[Water_news] 5. DWR'S CALIFORNIA WATER NEWS: AGENCIES, PROGRAMS, PEOPLE - 6/6/07

Department of Water Resources

California Water News

A daily compilation of significant news articles and comment

 

June 6, 2007

 

5. Agencies, Programs, People

 

Perris dam quake work pegged at $460 million

Riverside Press Enterprise – 6/6/07

By Jennifer Bowles, staff writer

 

State engineers are proposing a nearly half-billion-dollar plan to retrofit the seismically weakened dam at Lake Perris, the Inland region's most popular lake, by shoring it up with a stability berm and adding an emergency channel to prevent widespread flooding.

 

Two years ago, engineers at the California Department of Water Resources discovered that the 2-mile-long earthen dam could crumble during an earthquake in the 7.5-magnitude range.

 

In a worst-case scenario, it could unleash 26 billion gallons of water across 30,000 acres of fast-growing western Riverside County, from rural Lakeview to the Prado Dam near Corona.

 

Lake Perris, wedged between the hills of Moreno Valley and Perris, was drawn down 25 feet to a safer level in the meantime.

 

The superintendent of Inland state parks said the impact to recreation while the repairs are being made will be significant.

 

Even though the lake will remain open during construction, the number of boats allowed at any one time will remain at 250, down from 450 when the lake is full. The lower number will be in effect until the dam is fixed, said Superintendent Gary Watts.

 

Preparation and repairs could take about three years to be completed. The lake attracts an estimated 1.2 million visitors a year.

 

Watts said the southeastern shoreline will be closed while the eastern end of the lake is excavated and sediment trucked to the construction site.

 

Although not as widely used as other parts of the lake, Watts said a picnic area and a trail leading to a popular rock-climbing area also will be closed. Waterfowl hunting in that area stopped when the lake was lowered.

 

The sound of bulldozers and rock blasting will disturb visitors boating and fishing in the lake, he said.

 

Watts said the California Department of Parks and Recreation, which runs Lake Perris as a recreation area, is expecting the state Department of Water Resources to make up for the loss of recreation by adding improvements such as new campgrounds and restrooms on the southeastern shoreline.

 

Stabilizing Berm

 

Under the plan, estimated to cost as much as $460 million, the dam's weakened foundation would be fortified and the so-called stability berm would nudge up against it, on the side opposite the lake, for added support.

 

In addition, a 2-mile-long emergency channel would run beside the adjacent Ramona Expressway so in a disaster large-scale water releases would be funneled away from the neighborhoods and into a storm drain.

 

Because the lake is used as a drinking-water reservoir, cost of the repairs would be divided among three Inland-area water agencies.

 

A magnitude-4.2 earthquake Friday night centered in the Coachella Valley rumbled through the area near Lake Perris. It was a stark reminder to some residents who can see the dam from their windows.

 

"I felt it, and of course I sat up in bed, and it was just very small but my chandelier in my bedroom was moving, and I thought 'Oh, my God, should I get my cats, the dog, what should I do, where do I go?' " said Jackie Burnip, 67, of Perris.

 

"It just really gave me a scare," she said.

 

Darren Madkin, assistant to the Perris city manager, said residents should remain prepared in the event of a disaster until the dam is fixed. An article in the city's last newsletter to residents suggested ways to prepare and said law enforcement and news-media outlets would let them know if they need to evacuate.

 

A map showed general directions of which way to evacuate but no specific routes.

 

"There's no telling where or when the failure will occur," Madkin said.

 

Emergency Channel

 

The dam repair plan issued by the water resources department, which owns and operates the structure, kicks off a year of analyzing the potential impact on the environment, traffic and other issues.

 

Teresa Sutliff, the agency's project coordinator, said that if all goes as expected, construction would begin in September 2008. She estimated it would take two years to work on the dam and its stability berm.

 

"Our No. 1 priority right now is to complete the dam first," Sutliff said.

 

The project would also include construction of a tower that funnels lake water into a regional drinking-water system to serve 18 million Southern Californians. The existing 105-foot-tall tower near the dam also has been found to be seismically weak, Sutliff said.

 

The dam itself would be fixed by removing the questionable foundation material and replacing it with blocks of soil-cement columns and recompacted fill. The stability berm would consist of about 2 million cubic yards of soil excavated from the dry lake bed at the eastern end, and 1 million tons of rock from the original rock quarry in the adjacent Bernasconi Hills.

 

The state will also evaluate placing the emergency-release channel through part of the fairgrounds and a motocross field before it heads to the Perris Valley Storm Drain. The existing emergency outlet has no channel to direct the water flow, so it could flow freely through downstream communities, according to the proposal.

 

At least one official from the three Southern California water agencies that must foot the repair bill questioned the cost and asked why the water suppliers are the only ones paying for it.

 

"We're not allowed to use it strictly as water storage. ... Lake Perris, for the most part, is operated as a recreational lake," said Steve Robbins, general manager of the Coachella Valley Water District. That agency would have to pay about one-third of the repair costs. Desert Water Agency in Palm Springs and Metropolitan Water District of Southern California would pick up the rest.  #

http://www.pe.com/localnews/environment/stories/PE_News_Local_B_dam06.424453b.html

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