California has a wide range of climates due, in part, to its mountain ranges, which influence weather patterns and cause more precipitation on the western sides of the ranges than on the eastern sides. Average statewide precipitation is about 23 inches and most of it, about 60 percent, is used by native vegetation or lost by evaporation. Estimated average annual runoff amounts to about 71 million acre-feet. Not all of this runoff can be developed for urban or agricultural use. Much of it maintains healthy ecosystems in California's rivers and estuarine systems. Available surface water supply totals 78 maf when out-of-state supplies from the Colorado and Klamath rivers are added.
Uneven distribution of water resources is part of the State's geography. Roughly 75 percent of the natural runoff occurs north of Sacramento; about 75 percent of the net water demand is south of Sacramento. Almost 29 maf, or 40 percent of California's surface water supply, originates in the North Coast Region. The largest urban water use is in the South Coast Region where roughly half of California's population resides, and the largest agricultural water use is in the San Joaquin River and Tulare Lake regions where fertile soils, a long, dry growing season, and water availability have combined to make this area one of the most agriculturally productive areas in the world. For example, Fresno County is the most productive county in the United States in terms of agricultural output measured in dollars. The largest environmental water use is in the North Coast Region where average annual dedicated natural flow in wild and scenic rivers amounts to 18 maf. Figure 3-1 shows the disposition of average annual water supplies.
Average runoff amounts are of some interest, but most of California's water development has been dictated by the extremes of droughts and floods. For example, the average yearly statewide runoff of 71 million acre-feet includes the all-time annual low of 15 maf in 1977 and the all-time high, exceeding 135 maf, in 1983. Figure 3-2 shows the distribution of average annual precipitation and runoff.) Stable and reliable supplies are required to sustain agricultural and urban economies, whereas environmental water needs vary with the natural hydrologic cycle.
The records of precipitation and runoff show that extremely dry periods frequently last several years. The seven-year drought of 1928-34 established the criteria commonly used to plan storage capacity or water yield of large Northern California reservoirs. From 1928 through 1937, the runoff was below average for ten straight years. Many reservoirs built since that time were sized to maintain a certain level of planned deliveries, or reliability, should there be a repeat of the 1928-34 dry period. The last 20 years have seen new record dry periods for one year (1977), two years (1976 through 1977), three years (1990 through 1992), and six years (1987 through 1992).
The Sacramento River Index is used both as a yardstick of Northern California water supply and in determining Delta water quality and flow criteria to be met by the federal Central Valley Project and the State Water Project. It classifies the runoff during a water year into five categories, ranging from critical (the driest) up to wet. Figure 3-3 shows the record of runoff for the index since 1906. The index is based on Water Right Decision 1485 and is the sum of unimpaired runoff in the Sacramento River (above Bend Bridge near Red Bluff), Feather River inflow to Oroville, Yuba River at Smartville, and American River inflow to Folsom. (Unimpaired runoff is the natural production of a stream unaltered by water diversions, storage, exports, or imports.) The major dry periods of this century include the 1929-34 dry period, the severe two-year drought of 1976-77, and the recent drought, in which five of the six years were classified as critical. The average of 18.4 maf shown on the chart is the currently used 50-year average; the average runoff for the entire 1906-93 period is slightly lower, about 17.8 maf.
The recent six-year drought is comparable to the 1929-34 sequence of dry years. Statewide precipitation from 1987-1992 was about 75 percent of average and annual streamflow was only about half of average. This drought was not quite the worst on record for the Sacramento Basin. Runoff in 1987-1992 was about 54 percent of average, about 1 percent more than the average during 1929-1934. Across the central part of the State, however, the recent drought was more severe than 1929-1934. The drought periods for Sacramento River Index runoff and for the San Joaquin River Index runoff (the sum of the unimpaired runoff in the San Joaquin River at Friant, and the Stanislaus, Tuolumne, and Merced Rivers) are shown in Figures 3-4 and 3-5. The extended 1929-34 drought was softened somewhat in the southern Sierra Nevada by an above-average water year in 1932. The recent drought, although varying somewhat from year to year, was an unrelieved string of six critical years in the southern Sierra Nevada.
In fall 1992, the storage in California's major reservoirs was somewhat under 12 maf, compared to a November 1 average of 21.4 maf. This was the lowest end-of-water-year storage level of the recent drought but was more than in 1977, when November 1 storage was only 7.6 maf.
Each drought is different. In 1986, a tree-ring study reconstructed 420 years of Sacramento River runoff. The study was conducted for DWR by the Laboratory of Tree-Ring Research of the University of Arizona. The reconstruction suggests that the 1928-34 drought was the worst since 1560. (Water year 1928 was near normal, but its dry spring led into a series of six dry or critical water years.) Table 3-1 was excerpted from the reconstruction. It shows other dry periods with consecutive years of runoff less than 15.7 maf (the historical median) lasting at least three years, prior to 1900, for the reconstructed Sacramento River Index. Also shown are the measured droughts since 1900.
The record reconstructed from the tree-ring study does not always match the record of measured runoff, so the weight to be given to the above information is unclear. However, the tree-ring widths provide us one way of comparing runoff records with estimates from a much larger span of history.
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The founding of the San Diego Mission in 1769 brought with it the start of water supply development in California. Water was diverted from the San Diego River to irrigate fields surrounding the mission. Similar developments accompanied other missions during ensuing years. After 1850, irrigation expanded significantly as the amount of irrigated agricultural land increased dramatically. This increase was abetted by the mining boom, which provided a nearby market for agricultural products. Since natural stream flows dropped during the summer, it was not long before small reservoirs were built to supplement low stream flows. A number of fairly large dams were built in Southern California by 1900, including Bear Valley, Hemet, Sweetwater, and Cuyamaca. Dams in Northern California were smaller and usually at the outlets of natural lakes or meadows. Total storage capacity on the Yuba River, one of the basins with a large amount of early development, exceeded 30,000 acre-feet by 1900.
During the 1920s, larger reservoirs were built in Northern California; in many cases, they were partially funded by hydroelectric power companies. Beginning in 1930, a number of critically dry years reduced snowmelt and streamflow and motivated another era of water storage development to provide more stable and reliable supplies.
There are now more than 1,200 nonfederal dams under State supervision (generally dams 25 feet or higher or those holding 50 af or more). The reservoirs formed by these dams provide a gross reservoir capacity of roughly 20 maf. There are also 181 federal reservoirs in California, with a combined capacity of nearly 22 maf. Taken together these 1,400 or so reservoirs can hold about 42 maf of water, which is a relatively small amount of storage in proportion to the 71 maf of annual runoff. The Colorado River alone, with a long-term average annual runoff of about 15 maf, has about 65 maf of storage. Table 3-5, at the end of this chapter, lists reservoirs storing 100,000 af or more in chronological order of construction. Figure 3-7 shows storage in 155 major reservoirs in California. Figure 3-8 shows historical development of reservoir capacity.
This chapter identifies developed surface water supplies by source. (Ground water, another important source of supply, is covered in Chapter 4.) The major categories are:
Local water projects were constructed and are operated by a wide variety of water and irrigation districts, agencies, municipalities, companies, and even individuals. Initially, local projects consisted of direct stream diversions. When these proved inadequate during the dry season, storage dams were built. As nearby sources were fully developed, urban areas began to reach out to more distant sources. Local agencies are finding it increasingly difficult to continue to undertake new water projects to meet their needs because potential sites for additional water projects are either environmentally sensitive, too costly to develop, or both. Rural areas, in particular, have limited means of repaying loans for water projects. Opportunities for local conjunctive use programs are limited because mountain and foothill ground water basins tend to be limited. On average, local surface water supply projects meet about one-third of California's water needs.
The majority of local water supplies are in-area (within one region) diversion and storage systems. Most local surface projects are relatively small, but some are large-volume projects. Some examples of these projects are the Exchequer and Don Pedro (both old and new) dams on the Merced and Tuolumne rivers. Another example is Bullards Bar Dam on the Yuba River, built by Yuba County Water Agency. Some irrigation districts have taken advantage of upstream projects built primarily for hydroelectric power production. These facilities also incidentally regulate stream flows, create more usable water supplies during the dry summer months, and provide flood control and recreational benefits.
Figure 3-9 shows regional water transfers at the 1990 level of development. Most of these transfers are through the Delta, the hub of California's surface water delivery system. Until solutions to complex Delta problems are identified and put into place, 1990 level water transfers cannot be sustained in the future.
The first long-distance, inter-regional water transfer project in California was the Los Angeles Aqueduct, completed by the City of Los Angeles in 1913. The aqueduct stretches over 290 miles from the Owens Valley and had an original capacity of 330,000 af per year. A second section was added in 1970, which increased its potential annual deliveries to 480,000 af per year. However, these projects were developed without minimum flows for fisheries in creeks tributary to Mono Lake and without consideration of lake levels. Environmental problems resulting from diversions have resulted in recent restrictions on the use of water tributary to Mono Lake and on ground water pumping in the Owens Valley (see Chapter 2). These restrictions have reduced the dependable supply of the Los Angeles Aqueduct to about 200,000 af in drought years.
In the 1920s, the East Bay cities of the San Francisco Bay Region turned to Sierra Nevada watersheds for additional water. The East Bay Municipal Utility District completed the Mokelumne Aqueduct from Pardee Reservoir in 1929. With the addition of a third barrel in 1965, this aqueduct's capacity was increased from 224,000 af per year to 364,000 af per year. Camanche Reservoir was added in 1963. Again, drought year supplies in the Pardee-Camanche Reservoir system are not always adequate to sustain full aqueduct capacity diversions.
In 1934, the City of San Francisco completed the Hetch Hetchy Aqueduct system, which diverts water from the Tuolumne River to serve San Francisco, San Mateo, northern Santa Clara, and portions of southern Alameda counties. (Hetch Hetchy Dam began operating in 1923.) The current conveyance capacity of the Hetch Hetchy Aqueduct is about 330,000 af per year. Its primary supply reservoirs are Hetch Hetchy, Lake Lloyd (Cherry Valley), and Lake Eleanor. The City of San Francisco also has exchange water storage in Don Pedro Reservoir which allows water that would otherwise go to Turlock and Modesto irrigation districts to be diverted through the Hetch Hetchy Aqueduct.
The All-American Canal System was authorized under the Boulder Canyon Project Act of December 21, 1928. It diverts Colorado River water to the Imperial and Coachella valleys. Construction began in 1934, following construction of Hoover Dam on the Colorado River. The first deliveries of irrigation water to Imperial Valley were in 1940. The Coachella Canal and distribution system was completed in 1954. The Imperial Irrigation District assumed responsibility for operation and maintenance of the All-American Canal in 1952. The Coachella Valley Water District is responsible for the operation and maintenance of the Coachella Canal portion of the system. The system has the capacity to divert over 3 maf annually from the Colorado River for use in the Imperial and Coachella valleys.
The fifth major inter-regional conveyance project in California built by a local agency is the Colorado River Aqueduct, which diverts Colorado River water from Lake Havasu above Parker Dam to the South Coast Region. Constructed in the 1930s by the Metropolitan Water District of Southern California, this aqueduct began operation in 1941. The Colorado River Aqueduct was sized for about 1.2 maf per year but has carried as much as 1.3 maf during some of the recent drought years. (See the Colorado River section in this chapter.)
The preceding local import systems are not the only ones in California, but they account for over 95 percent of the local project water transferred among hydrologic regions.
Planning for the multipurpose State Water Project began soon after World War II when it became evident that local and federal water development could not keep pace with the state's rapidly growing population. Voters authorized construction of the project in 1960 by ratifying the Burns-Porter Act. At that time, the plans recognized that there would be a gradual increase in water demand and that some of the supply facilities could be deferred until later. The SWP's major components include the multipurpose Oroville Dam and Reservoir on the Feather River, the Edmund G. Brown California Aqueduct, South Bay Aqueduct, North Bay Aqueduct, and a portion of San Luis Reservoir. Delta water transfer facilities were part of the original plan, and additional Sacramento and North Coast basin supply reservoirs were envisioned. Contracts were signed for an eventual delivery of 4.23 maf. Service areas of the present 29 contracting agencies are shown in Figure 3-10. Figure 3-12 depicts a history of SWP water deliveries from 1962 to 1993. Generally, San Joaquin Valley use of SWP supply has been near full contract amounts since about 1980 (except during very wet years and during deficient-supply years), whereas Southern California use has only built up to about 60 percent of full entitlement.
The initial features of the SWP begin with three small reservoirs in the upper Feather River basin in Plumas County: Lake Davis, and Frenchman and Antelope Lakes. Farther downstream in the foothills of the Sierra Nevada is the 3.5-maf Lake Oroville, the second largest reservoir in California, where winter and spring flows of the Feather River are stored (see Figure 3-11). The 444-mile California Aqueduct is the state's largest and longest water conveyance system, beginning in the southwest Delta at Banks Pumping Plant and extending to Lake Perris south of Riverside, in Southern California. Delta water is pumped southward and westward, with amounts exceeding immediate needs temporarily stored in the 2.0-maf San Luis Reservoir (which is shared with the CVP). Of the contracted amounts, about 2.5 maf of water is destined for south of the Tehachapis, nearly 1.36 maf to the San Joaquin Valley, and the remaining 0.37 maf to the San Francisco Bay and Central Coast regions and the Feather River area. At the southern end of the San Joaquin Valley, pumps at the Edmonston Pumping Plant lift water 1,926 feet, sending flows through the Tehachapi Mountains by tunnels and into Southern California. Slightly over 1.5 maf was pumped at Edmonston Pumping Plant in 1990.
The estimated seven-year average dry-period yield of the SWP with its current facilities operating according to Water Right Decision 1485 requirements is about 2.4 maf per year. Entitlement demand of SWP contractors for the year 2010 is an estimated 4.1 maf. To augment project supply, additions to the SWP are proposed and include: Delta facilities; interim south Delta facilities; the Kern Water Bank; Los Banos Grandes; and possible conjunctive use of surface storage and ground water in the Sacramento and San Joaquin valleys; and short- and long-term water purchases. These projects and programs are discussed in Chapter 11.
In the short term, SWP contractors relying on the Delta for all or a portion of their supplies face great uncertainty in terms of water supply reliability due to the uncertain outcome of a number of actions currently being undertaken to protect aquatic species in the Delta. Until solutions to complex Delta problems are identified and put into place, many will experience more frequent and severe water supply shortages.
The U.S. Bureau of Reclamation's Central Valley Project is the largest water storage and delivery system in California, covering 29 of the State's 58 counties. The project's features include 18 federal reservoirs, plus 4 additional reservoirs jointly owned with the State Water Project (primarily the San Luis Reservoir). The keystone of the CVP is the 4.6-maf Lake Shasta, the largest reservoir in California. The reservoirs in this system provide a total storage capacity of slightly over 12 maf, nearly 30 percent of the total surface storage in California, and deliver about 7.3 maf annually to agricultural, urban, and wildlife uses.
The federal government began construction of the CVP in the 1930s, as authorized under the Rivers and Harbors Act of 1937. CVP purposes expanded to include river regulation, flood control, and navigation; later reauthorization included recreation and fish and wildlife purposes. Initial authorization covered facilities such as Shasta and Friant Dams, Tracy Pumping Plant, and the Contra Costa, Delta-Mendota, and Friant-Kern Canals. Later authorizations continued to add additional facilities such as Folsom Dam (authorized in 1949), San Luis Unit (authorized in 1960), and New Melones Dam (authorized in 1962).
A large 2.3-maf multipurpose dam, primarily for flood control and water supply on the American River, Auburn Dam, was authorized by Congress in 1965 as an addition to the Central Valley Project. Foundation and other preparatory work for construction were halted by concerns for safety caused by the 1975 Oroville earthquake. After study, the dam's design was changed in 1980 from a concrete arch to a gravity structure. Cost estimates have exceeded the original authorization, so new authorization is needed before work can resume. The proposed dam is now a source of controversy between proponents and those who wish to preserve the American River canyon as is. As currently planned, Auburn Reservoir could have provided somewhat over 0.3 maf per year of new water yield to the CVP.
The flood of 1986 revealed that flood protection in the metropolitan Sacramento area is inadequate. In 1992, a proposal by the Corps of Engineers to build a 500,000- acre-foot "dry dam" for flood control only at the Auburn site did not pass Congress because of opposition from environmentalists and from supporters of a multipurpose dam. The Corps of Engineers and USBR, in cooperation with local agencies and the State, are continuing studies to develop a management plan for the American River to provide for the area's flood control and water supply needs.
The CVP supplies water to over 250 long-term water contractors in the service areas shown in Figure 3-13, whose contracts total 9.3 maf including 1.4 maf of Friant Division Class 2 supply available in wet years. Of the 9.3 maf, 6.2 maf is project water and 3.1 maf is water right settlement water. Average-year deliveries in the past decade have been around 7 maf. Water right settlement water is water covered in agreements with water rights holders whose diversions were in existence before the project was constructed. Since construction of project reservoirs altered the rivers' natural flow upon which these diverters had relied, contracts were negotiated to serve the users stored water to supplement river flows available under their rights. CVP water right settlement contractors (called prior right holders) on the upper Sacramento River receive their supply from natural flow and storage regulated at Shasta Dam; settlement contractors on the San Joaquin River (called exchange contractors) receive Delta water via the Delta-Mendota Canal as explained below.
About 90 percent of the CVP water has gone to agricultural uses in the recent past; this includes water delivered to prior right holders. CVP water is used to irrigate some 19,000 farms covering 3 million acres. Currently, increasing quantities of water are being served to municipal customers. Urban areas receiving CVP water supply include Redding, Sacramento, Folsom, Tracy, most of Santa Clara County, northeastern Contra Costa County, and Fresno. Recent firming up of environmental supplies under the provisions of the CVP Improvement Act of 1992 are described in Chapter 2.
Water stored in CVP northern reservoirs is gradually released down the Sacramento River into the Sacramento-San Joaquin Delta, where it helps meet demand along the river and quality and flow requirements in the Delta. The remainder is exported via the Contra Costa Canal and the Delta-Mendota Canal. Excess water during the winter is conveyed to off-stream San Luis Reservoir on the west side of the valley for subsequent delivery to the San Luis and San Felipe units. A portion of the Delta-Mendota exports are placed back into the San Joaquin River at Mendota Pool to serve, by exchange, water users who have long-standing historical rights to use of San Joaquin River flow. This exchange enabled the CVP to build Friant Dam, northeast of Fresno, and divert a major portion of the flow there farther south in the Friant-Kern Canal (and some water northward in the Madera Canal). The Corning and Tehama-Colusa Canals serve an area on the west side of the Sacramento Valley. Other water supplies are furnished to districts and water rights holders in the Sacramento Valley. American River water stored in Folsom Reservoir is used mainly for stream flow and Delta requirements, including CVP exports. More recently, the San Felipe Unit was added to serve coastal counties west of San Luis Reservoir. New Melones Reservoir will be serving an area on the eastern side of the San Joaquin Valley as well as providing downstream water quality and fishery flows. Operations in the Delta are coordinated with the SWP to meet water quality and other standards set by the State Water Resources Control Board, and more recently by federal fisheries agencies.
Figure 3-14 shows historical CVP water deliveries since 1960. The drop in 1977 and 1990-92 deliveries was caused by shortages in supply during the critically dry years. CVP water deliveries to agricultural and urban users have been reduced by the passage of the CVP Improvement Act of 1992. As a result, CVP contractors will undergo more frequent and severe shortages. (A more comprehensive discussion about the CVP Improvement Act is in Chapter 2.) Figure 3-15 shows a history of CVP hydroelectric energy production since 1960. Note the substantial drop in hydroelectric production during the 1987-92 drought.
In the short-term, CVP contractors relying on the Delta for all or a portion of their supplies face great uncertainty in terms of water supply reliability due to the uncertain outcome of a number of actions currently being undertaken to protect aquatic species in the Delta. Until solutions to complex Delta problems are identified and put into place, many will experience more frequent and severe water supply shortages. For example, in 1993, an above-normal runoff year, environmental restrictions limited CVP deliveries to Westlands Irrigation District to only 50 percent of contracted supply. Further, the CVPIA reallocates 800,000 af of CVP supplies for fisheries in Central Valley streams; 200,000 af for wildlife refuges in the Central Valley; and about 120,000 af of increased flow for the Trinity River.
Other federal water projects include those constructed by the U.S. Army Corps of Engineers or the U.S. Bureau of Reclamation. Some of the larger projects in this category are: the Klamath Project on the California-Oregon border; the Orland Project on Stony Creek (west side of the Sacramento Valley); the Solano Project on Putah Creek,which stores water in Lake Berryessa in Napa County and conveys water through Putah South Canal in Solano County; New Hogan Reservoir in Calaveras County; the four major dams and reservoirs on the east side of the Tulare Lake Region-Pine Flat, Terminus, Success, and Isabella; and Cachuma and Casitas reservoirs in Santa Barbara and Ventura counties. Altogether these projects deliver about 1.2 maf annually.
In a 1964 U.S. Supreme Court decree, annual use of 7.5 maf of Colorado River water was apportioned among the three lower division states of Arizona, Nevada, and California. Arizona could begin using its apportionment of 2.8 maf now that the Central Arizona Project is operating, but current repayment issues associated with sales of water to agricultural users are delaying the buildup in demand. Arizona's Colorado River water use in 1993 was 2.2 maf. Nevada's water use is expected to reach its 0.3-maf apportionment in a little over a decade. Nevada used 0.18 maf in 1993. California's use in 1993 was about 4.8 maf.
California's basic apportionment of Colorado River supplies is 4.4 maf per year, plus half of any excess or surplus water. Because of wet winters in the early to mid-1980s, and because Arizona and Nevada were not yet using their full apportionment, California has been able to use from 4.5 to 5.2 maf annually between 1986 and 1992. Since 1980, the highest and the lowest sequence of unregulated Colorado River runoff has occurred, with the peak year in 1984 and the driest in 1990. Between 1988 and 1992, Colorado River runoff was far below average, and by 1991 storage on the main river system fell to less than average. Runoff in 1993 was above average and, by July 1, storage in Lakes Mead and Powell had increased about 6 maf over the previous year's storage. California's use of Colorado River water can be limited in the future to 4.4 maf in any year by the Secretary of the Interior.
The agricultural water diverters in the Colorado River Region are Palo Verde Irrigation District, Imperial Irrigation District, the Reservation Division of the Yuma Project, and Coachella Valley Water District (see Figure 3-16). These water users have priority rights to the first 3.85 maf of California's Colorado River supply. This would leave 550,000 af, less the water used by Native Americans, for MWDSC's Colorado River Aqueduct, instead of the 1.2 maf that it has been using in recent years. Further reductions in Metropolitan's supply are also expected; 55,000 af may be used by Native American Tribes and others along the Colorado River. To partially offset potential reductions, MWDSC has executed a number of agreements to increase its water supplies. In December 1988, Imperial Irrigation District and MWDSC reached an agreement that provides funding for conservation projects in the Imperial Valley after the State Water Resources Control Board issued order WR 88-20 requiring IID to conserve 100,000 af per year within a certain period of time. When completed, these projects will save an estimated 106,000 af of water annually. MWDSC is funding the construction, operation, and maintenance of the projects; the estimated total cost is $222 million (1988 dollars). In exchange, MWDSC will be able to divert additional water, under certain conditions, from the Colorado River through its Colorado River Aqueduct. The amount of additional Colorado River water MWDSC diverts is to be equivalent to the amount of water conserved through the MWDSC-financed projects in the event MWDSC's available allocation is reduced to an amount below its aqueduct capacity. As the result of a contract between the Coachella Valley Water District and the United States, the first 49 miles of the Coachella Canal were lined to save 132,000 af annually, which can also be made available to MWDSC under certain conditions.
Water conservation measures implemented by IID since 1954 have decreased the amount of water entering the Salton Sea. With less relatively fresh water entering the Salton Sea, its salinity concentrations have increased somewhat more rapidly than would have happened otherwise and have affected the artificial fishery planted by DFG. The State Water Resources Control Board considered this matter in issuing order WR 88-20. Implementation of the water conservation measures has also reduced the potential for flooding from higher Salton Sea stages.
Water recycling, formerly known as waste water reclamation, has been intentionally used as a source of nonpotable water in California for nearly a century. In recent years, more stringent treatment requirements for disposal of municipal and industrial waste water have reduced the incremental cost of obtaining the higher level of treatment required for use of recycled water. This higher level is needed so that recycled water can be safely used for a wider variety of applications. Part of the recycled water used will lessen demand for new fresh water supplies.
Technology available today allows municipal waste water treatment systems in some regions to consistently produce safe water supplies at competitive costs. The degree of treatment depends on the intended use, and public health protection is the paramount criterion for judging the level of treatment needed. As a minimum, waste water is treated to a secondary level to remove dissolved organic materials. Secondary effluent can be treated to a tertiary level by additional filtering and disinfecting, but the cost can be high in comparison to other fresh water supply augmentation options. Sometimes reverse osmosis desalination may be required to reduce the salt content; in such cases, it is possible for the recycled water to be of higher quality than the original source. However, the added costs of desalination can make water recycling infeasible in many regions.
A July 1993 report by the WateReuse Association of California summarized present and future potential water recycling data gathered during a 1992 survey. About 240 agencies were contacted, and 111 responded to the survey. Its purpose was to determine the agencies' plans, projections, and vision for future water reuse. One of the purposes of the survey report was to encourage agencies to set realistic goals, and develop long-term strategies to better meet future water needs. It was noted that water reuse had increased from about 270,000 af per year in 1987 to over 380,000 af per year by 1993. Water reuse as reported in the 1993 survey is shown in Figure 3-17 and Table 3-3. Future estimates for water recycling are discussed in Chapter 11.
Most of the 384,000 af recycled is in the South Coast, Central Coast, and Tulare Lake regions. Some uses of recycled water, such as environmental enhancement or landscape projects, are new uses that would not have received fresh water in the absence of a water recycling project because imported fresh water was too costly or not available. In addition, outflow from waste water treatment plants in the Central Valley is generally put into streams or ground water basins and reused. Recycling of such outflow, therefore, does not generate new water supply.
Some constraints to fully implementing all potential water recycling options include:
Table 3-4 specifies a number of possible nonpotable uses of recycled water and the degree of treatment necessary for the type of use, as assessed by the California Department of Health Services in 1992. The "Disinfected Secondary-2.2" column indicates the higher standard of 2.2 coliform bacteria per 100 milliliters, and the "Disinfected Secondary-23" column indicates the less-treated reclaimed water containing 23 coliform bacteria per 100 milliliters.
The potential for increased use of recycled water in the future depends on many factors and is discussed in Chapter 11. The primary source of raw supply would be the estimated 2.5 to 3 maf of treated wastewater discharged annually into the ocean from California's coastal cities. Smaller amounts of reclaimed water could come from reclaiming brackish ground water, including contaminated ground water or ground water with high nitrate content, and from desalination of ocean water.
Several unconventional methods have been used to augment surface water supply in certain areas of California: use of gray water, long-range weather forecasting, watershed management, weather modification, and sea water desalination.
For the residential homeowner, some waste water can be directly reused as gray water (used household water). Gray water can be used in subsurface systems to irrigate lawns, fruit trees, ornamental trees and shrubs, flowers, and other ornamental ground cover. Water from the bathroom sink, washing machine, bathtub, or shower is generally safe to reuse, whereas water from a toilet, kitchen sink, or dishwasher or water used in washing diapers should not be directly reused. Care must be taken so that children and others do not come in direct contact with gray water, and any food from areas irrigated by subsurface systems that use gray water should be rinsed and cooked before being consumed.
Gray water has been used by some homeowners in certain coastal urban areas during extreme drought to save their landscaping. In the past, health concerns and lack of information limited use of gray water. In 1992, recognizing that gray water could be used safely with proper precautions, the California Legislature amended the Water Code to allow gray water systems in residential buildings subject to appropriate standards and with the approval of local jurisdictions. Statewide, residential use of gray water will be legal by fall 1994.
Accurate advance weather information-extending weeks, months, and even seasons ahead-would be invaluable in planning water operations in all types of years-wet, dry, and normal. Had it been known, for instance, that 1976 and 1977 were to be extremely dry years or that the drought would end in 1977, water operations would have been planned somewhat differently and the impacts of the drought could have been lessened. The response to the 1987-92 drought might have been slightly improved by storing more water in the winter of 1986-87, pursuant to a forecast, and using more of the remaining reserves in 1992, the last year of the drought.
The potential benefits of dependable long-range weather forecasts could probably be calculated in hundreds of millions of dollars, possibly even in billions, and the value would be national. For this and other reasons, research programs to investigate and develop such forecasting capability would most appropriately be conducted at the national level. The National Weather Service routinely issues 30- and 90-day forecasts, and the Scripps Institution of Oceanography in San Diego, California (until recently), and Creighton University in Omaha, Nebraska, are engaged in making experimental forecasts. However, their predictions are not sufficiently reliable for project operation. These may be improved by current research on global weather patterns including the El Nino-Southern Oscillation in the eastern Pacific Ocean.
Weather modification, commonly known as cloud seeding, has been widely practiced in California for many years. Most projects have been along the western slopes of the Sierra Nevada and some of the coast ranges. Before the recent drought, there were about 10 to 12 weather modification projects operating, with activity typically increasing during dry years. By spring 1991, the number of programs operating in California had increased to 20. New projects started during the drought include programs involving the Lake Berryessa area; San Gabriel Mountains; Calaveras, Tuolumne, Monterey, San Luis Obispo, San Diego, and eastern Santa Clara counties; and the SWP experimental propane project in the upper Feather River basin. A couple of programs were dropped in the 1992-93 season, when 18 programs were ready to operate. (Many areas suspended operations later as the winter turned wet.)
Operators engaged in cloud seeding have found it beneficial to seed rain bands along the coast and in orographic clouds over the mountains. The projects are operated to increase water supply or hydroelectric power. Although precise evaluations of the amount of water produced are difficult and expensive to determine, estimates range from a 2- to 15-percent increase in annual precipitation, depending on the number and type of storms seeded.
The Department of Water Resources, on behalf of the SWP, began a planned five-year demonstration program of cloud-seeding in the upper middle fork Feather River basin during the 1991-92 season. The project was testing the use of pure liquid propane injected into the clouds from generators on a mountain-top. The liquid propane is essentially a chilling agent that helps produce ice crystal nuclei and enhance snowfall. The program was terminated after three years, in 1994, due to several overriding considerations.
A 1993 U.S. Bureau of Reclamation feasibility study for a cloud seeding program in the watersheds above Shasta and Trinity Dams indicated good potential for the Trinity River Basin, but the study cast doubt about the effectiveness of a project for Shasta Lake. The Bureau has done substantial cloud seeding research in the Colorado River Basin. In September 1993, it published Validation of Precipitation Management by Seeding Winter Orographic Clouds in the Colorado River Basin. However, the Bureau is phasing out its participation in weather modification projects.
Interest in using cloud seeding to provide both short-term and long-term drought relief remains high. The technique is more successful in near-normal years, when more moisture in the form of storm clouds is present to be treated. It is also more effective when combined with carryover storage to take full advantage of additional precipitation and runoff.
Watershed management can increase stream flow by controlling the growth of vegetation, usually by reducing the density of brush and tree cover and increasing the portion in grasses. In other cases, vegetation management that encourages growth of certain species can protect watersheds by reducing soil erosion, thereby reducing sedimentation in reservoirs and canals. Water supply gained by such means, although a small fraction of total runoff, can cost less than supplies developed by more conventional means. However, extensive expanses of land must be managed to significantly increase statewide supplies. The primary purposes of vegetation management today are to improve range, reduce wildfires, and enhance wildlife habitat.
National forest lands provide about half of the stream flow runoff in the state. National forest management plans show that if the present management plans had been in place prior to 1982, the average runoff from national forests would have been increased by about 290,000 acre-feet (an increase of nearly 1 percent). Much of this water flows uncontrolled to the sea, either because of location (for example, the North Coast Region) or because there is no space available in reservoirs to hold the water. However, about 100,000 af could either be stored in surface reservoirs or ponded and allowed to percolate into ground water aquifers. There may be a potential to boost these amounts of runoff and water yield by roughly another 25 percent by implementing recommended or selected forest management plans.
Sea water desalination can be a cost-effective water supply alternative for some coastal communities that have limited local supplies and are relatively far from the statewide distribution system, or communities that are concerned about water service reliability. Desalination plants in Avalon (on Catalina Island) and the City of Santa Barbara are examples of such projects. However, a major limitation for sea water desalting is its high cost, much of which is directly related to its high energy requirements. Sea water desalting plants could be designed to operate only during droughts to augment other supplies and avoid the relatively high costs during wet periods. They could also be downsized and operated continuously in conjunction with ground water, reducing ground water pumping during wet periods and providing more ground water supplies for drought periods. Chapter 11 presents a broader discussion of the potential for future desalination in California.
Bulletin 1, Water Resources of California, was published in 1951. DWR
should initiate work to update and maintain this resource document to incorporate
more recent hydrologic data, including 40 more years of runoff data.
Back to Bulletin 160, Volume I Index