Removing Matilija Dam:
About the Matilija Coalition:
Matilija Dam - Removal Alternatives:
page describes the initial alternatives screening process. The
alternatives were further refined during the study, and the preferred
alternative was selected based upon the habitat evaluation, cost,
environmental impacts, and other federal selection criteria.
Matilija Coalition matrix is our scoring for the various alternatives.
Overall ranking matrix shows each agency's total score and the overall average. The highest ranking alternatives are in green, lowest in red.
The four highest ranking alternatives (listed below) will most likely be carried forward for analysis during the next phase of the study:
Dam Removal/Natural Sediment Transport: Dam is completely removed
all at once with some sediment removal adjacent to dam for access
purposes. The majority of the deposited sediments would remain, for
natural transport downstream over time.
alternatives being considered are; Pool & Riffle System,
Partial Dam Removal/Full Sediment Removal, Partial Dam Removal/Natural
Sediment Transport, Full Fish Ladder/No Dam Removal, Restoration of
Dam, Fish Tunnel/ Bypass to North Fork Matilija. Each of these
options will be described along with a rationale for their elimination
in the Alternatives (F4) Report due for completion in June 2003.
Descriptions of sediment management alternatives:
1A- upstream stabilization: sediment will be moved to one side of the reservoir to create a new stream channel. Sediment to be stabilized using rip rap and revegetated.
1B - downstream transportation: sediment to be excavated from behind reservoir and trucked to downstream site and/or beaches
1BB - slurry pipeline: sediment to be excavated from behind reservoir and transported in slurry pipeline to downstream storage site and/or beaches
2- phased natural transport: dam to be "notched" in stages and sediment flushed by natural processes downstream
3- combination of alternatives 1 & 2: further study may determine that some combination of the above alternatives will provide the most cost effective and environmentally preferred method for dam removal
4 - Dam
removal with uncontrolled natural transport of sediment
In April, 2000, the Bureau of Reclamation completed an Appraisal Study that provided a preliminary evaluation of dam removal alternatives. While removal of the actual dam structure is straightforward, the technical challenges associated with handling the large quantity of impounded sediment will determine the ultimate cost and time scale for the project.
In this study, for each dam removal scenario the concrete dam will be demolished and removed to a recycling plant. The project will include a new high flow bypass diversion dam to replace the current structure at Robles (diverts river water to Lake Casitas).
The following alternatives reflect how the 6 million cubic yards of sediment will be handled. Note that the study eliminated single-phase removal and leave-in-place options because of their failure to accomplish project objectives.
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Page last updated: Oct 2002