Among the major questions that the Study Group explored in its initial meetings were: What options can be considered to address cost reductions and more acceptable environmental and social impacts associated with the slurry of approximately 2 million cubic yards of fine sediment from Matilija Dam to the Baldwin Road Disposal Area (BRDA) sites, as described in Alternative 4b in the Feasibility Study? What risks do the fine sediments pose to the public water supply and the operations of the water districts, and how do we quantify those risks? How can the Matilija project benefit from pre- and post-removal analyses of other large dam removal projects? And what are the environmental thresholds of fine sediments in the water column for steelhead and other beneficial uses? During the third meeting, the Study Group agreed that key problem statements and data gaps should be nested within a few scenarios that would conceptually describe alternate (but not necessarily mutually-exclusive) approaches to resolving the fine sediment management issue. The Study Group then focused on three main options: - _Optimize Alternative 4b: Modifications to Alternative 4b (slurry to the Baldwin Road Disposal Areas) to reduce the cost of that option and improve its technical feasibility. - _Hybrid option: Modifications to Alternative 4b to reduce the amount of water and sediment that must be slurried to the BRDA sites. The potential components of this option could include notching the dam to the existing sediment level and incorporating a large amount of the fines into the natural restoration of Matilija Canyon. - _Full notching and phased natural transport: This option would replace slurry to BRDA with a solution that could include full notching; phased or metered natural transport of fine material; and/or transporting sediment flows by conduit to some point below the Robles Diversion; and/or delivery of "clean" water from upstream of Matilija Reservoir to downstream water agencies. Its primary goal would be to avoid slurry of any material downstream. The Study Group then used this framework to further define key constraints and the priority data gaps and information needs to be addressed by additional investigations if a viable consensus solution is to be developed for managing the fines. The use of the proposed strawman framework enabled the Group members to consider combinations of investigations that met the test of optimizing Alternative 4b, by maximizing upstream sequestration, minimizing slurrying and reducing costs. At
Scope/Content: Reservoir size: 7018 acre-feet. Height: 160 feet. Length: 620 feet.
Scope/Content: Date constructed: 1948.
Sediment and channel dynamics
Dam retirement
Matilija, CA
Matilija Dam

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