‘Show Me The Water' guidebook issued for suppliers By Khaled M. Bali
Thursday, November 6, 2003 2:33 PM PST
Irrigation/water development adviser
California Department of Water resources issued the "Show Me The Water" guidebook last month for Senate Bill 610 and Senate Bill 221 to assist water suppliers, cities and counties in integrating water and land use planning. The bills were effective Jan. 1, 2002, and require that approvals of large new developments be linked to assurances that there is an adequate water supply. Prior to the legislation, large projects could be approved without a demonstrated water supply. The new guidebook provides a foundation for developing comprehensive water plans and policies to meet the future water needs for the state.
These bills are examples of good efforts being developed to address many water challenges facing California. The quantity of water available for Californians has not increased over the past five to 10 years while the population continued to increase. Most of the demand was met by increased water-use efficiency, recycling of water and agricultural-urban water transfer programs. Most of the water that will be available to urban users in the near future will come from improved agricultural productivity and water-use efficiency.
In the long run, most of the water that will be available to meet the expected increase in population will come from recycling of municipal water, urban water-use efficiency measures, desalination, water quality protection and other measures. Agriculture-to-urban water transfer plans will play a major role in meeting the expected demand for more water. Despite the statewide aggressive agricultural water-use efficiency measures that have been implemented over the past 10 to 15 years, we have not and may not see any substantial increase in irrigated acreage in California. Growers in California will continue to improve water-use efficiency and increase productivity and most of the saved water will be transferred to urban users. Tailwater or runoff recovery systems and drip or low-volume irrigation systems are examples of the measures used locally to improve water-use efficiency.
Where is the water?
California's main water sources are either surface sources such as rivers and creeks or groundwater sources. California has a wide range of climatic zones with average annual precipitation ranging from 51 inches in the North Coast region to 5.5 inches in the Colorado River region. The average statewide precipitation in a normal year is about 23 inches. Almost two-thirds of this water is used by native vegetation, evaporation and groundwater storage. About 80 percent of the natural runoff occurs north of Sacramento, while 80 percent of the demand is south of Sacramento. The uneven distribution of runoff water is due to the various climatic zones in the state.
There are 10 hydrologic regions in California. The Colorado River region includes Imperial County, the central and east part of Riverside County, the east part of San Diego County and the southern part of San Bernardino County. The average annual runoff in the Colorado River region is .2 million acre-feet and the average annual precipitation is 5.5 inches (1 acre-foot is about 326,000 gallons of water). Natural runoff and precipitation in our region are the lowest among the 10 hydrologic regions in the state.
Colorado River water is an example of a surface source that is originated in other Western states. The river is used in seven states and Mexico. The state's share from the Colorado River is 4.4 million acre-feet. However, California has been able to use about 5.2 million acre-feet of Colorado River water because other states are not yet utilizing their full allotment. This situation will change in the near future and in 15 years California may not be able to use more than its apportionment of 4.4 million acre-feet.
In a "normal year," the average statewide runoff is about 71 million acre-feet. About 35 percent of this water is used by agricultural and urban users, 30 percent for environmental uses and 35 percent is lost to the Pacific Ocean to prevent saltwater intrusion into the fresh waterways of California.
During drought years, urban and agricultural water users face drastic rationing measures to conserve water. Drought emergency measures may reduce the available water to agricultural and urban water users and increase the amount of water diverted to protect fish and wildlife. Groundwater use can double from the average 8.5 to 9 million acre-feet in a normal year to more than 16 million acre-feet in a drought year. Extracting groundwater to make up for the difference between supply and demand results in overdrafting of groundwater. Overdrafting groundwater may result in water quality degradation, seawater intrusion and land subsidence.
There are many challenges and uncertainties related to water quantity in California. Most likely the amount of water needed to meet the expected population growth and maintain agricultural productivity will continue to increase. Except for desalination of seawater, new sources for water are limited and the most likely measures to meet the demand are conservation and recycling measures at the urban and agricultural levels.
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