The Santa Clara Valley Water District confirmed
– in the form of a capital project proposal – the worries that
arose in 2009: if a large earthquake hits within 1.25 miles of
Anderson Dam, downtown Morgan Hill will be underwater within 15
minutes. The independent seismic study conducted two years ago set
the water district into motion Wednesda
y with the announcement that the 60-year-old dam will be
retrofitted at the estimated cost of $110 million. Construction is
set to begin in 2015. Keep reading to find out what locals think
about the possible failure or Anderson Dam.
The Santa Clara Valley Water District confirmed – in the form of a capital project proposal – the worries that arose in 2009: if a large earthquake hits within 1.25 miles of Anderson Dam, downtown Morgan Hill will be underwater within 15 minutes. The independent seismic study conducted two years ago set the water district into motion Wednesday with the announcement that the 60-year-old dam will be retrofitted at the estimated cost of $110 million. Construction is set to begin in 2015.
Spokesman Marty Grimes said the seismic retrofit is “an extremely important project that we simply must do. The study answered questions about the seismic stability of the dam, but the capital project is just starting the planning phase, so there’s a lot that is yet to be determined in terms of the solutions, cost and impacts.”
In 2009, the California Division of Safety of Dams banned Anderson Reservoir from keeping a water level more than 74 percent, because the dam’s foundation contains sand and gravel that could liquefy in a big quake.
Though the water district doesn’t have an estimate now, the money for the three-year project will be funded by groundwater production charges, according to Grimes. It’s estimated that in fiscal year 2012 that began July 1, South County’s rate payers will generate $9.3 million in revenue while the cost to maintain wells, reservoirs, improve infrastructure is about $16.8 million a year.
According to the district, the project will likely be paid for by a combination of pay-as-you-go funding, debt proceeds and reserves. The exact parceling of those funds is unknown. South County’s portion of the water district’s budget is facing a deficit until fiscal year 2014 and typically for capital improvement projects South County funds capital costs after a project is completed. North County fronts the money and South County repays with interest after it’s completed. The district has budgeted $6.9 million for the retrofit so far.
“We will look at other potential funding sources such as state and federal grants and/or a special parcel tax,” Grimes said. He did say the water district will also pursue grants.
The analysis released Wednesday did provide an upside to the lake’s visitors this boating and fishing season. The water storage restriction at Anderson has been lowered to 57 percent capacity since October 2010 and can now be safely adjusted according to the California Division of Safety of Dams and the federal Energy Regulatory Commission to allow 12 more feet of water, up to 68 percent of capacity.
In October the publicly funded wholesale water provider to most of Santa Clara County, received preliminary findings from an ongoing seismic stability evaluation for Anderson Dam that detailed part of the dam could experience “significant slumping” if a 7.2 magnitude earthquake were to occur on the Calaveras Fault within about a mile of the dam. That spurred the reduction of the water level to 20 feet below the crest.
“This is not a discretionary project. Since we now know we have a deficiency, we need to complete the retrofit to protect public safety. We also need to restore the lost water supply capacity due to the operating restriction,” Grimes said.
An earthquake geologist from the U.S. Geological Survey said the probability of a quake 6.7-magnitude or larger in the next 30 years anywhere on the southern portion of the Calaveras fault – where Anderson Dam is located – is less than 1 percent. The study claims that if the dam did fail Morgan Hill will be hit with a 35-foot wall of water and floodwaters will reach Gilroy in 2.5 hours.
The anticipated start date for construction is 2015 with expected completion by 2018. Work on the actual plan and design for the retrofit have not begun, but the water district says the dam will need to be modified, rather than replaced, to strengthen it so it can withstand the “maximum credible earthquake” or a 7.2 quake. “It will likely involve removing some of the liquefiable material and adding additional rock to physically widen the dam,” Grimes said.
The need for construction evolved from updated seismic standards and the fact that Anderson Dam – along with seven other water district run reservoirs – haven’t been evaluated against the current standards. The dam safety regulators along with the water district “agreed that the study was necessary to protect public safety. The district’s top priority is public safety. Though the probability of a dam failure occurring is low, the consequences of failure are extremely high,” Grimes said.
A planning study will evaluate the adequacy of the outlet works and spillway, which was not part of the seismic dam study. Grimes said that if the outlet and/or spillway need to modified or replaced, the cost of the project will likely increase.
“We won’t have a good cost estimate until the planning study is completed,” Grimes said.
During the planning process, the district will develop “feasible alternatives” that will require changes to the reservoir so construction work can proceed; the degree and duration is unknown at this point. Construction could take two to three seasons, because both the upstream and downstream parts of the dam need to be fixed. It’s unknown now if the water level at Anderson will be too low for recreation or if it will have to be drained during construction.
For nearby Coyote Reservoir and dam, the retrofit at Anderson on East Cochrane Road won’t likely experience any serious impacts except the possibility of allowing more recreation at Coyote during the construction, especially if water levels are lowered at Anderson. It would have to be coordinated with Santa Clara County Parks and Recreation, however, during the planning and design phases.
The water district estimated four to seven jobs will be created for every $1 million spent on consultant contracts, and 10 to 20 jobs per $1 million of construction contracts. At Anderson, $20 million is planned for consultant contracts (80 to 140 jobs) and $90 million for construction, 900 to 1,800 jobs.
The water district provides water supply and flood protection to Santa Clara County’s 1.8 million people. The government agency employs about 750 people and manages an annual budget of $312 million.
A Morgan Hill Times intern wandered downtown Morgan Hill Friday morning and interviewed various people concerning recent developments surrounding the state of Anderson Dam.
“How fearful are you of a 7.2 magnitude earthquake hitting within 1.2 miles of Anderson Reservoir resulting in the failure of the dam and flooding Morgan Hill?”
Here are the responses:
“I’m not too worried because it’s not like the ocean, it’s only a lake, so it wouldn’t do too much damage if it broke. It wouldn’t be like a tsunami,” said Billy Ngan, 46 of Morgan Hill, an employee of Main St. Bagel & Co.
“I don’t think that it would break in an earthquake. It’s stood for 60 years, and it seems structurally sound. Of course it’s important to be prepared, to maintain it. We must be proactive, as with this plan for renovation,” said Maria Nash, 42 of Morgan Hill, a technical recruiter.
“It’s important to reinforce it in order to keep people safe. I am afraid that without these reinforcements, the dam would probably break in an earthquake and flood Morgan Hill. At that point it would be too late to do anything about it, so it’s good that they’re taking action now,” said Jesus Arrelo, 54 of Morgan Hill, a truck driver.
