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Water Supply Availability |
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Thursday, 13 November 2008 |
WATER SUPPLY AVAILABILITY
| New storage reservoirs, both above ground and underground, are needed to store more water for the future. At the same time, the current system of conveyance canals and pipelines must be improved to deliver this increased supply of water to water users. |
A review of the following information from the 2005 California Water Plan, produced by the California Department of Water Resources, reveals that in most years water is available that is not already dedicated to a specific use. During normal and dry years, the total water supply is double the dedicated use. That number increases to four times the dedicated use during wet years. It is a portion of this undedicated water supply that will help improve California’s water supply.  In average water years like 2000, California receives about 200 million acre-feet of water from precipitation and imports from Colorado, Oregon, and Mexico. Of this total supply, about 50 to 60 percent is either used by native vegetation, evaporates to the atmosphere, provides some of the water for agricultural crops and managed wetlands (effective precipitation), or flows to Oregon, Nevada, the Pacific Ocean, and salt sinks like saline groundwater aquifers and Salton Sea. The remaining 40 to 50 percent (denoted as dedicated supply) is distributed among urban and agricultural uses, used to protect and restore the environment, or stored in surface and groundwater reservoirs for later use. In any year some of the dedicated supply includes water that is used multiple times (reuse) and water stored from previous years. Ultimately, about a third of the dedicated supply flows to the Pacific Ocean (in part to meet environmental requirements) or to other salt sinks. Statewide, local surface water and groundwater supplies make up about 50 percent of California’s total dedicated supply in an average water year (percentage varies regionally). Water also moves great distances in California within and between its 10 hydrological regions. In wet and drier years, like 1998 and 2001, respectively, the total supply and the distribution of the dedicated supply to various uses differ significantly from the example above for an average year.
California Water Summary, (maf)
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1998
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2000
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2001
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(117% of normal) (a)
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(97% of normal)
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(72% of normal)
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Total supply (precipitation & imports)
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336.9
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194.7
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145.5
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Total uses, outflows, & evaporation
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331.5
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200.4
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159.9
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Net storage changes in state
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5.5
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-5.7
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-14.3
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Distribution of dedicated supply (includes reuse) to various applied water uses
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1998
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2000
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2001
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| Urban uses |
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7.8 (8%)
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8.9 (11%)
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8.6 (13%)
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| Agricultural uses |
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27.3 (29%)
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34.2 (41%)
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33.7 (52%)
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| Environmental water (b) |
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59.4 (63%)
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39.4 (48%)
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22.5 (35%)
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Total dedicated supply 94.5 82.5 64.8
maf = million acre-feet
a. Percent of normal precipitation. Water year 1998 represents a wet year; 2000, average water year; 2001, drier water year.
b. Environmental water includes instream flows, wild and scenic flows, required Delta outflow, and managed wetlands water use. Some environmental water is reused by agricultural and urban water users.
Source: California Water Plan, Bulletin 160-05; California Department of Water Resources
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WSA 
