OJAI, California -- Civil engineers planning the demolition of the 60-year-old Matilija Dam on the Ventura River are enjoying an unprecedented preview of where 163 million gallons of pent up water will flow, thanks to sophisticated new computer modeling techniques now being used for a series of dam removal projects planned throughout the United States.
"Years ago we thought, we'll just take the dams out and see what happens," says Rod Wittler of the U.S. Bureau of Reclamation. "We're learning how to think it through. We haven't taken any large, large dams down and that's why we're so dependent on computer modeling to tell us how to make this work."
Dam removal plans have proliferated in recent years, as evidence mounts that many dams are not only obsolete, but have hindered or blocked natural processes, including bringing sand to beaches and allowing fish to reproduce. Plans to remove the Matilija Dam have been in the works since the late 1990s, but planners have struggled with the best method of demolishing the structure without damaging life and property downstream.
The computer modeling is making that easier, and enabling engineers to start building levees, bridges and footings ahead of the rush of water and silt, instead of waiting to see where things land and trying to sort out any damage afterwards. Modeling also lets planners protect historic buildings and keep invasive species of plants from spreading with the mud.
"We’re working to anticipate the effects of bringing down a dam this size for many miles downstream as well as on the immediate habitat area," says Doug Chitwood, the U.S. Army Corps of Engineers project manager for the removal. "It’s taken years of study to understand impacts that weren't even imagined at the outset of the project."
Engineers first sent up an airplane equipped with light detection and ranging, or LIDAR, gear, which uses lasers to capture detailed terrestrial data. They turned the data into two digital maps: a one dimensional cross-section map sampled at every tenth of a mile, and a two-dimensional map in 10-foot to 20-foot increments.
To predict the flow of water and silt over that digital terrain, scientists turned to the work of Hans Albert Einstein, the first son of physicist Albert Einstein, who made key advances in sediment transport theory while an engineering professor at the University of California in the 1940s.
"He was a major player in modeling sediment movement and we still use his models, but in computers," says Blair Greimann, who's led the modeling efforts at the Bureau of Reclamation.
The resulting model shows where the water is expected to go, both during the first rush and as the river settles down; and various scenarios for where a mountain of sediment held behind the dam could end up.
The Matilija Dam was built in 1947 on the Ventura River, about 16 miles inland and uphill from the city of Ventura, to provide a reservoir of water for farming and urban use. The dam's effect on the river downstream effectively ended the steelhead trout's spawning trips upstream -- much like salmon -- and cut the supply of fine sediment that ends up as sand on the ocean beaches at the river's mouth.
Like many dams, Matilija's uselessness became apparent by 1964, but developers continued to build bridges, roads and homes that assumed it would remain in place. It holds back just 500 acre-feet of water, enough for 500 households for a year. But it's loaded with silt, which complicates the demolition.
"There are 6 million cubic yards of sediment behind that dam, a football field filled 3,000 feet high," says Greimann. "We're trying to avoid the California mudslide effect."
Experts are closely watching the Matilija Dam demolition project to see what they can learn and do better, especially with dams in more densely populated areas where wayward water could effect more than plant life. Several other big dams, including the Klamath River dams in California and Oregon, are being studied for removal sometime after the Matilija demolition, which is expected to take place in 2010.
In April, an Oregon State University symposium on modeling dams held the first conferences on dam removal to try to formalize the science behind modeling.
Based on the modeling, civil engineers have mounted nearly a dozen construction projects tied to the river's predicted course. Theresa Stevens, an environmental project manager with the Ventura County Watershed Protection District says the money for the projects is being secured and they're underway.
"We calculate that we need to do 12 capital improvement projects, the 12th being blowing up the dam," Stevens says.
The USBR's hydraulic simulation tool is in the public domain, and can be downloaded from the agency's website. It works with geographic information software called ArcGIS.