Thursday, September 27, 2018

Hidden costs of Matilija Dam

A headline in the Ventura County Star states:

Thousands of residents live in homes protected by a levee that stretches 2.65 miles along the Ventura River, between the Pacific Ocean and Shell Road.

In the more than 3,500 residential, commercial and industrial structures lie an estimated $2.157 billion worth of infrastructure and property, according to studies prepared for the Ventura County government.

Experts with the U.S. Army Corps of Engineers say that without rehabilitation, it’s likely the levee could in time breach or collapse entirely. 

When the initial levee was built in 1948, one thing not considered was the loss of sediment likely to result from construction of Matilija Dam, which had been installed on a major tributary only the year before, the corps noted.

“Basically, the foundation of the levee is higher than the potential bottom of the river,” said Paul Jenkin, Ventura County campaign coordinator for the Surfrider Foundation.

That means in a flood or high-rain event, the river could flow under the base of the levee, causing it to fail. The change has been notable. Initially, the levee was made with 8 feet of toedown, which means rocks extended that far below where the riverbed meets the base of the levee. Today, there is “minimal to no toedown protection,” the corps noted.

Poorly understood at the time the dam was built, these are the long-term costs of a sediment starved river.

Although the $25 million Ventura River Levee VR-1 project is not included as part of the Matilija Dam ecosystem restoration project, three other levees are.  The bulk of the planning and removal costs of dam removal involve the replacement, upgrade, or new infrastructure downstream of the dam to accommodate the restoration of the Ventura River's natural sediment transport.


Ventura River Levee Project (VCWPD VR-1, FEMA ID No. 53)