Gibraltar Reservoir Poised to Spill

Overflow Will Run Downstream into Lake Cachuma

Gibraltar Dam
Paul Wellman (file)

With the recent dumping by three successive storm cells, the City of Santa Barbara’s Gibraltar Reservoir is poised to spill, meaning runoff water should soon start pouring downstream and into Lake Cachuma in significant quantities for the first time since 2011.

As of Tuesday evening, Gibraltar — by far the smaller of the two reservoirs from which the city draws — is about two feet from spillage, meaning it could overflow anytime. With Gibraltar overflowing, all the water it had previously short-stopped — thick with sediment from recent fires — can now run towards Cachuma, which is reportedly 11 percent full. Last week, it was at nine percent of storage capacity.

Once Gibraltar spills, Cachuma can impound inflow and runoff at a much faster rate. But as usual with this year’s rains, the news looks rosier than it immediately is. First, the most recent storm proved substantially less bountiful than predicted. Second, none of the water flowing into Cachuma can be used by the member water agencies drawing from the dam until there’s a live stream flowing from the base of Cachuma down the main stem of the Santa Ynez to the ocean. Even then — according to byzantine water accounting rules — another 4,000 acre-feet worth of water will have to be set aside for downstream users, and another 2,000 acre-feet set-aside to replenish accounts created for steelhead restoration efforts, before South Coast water agencies can start availing themselves to the accumulated run-off now collecting in Cachuma.

Since this year’s rains, about 5,000 acre-feet have accumulated in Lake Cachuma. “Lake Cachuma was a lot better off last year at this time than it is now,” said city water Czar Joshua Haggmark. “We still have a long way to go.” Haggmark said the drought won’t be officially over until Cachuma spills again. If it fills halfway, he said, the city might consider rolling back the lawn watering ban and other drought inspired restrictions.

Haggmark noted that about half the watershed that feeds Cachuma has to go past the pinch point of Gibraltar first. Imagine a land mass ten times the size of the City of Santa Barbara feeding into Gibraltar. Once the water starts moving, Haggmark said, “It gets pretty explosive.” Haggmark expressed both chagrin and relief that the heavier rains passed the city by. “I hate to be the guy who says, ‘’Where’s my three inches?’ But where are my three inches?” But had the rains hit much harder, he cautioned, they could have inflicted a lot more damage given how parched and splashy the landscape is.

In the meantime, Haggmark and other South Coast water managers are scrambling to save 30,000 acre-feet of state water they stored in the San Luis Reservoir by Los Banos, now approaching capacity. Once that happens, all water banked there is lost. Santa Barbara agencies are pursuing a possible deal with the Metropolitan Water District in which the Santa Barbara agencies give MWD three acre-feet for every two acre-feet MWD provides.

Haggmark, meanwhile, said there’s no rain forecast for the next ten days. “Anything beyond that is strictly Voodoo.” After the rainy season runs its course — usually sometime in March — local agencies will have a better idea how to proceed. Even though Santa Barbara County has received far more than average rainfall this year, federal forecasters continue to predict less than average precipitation.

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