Tuesday, December 18, 2012

Matilija Dam 2012 update

Matilija Design Oversight Group (DOG) Meeting - Dec 4 9am - noon

The Matilija Dam 'Design Oversight Group' met on December 4th.  Presentations updated the group on the Corps process and progress on elements of the final design.  this was followed by a discussion and approval of the Technical Advisory Committee work plan for 2013.

The main progress is the recent design study for the Santa Ana bridge. An assessment determined that an upstream alignment for a new bridge will be the best alternative for the Santa Ana Rd crossing in Oak View.

This presentation as well as a presentation on the giant reed removal may be downloaded from matilijadam.org

Next Steps:

Over the past year, the Matilija Dam Technical Advisory Committee (TAC) has completed a draft work plan for the next steps in resolving the issues with removing Matilija Dam.  This report will be presented for approval by the DOG.  The final document will be used in a Request For Proposals (RFP) to go out to consultants early 2013.  The California Coastal Conservancy plans to sponsor additional studies recommended by the TAC as follows:

Task 1: Dam Removal Plans
The goal of this study will be to formulate feasible methods for the removal of Matilija Dam, located on Matilija Creek in Ventura County, California. The study will develop the engineering details associated with several different alternatives for mechanical sediment management and flow control during dam removal. This study would not evaluate the downstream slurry options, but would focus on the mechanical placement of sediment upstream of the dam and evaluate options for the control of flow and sediment during dam removal.  The study will be performed in two phases, with the first study done at primarily a conceptual level and the second study done in more detail on a fewer number of options to develop more reliable costs and impacts for those options.

The analyses will examine approaches for Full Dam Removal as well as an Interim Notch.  The Interim Notch would have the main purpose of preventing further deposition in the reservoir area, but could also have the additional purposes of inducing a small amount of erosion so that the sediment removal process could begin and providing data on the sediment processes that would occur upon dam removal.

Task 2: Sediment Analysis of interim and dam removal schemes
The goal of this study will be to simulate the sediment transport processes for the proposed interim notching and full removal schemes that will be evaluated in dam removal plans (Task 1).

Task 3: Robles Diversion Mitigation
The removal of Matilija Dam Removal has the potential to increase the sediment concentration within Matilija Creek and the Ventura River downstream of the dam during and after the removal process. This scope of work would develop methods to mitigate the impact to water supply through supplying water of acceptable quality during the period of impact. This study would be done in close collaboration with Task 1 and 2 (1: Dam Removal Plans 2: Erosion and Sediment Transport Modeling Analysis and). Task 2 will determine the potential for lost diversion opportunity at Robles as well as the magnitude and duration of lost diversion opportunity by computing the duration and seasonal timing when diversions will be precluded by high turbidities. The magnitude and duration of lost diversion opportunity will guide the water loss mitigation analysis

The completed TAC reports may also be downloaded at matilijadam.org

More on the recent history of the project on this blog:  Matilija Dam