San Gabriel Valley reservoirs' capacity reduced by sediment from recent forest fires
PICO RIVERA - The mud and debris that poured down the fire-charred slopes of the Angeles National Forest following the rains earlier this year continue to cause headaches for the county's Department of Public Works.
After facing the danger such mudslides pose to foothill homes, the department is now dealing with their threat to the region's water supply.
Much of that sediment ended up in the region's reservoirs, and will continue to end up there, in such large amounts that the reservoirs' capacity will be significantly reduced in the coming years.
"The combined effect of all the Southern California wildfires in recent years, not just last year's fires, has had a devastating impact on our water supply," Director of Public Works Gail Farber said Monday at an event commemorating Water Awareness Month.
The reservoirs store local rainwater and melted snowfall until some of it can be released to spreading ponds to seep into the underground aquifer for later use as groundwater.
Farber estimates that more than 10 million cubic yards of sediment - an amount that would fill 1 million dump trucks - will have to be removed from county reservoirs and catch basins over the next five years to maintain their current ability to conserve water and keep it from being wasted to the ocean.
Figuring out where that massive amount of mud and sand can go, and who will pay for its removal, is presenting a challenge for public works officials, according to Mark Pestrella, deputy director of the Department of Public Works.
The department regularly removes sediment buildup from county reservoirs, and has a 20-year management plan to do so.
But the massive quantities of sediment that have resulted from the fires and subsequent rains means that the department will have to do in five years what it had planned to do in 20 years.
The Station, Morris, and Sayre fires "dramatically accelerated our expected sediment load and drastically reduced our capacity of our reservoirs," Farber said.
The fires destroyed vegetation that helps keep soil in place and directs rainwater into the soil. So now when it rains, water rushes down the charred slopes, taking soil with it.
Under natural conditions, that extra sediment would have made its way to the ocean, re-nourishing beaches and leaving sand deposits along the way, Pestrella said.
But with man-made channels and dams replacing the natural system, the sediment has to be moved mechanically, a costly endeavor.
The department spent more than $30 million on rental trucks alone this year to remove 1.2 million cubic yards of sediment from debris basins aimed at keeping mud and debris from flowing into foothill homes, Pestrella said.
By comparison, from 2005 to 2008, the county spent an average of about $2 million annually on debris basin cleanup.
And the cost of removing sediment over the next five years is expected to reach at least $112 million. That expense could be shared by water agencies and the communities that benefit from the water storage capacity at reservoirs, Pestrella said.
The Federal Emergency Management Agency and the California Emergency Management Agency announced Monday that some of the cost of debris removal could be recouped from federal and state grants.
Where the abundant sediment goes is another question.
So far it has been moved to county properties, but those are rapidly filling. Now public works officials are trying to find creative places for sediment placement in the coming years.
Pestrella says the sediment can be useful, as construction aggregate, filling in old gravel pits, in development projects, and, possibly, for beach replenishment.
He recognizes that the last use can be highly controversial among environmentalists. This summer, the department plans to hold a series of public workshops to come up with the "best possible solution" of how to manage the "incredible sediment load," Pestrella said.
The department will hold an initial meeting Thursday at 7 p.m. to discuss, among other things, debris removal from La Crescenta and its impact on the community at the community's Center for Spiritual Living, 4845 Dunsmore Ave.
"We believe we can maintain our water supply system in place, but we need to act now and move this sediment," Pestrella said.
Source: http://www.pasadenastarnews.com/news/ci_15057539--
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