A recent Ventura County grand jury report lists the Westlake and Lake Sherwood dams as two of the 14 dams in the region that could have a “significant impact” on residents if the structures were to fail. Ten of the dams are in Ventura County and four in Los Angeles County.
The 2017-2018 grand jury report was commissioned in light of last year’s major destruction at Oroville Dam in Northern California during the strong winter storms. The grand jury investigated 20 dams in Ventura County and surrounding areas and found that more than a dozen could lead to a major loss of life and property if they failed.
In Ventura County, the state rated Castaic, Bouquet Canyon and Santa Felicia dams as “fair” and Matilija Dam as “poor.”
The report is not as bad as it sounds, said a spokesperson for the Las Virgenes Municipal Water District, which is the owner and operator of the dam that fronts Las Virgenes Reservoir in the hills above the Three Springs neighborhood of Westlake Village, also known as Westlake Dam.
“I think (Westlake) was included in the grand jury report because it is a dam where there’s a large population surrounding the dam area. (The grand jury) kind of wanted to suggest that they’re on top of looking at where these dams are located,” LVMWD’S Mike McNutt said.
Four of the area dams had “existing or potential deficiencies,” the report said. Westlake and Lake Sherwood are not among those that are structurally compromised.
“We have no deficiencies regarding the structure or integrity of both (Westlake) dam and the reservoir,” McNutt said.
“In fact, when the dam was constructed it was built directly on top of bedrock, which increases the strength and ability to withstand seismic activity. (Las Virgenes water district) took those extra precautions to ensure that downstream residents are safe,” he said.
Bad history
Ninety years ago the St. Francis Dam collapsed on a tributary of the Santa Clara River in Ventura County, letting loose approximately
12.4 billion gallons of water and creating a wall of water two miles wide as the river surged 54 miles to the Pacific Ocean.
St. Francis hasn’t been the state’s only dam to fail.
“As a result of the failure at the Oroville Dam spillway, California officials ordered new and more detailed inspections of approximately 100 dams within the state,” the grand jury report said.
Also in the wake of last year’s Oroville disaster, the California Division of Safety of Dams issued a report on all 1,249 dams under its jurisdiction and gave the Westlake dam a satisfactory rating, the highest level under the statewide evaluation system.
In the 2017 report, the state classified the dam’s downstream flooding hazard as “extremely high” but, again, the alert was due to the presence of homes in the area, not the condition of the dam itself, the Las Virgenes district said in a statement.
The recent report by the county grand jury recommends the state Office of Emergency Services consider working with the dam owners and cities to develop and distribute dam failure inundation maps and other information to assist residents in planning for the possibility of structural failures.
May 30, 2018
The Acorn
By John Loesing
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