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South Coast Reservoir Which Is Major Water Source Filling With Sediment

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The City of Santa Barbara's Gibraltar Reservoir had a maximum capacity of 14,000 acre feet, but sediment buildup has reduced it to a little over 5,000 acre feet

Tucked away on the Santa Ynez Mountains is a dam, and reservoir that’s been a key water source for a South Coast city for nearly a century, but one that’s now in trouble.

Gibraltar Dam was built in the early 1900’s, and has annually supplied about a third of the City of Santa Barbara’s water supply. Cathy Taylor, who’s is the City of Santa Barbara’s Water System Manager, says while Gibraltar has been hard hit by the drought, like other waterways in the region, it’s facing another big problem.

The water source is in trouble because of sediment from brush and forest fires in the region being swept into the reservoir by stormwater, literally taking away much of its storage capacity. What had been a 14,000 acre feet capacity is now down to just over 5,000 acre feet.

There’s no simple, and perhaps no economically feasible way to deal with the problem. Gibraltar is only about five miles north of Santa Barbara by air, but getting to it on roads in the Santa Ynez Mountains is much more difficult. Trying to dredge the reservoir would be a very expensive proposition, with some estimates in the $60 million dollar range.

She says the good news is that over the years, the city diversified its water sources, giving it many more options than just Gibraltar. There’s water from Lake Cachuma, groundwater, and water purchased from other water suppliers.

And, this year, the city’s revamped ocean water to fresh water desalination plant just went into operation. It currently has the potential to meet a third of the city’s annual water usage needs, but its modular construction allow it to be expanded to the point where it could meet all of the city’s usage at current rates.

It’s hard for the city to project how quickly the reservoir might fill to the point where it’s almost unusable, because the key factor is brush and forest fires in the backcountry which could then feed debris into waterways which drain into Gibraltar. Some debris dams have helped ease the sediment problem, but haven’t stopped it. And, Taylor says even if you did dredge, and remove the sediment filling the lake, it would be a continual process, because the next brush fire in the area would create more debris. It might be more practical to shift towards a larger role for other water sources, like the city’s newly revamped ocean water to drinking water desalination plant.

But, Taylor says as the city wrangles with questions like its future water supply, there is a lot of good news about the current situation. She says while the city is still in a drought situation, the community has responded to conserve in a big way. She says despite the city’s growth over the years, Santa Barbara’s water usage has dropped, and is at the same level now that it was at a half century ago, in the 1960’s.