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Statement of Purpose


Removing Matilija Dam:

Final Design:

Feasibility Study:

Early Progress:

Background Information:

About the Matilija Coalition:

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Matilija Dam - Removal Alternatives:

This 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.
A preliminary screening of the full range of alternatives was conducted. A total of 10 general concepts were ranked according to their effectiveness at accomplishing the key objectives of the study: restored habitat, fish passage, beach nourishment, and recreation. Also considered were relative cost and aesthetics. Each of the participating agencies submitted an alternatives ranking, and these were totaled and organized into a matrix.

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:

Full 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.
Full Dam Removal/Sediment Stabilization On-site: Remove entire dam. Stabilize some sediment in place; remainder of sediment placed in upland areas and stabilized. Re-establish stream channel using natural topographic gradient (unlike pool and riffle system).
Full Dam Removal/Mechanical Sediment Removal: Dam and sediment is completely removed in one phase. Mechanical transport of sediments to disposal site via trucking, helicopter, slurry, or conveyor. Disposal site may include beaches, landfill, agriculture, etc.
Incremental Dam Removal/Natural Sediment Transport: Dam is removed in segments (horizontal notching) in phases, over an extended period of time. The dam will act as a spillway allowing for sediment removal by natural transport as it is notched over time.

Other 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.

Sediment managment alternative
Approximate time
Estimated cost
1A upstream stabilization
2 years
$69.2 M
1B downstream transportation
4-5 years
$144.4 M
1BB slurry pipeline
4 years
$179.4 M
2 phased natural transport
25 years
$21.6 M
25 years $21.6 M
3 combination of alternatives 1 & 2

©Matilija Coalition, All Rights Reserved, 2002.
Page last updated: Oct 2002