Happy Birthday, Yosemite! Happy New (Water) Year!
How happy will they be?
Happy 125th birthday to Yosemite. We plan to celebrate by demonstrating in court that Hetch Hetchy is more valuable as a valley than as a reservoir.
October 1 also is New Year's Day - if you are a hydrologist. Water Year 2016 runs from October 2015 through September 2016. It makes sense to define "water years" in such a way in California where almost all of the rain and snow falls between November and May.
With strong El Niño conditions in the eastern Pacific, it's hard not to be optimistic that 2016 will bring welcome relief to California's severe 4-year drought. While we opined in the Sacramento Bee last month that our water systems need, more than anything else, long term improvements in groundwater recharge in wet years, it would obviously be wonderful to see our principal surface reservoirs fill.
But how much water does it take to fill these reservoirs? And how likely is it that a wet year will provide enough runoff to do so?
California's largest reservoirs are in the Sierra Nevada. The likelihood of refill varies considerably, depending on the size of each river relative to its principal reservoir, as well as numerous other factors.
Figure 1 shows how the volume of flow has varied over a 94 year period from 1922-2015 on eight large rivers in the Sierra Nevada - from the Sacramento in the north to the San Joaquin in the south. For each river, 5 levels of hydrology are shown. A 10% (Very Dry) hydrology means 90% of years are wetter; a 25% (Dry) hydrology means 75% of years are wetter; and so on. All volumes are measured in thousands of acre-feet.
In addition, Figure 1 also shows the maximum capacity of the principal storage reservoir on each river as well as the current amount of water now being held. Four of these reservoirs - Folsom, New Melones, Exchequer and Millerton - are very close to empty.
While all the rivers, as well as the water systems they serve, are different, it is easy to see that precipitation in a single wet year is far more likely to refill surface reservoirs on some rivers than on others. On the Sacramento, Yuba, American and San Joaquin Rivers, it is highly likely that a wet year will fill Shasta, New Bullards Bar, Folsom and Millerton Reservoirs. It is much less likely that storms in 2016 will refill New Melones Reservoir on the Stanislaus River or Exchequer Reservoir on the Merced River.
The likelihood of refilling the Feather River's Oroville Reservoir lies somewhere in-between. Oroville is the primary storage facility for the State Water Project, on which most California cities rely for at least some of their supply.
The likelihood of refilling storage of Don Pedro Reservoir on the Tuolumne River also lies somewhere in the middle. San Francisco's Hetch Hetchy Reservoir lies upstream and is more than 75% full. On the other hand, San Francisco's water bank in Don Pedro Reservoir - which can hold twice as much as Hetch Hetchy Reservoir - is less than 25% full. For a description of how runoff on the Tuolumne gets divided between San Francisco and the Turlock and Modesto Irrigation Districts see "Our Cattywampus Water Rights".
Reports and analysis done by Restore Hetch Hetchy and others, which show that restoration can be accomplished without anyone losing a drop of water, have all analyzed how an improved system would perform during drought years. That is how water planning works. We look forward to sharing these studies in a court of law as we show that Hetch Hetchy is more valuable as a valley than as a water tank.
Please consider providing financial support for our lawsuit as it moves through the legal system. It is time to make Yosemite National Park whole once again.