Even though it’s rained more than normal across California, most of San Diego’s reservoirs are still not full. About 41 percent of the storage space in these artificial lakes remains empty.
Most of this is just the way things are in San Diego. Here, most of the region’s drinking water comes from the Colorado River and the melted snow of Northern California. Only about 5 percent of urban San Diego’s water comes from local rainfall.
Every time it rains big, people wonder what’s happening to keep it from wasting away into the ocean or whether their favorite lake is going to be full of water for fishing and boating. That’s all especially true this year. But even though it has rained more than normal, San Diego is not like other parts of the state, where many major dams are 80 percent full or more.
For one thing, the water that falls is the cheapest source available, so it’s the first sent to customers.
Now, San Diego’s biggest reservoir, San Vicente, is less than a tenth of the size of the state’s largest reservoir, Shasta Lake. San Vicente is about 77 percent full; Shasta is 96 percent full. This is what it means to live in a region as arid as San Diego.
There are 54 dams in San Diego County regulated by the state. Only about a dozen of them are plumbed to hold the imported water on which the region depends, and most are relatively small.
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Remember that the San Vicente reservoir is now over twice as large as it used to be, before the County Water Authority and the city spent millions of dollars raising the San Vicente Dam, so in fact, San Vicente Reservoir is now almost twice as full as in years past. The city chose to drain Lake Morena and send its water to downstream reservoirs. This article simply demonstrates that the author is not very aware of recent regional reservoir expansion and management practices.
San Vicente reservoir is probably the worst example you could have used in an article like this. The reservoir depends almost entirely on a San Diego Aqueduct pipeline delivering imported water from the Colorado River and Northern California. San Vicente's insignificant watershed constitutes only a small fraction of its water supply, so rainfall is almost completely irrelevant as a source of water there.
If you intend to discuss the connection between local reservoir levels and weather conditions, I'd say you need to ignore reservoirs that are fed solely or primarily with imported water (Miramar and Murray are two other examples).
(I acknowledge that Morena was mentioned, but it's unique in being quite shallow and wide and subject to excessive evaporation, more so than typical area reservoirs, so the City of San Diego is loath to leave water there to evaporate away, which is why they send it down to the Lower Otay Reservoir that's deeper and has a more reasonable evaporation rate. And Morena is subject to politically motivated withdrawals too, but that's another story.)
I don't buy consumption as a relevant factor, because conservation has been a big success in San Diego and if anything that contributes to higher, not lower, reservoir levels. And what does consumption have to do with how much rainfall ends up in reservoirs, anyway?
The story does mention two relevant possible reasons why the rain didn't fill up our reservoirs, although they are pretty obvious to most of us anyway: 1) there's a good chance a lot of the rainfall was absorbed in the soil instead of running off into the reservoirs, and 2) some watersheds may not have received more rain than others.
A third reason might be that it takes several years in succession of good wet winters to get our natural reservoirs full.
@George J. Janczyn Otay reservoir is also supplied mainly with imported water.
Otay does receive imported water but I didn't point it out because it also receives a substantial amount of water from its watershed.
@George J. Janczyn --The vast majority comes from the 2nd San Diego Aqueduct.
Okay, I won't argue that point. My main point was that reservoirs filled primarily with imported water shouldn't be used as examples in explaining why local rainfall hasn't raised reservoir levels.
@George J. Janczyn George,
Thanks for the comment. A few things: I tried to hit all or almost all of these points: that only 5 percent of our water comes from rainfall; listed the different above-average rainfall percentages in three different regions of the county (though didn’t explicitly say this means some watersheds and thus reservoirs have less water than others); and said that “water was absorbed by the ground.” I did ask both CWA and PUD for the ratio of local to imported water in the system as a whole and within some reservoirs in particular, and they said they couldn’t provide that right now, which in retrospect maybe I should have pushed a bit harder to get to address the points you make.
I did struggle with which to use as an example and you make a good point about San Vicente, but El Capitan has a fill restriction that may complicated things (PUD seems to be taking as much water as they can out of El Capitan) and Morena has some complications you mention, plus seems to be bordered by a groundwater basin that is sucking up water before it reaches the lake. Murray and Miramar may the most sense, but they are also so small, I tried to hit two points at once: relative size and relative %, so I went with San Vicente.
Thanks, Ry for explaining the difficulty in writing this up. I do sympathize with the trouble you encounter in obtaining information from our water agencies. When I was water blogging I recall times when I couldn't get timely information from San Diego's Public Utilities Department because the mayor required that responses to queries had to first be cleared through his office (that was before Mayor Faulconer, I'm not sure how it works now).
@George J. Janczyn To be clear, that was not a problem in this instance: PUD just did not have the information on hand. They were generous with their time -- the spokesperson for the agency, a deputy director and an assistant director helped, this was just not information they had readily available.
"One of the biggest fears is that an earthquake will cut San Diego off from Metropolitan’s system, leaving the county to fend for itself until pipelines can be repaired. The Water Authority stores enough water in the county to be entirely cut off for two months."
Is only two months adequate? From a 2014 story in the Los Angeles Times, it could take more than year to get all of the aqueducts fully back in service following a major rupture on the San Andreas.
"If nothing is done, Southern California could be left with less than six months of stored water on the L.A. side of the San Andreas fault. It could take more than a year to get all three aqueducts flowing again after a major quake."
@Greg Martin This, like George's comment above, is also astute: The Emergency Storage Project, as the Water Authority's program is known, has two time frames: One is to ensure that service can be provided at 75% normal levels for two months “in the event of a complete interruption” of water deliveries from Metropolitan. The second is to provide similarly reduced service for six full months “in the event that a limited amount of water was available” from Metropolitan. (see http://www.sdcwa.org/sites/default/files/files/finance-investor/longtermDebt/2015A_OS.pdf at pg. 54)
To be frank, the Water Authority often uses language like "up to six months" for the region -- and until I was reporting this article I didn't realize that the emergency plan is for two months of local storage in the nightmare scenario of being entirely cut off from Metropolitan. That said, the city has its own emergency plan, which requires it to have 7.2 months of storage on hand for city customers at all times (see https://www.sandiego.gov/sites/default/files/2015_uwmp_report.pdf at pg. F-20).