The Colorado River Region encompasses the southeastern corner of California. The region's northern boundary, a drainage divide, begins along the southern edge of the Mojave River watershed in the Victor Valley area of San Bernardino County and extends northeast across the Mojave Desert to the Nevada state line. The southern boundary is the Mexican border. A drainage divide forms the jagged western boundary through the San Bernardino, San Jacinto, and Santa Rosa mountains and the Peninsular ranges (which include the Laguna Mountains). The Nevada state line and the Colorado River (the boundary with Arizona) delineate the region's eastern boundary.
Covering over 12 percent of the total land area in the State, the region is California's most arid. It includes volcanic mountain ranges and hills; distinctive sand dunes; broad areas of the Joshua tree, alkali scrub, and cholla communities; and elevated river terraces. Despite its dry climate and rugged terrain, the region contains some of the State's most productive agricultural areas and vacation resorts. (See Appendix C for maps of the planning subareas and land ownership in the region.)
Much of the region's topography consists of flat plains punctuated by numerous hills and mountain ranges. Faulting and volcanic activities are partially responsible for the presence of many abrupt mountain ranges. The San Andreas fault slices through portions of the Coachella and Imperial valleys.
A prominent topographic feature is the Salton Trough in the south-central part of the region. Oriented in a northwest-southeast direction, the trough extends from San Gorgonio Pass in the north to the Mexican border and beyond to the Gulf of California. It includes the Coachella Valley in the north and Imperial Valley in the south. The low point of the trough is the Salton Sea, which was created between 1905 and 1907 when the headworks of an irrigation canal conveying Colorado River water to Imperial Valley broke. Large volumes of water flowed into the Salton Sink, resulting in the sea that exists today. In September 1993, the Salton Sea's water surface level was about 227 feet below sea level.
The climate for most of the region is subtropical desert. Average annual precipitation is much higher in the western mountains than in the desert areas. Winter snows generally fall above 5,000 feet; snow depths can reach several feet at the highest levels during winter. Most of the precipitation in the region falls during the winter; however, summer thunderstorms can produce rain and local flooding in many areas.
Drainage in the region is internal except for the eastern portion, which drains into the Colorado River. Portions of the Coachella Valley are drained by the Whitewater River, which terminates in the Salton Sea. The Imperial Valley is drained by the Alamo and New rivers, which originate in Mexico and terminate in the Salton Sea.
The Colorado River Region's population increased 48 percent from 313,000 in 1980 to 464,200 in 1990. Most of the population is concentrated in the Coachella and Imperial valleys. Major cities in the Coachella Valley include Palm Springs, Indio, Cathedral City, and Palm Desert. Other urban centers in the region include the Cities of El Centro, Brawley, Yucca Valley, and Calexico in Imperial Valley; the Cities of Beaumont and Banning in the San Gorgonio Pass area; and the cities of Needles and Blythe along the Colorado River. Table CR-1 shows the population projections for this region.
Less than 2 percent of California's population resides in the region. Urban development in the Coachella Valley is proceeding at a rapid pace due to affordable housing and the area's aesthetic appeal. Much of the growth is attributed to retirees and others who find the climate and real estate settings attractive.
Federal and state government-owned lands account for about 14,270 square miles, or 72 percent, of the total land area of the region. There are several military training and testing grounds, including the large U.S. Marine Corps Military Training Center at Twenty-Nine Palms and the gunnery range in the Chocolate Mountains. Major parks include Joshua Tree National Monument and Anza-Borrego Desert State Park. The U.S. Bureau of Land Management oversees use of much of the desert lands.
The number one industry and most important source of income for the region is agriculture. Almost 90 percent (647,000 acres) of the developed private land is used for agriculture, most of which is in the Imperial Valley. Because of a lack of significant rainfall, all crops planted and harvested in these areas receive irrigation water, mostly from the Colorado River. Some ground water supplies are used as well. Some of the more prominent crops include alfalfa, winter vegetables, spring melons, table grapes, dates, Sudan grass, and wheat. Figure CR-1 shows land use, along with imports and exports, for the Colorado River Region.
Most of the remaining industries are generally associated with the region's intensive agricultural activities. These industries process, pack, and distribute harvested crops, or manufacture and sell agricultural equipment and materials. Other industries in the region include geothermal and alternative energy developments near the Salton Sea and in Imperial Valley, wind farms near San Gorgonio Pass, and gold and miscellaneous mining operations.
The major issue involving land use in the Colorado River Region is how to balance long-term preservation and protection of the land while providing various kinds of recreational opportunities. Recent discussions have centered on proposed federal legislation that would enlarge and give national park status to the East Mojave National Scenic Area and Joshua Tree National Monument.
At first, the region depended mostly on developed ground water supplies supplemented with a minimum of surface water. Water demands now are met primarily from surface deliveries from the following sources: the Colorado River (through the All-American and Coachella canals, local diversions, and the Colorado River Aqueduct through an exchange for State Water Project water), ground water, local surface water, and reclaimed water. Figure CR-2 shows the region's 1990 level sources of supply.
In 1938, the U.S. Bureau of Reclamation began conveying Colorado River water, via the All-American Canal, to the Imperial and Coachella valleys. The All-American Canal can carry 15,100 cubic feet per second, which has provided these areas with an adequate and reliable supply of water. There are no major water supply reservoirs in the region beyond those on the Colorado River. Table CR-2 shows water supplies with existing facilities and water management programs.
The Colorado River also supplies water to areas served by the Colorado River Aqueduct, owned by the Metropolitan Water District of Southern California. The California apportionment of Colorado River water is 4,400,000 af annually plus any unused Arizona and Nevada water and one-half of any surplus made available by the Secretary of the Interior. California consumptively used over 5,200,000 af of Colorado River water in 1990, of which 3,900,000 af was used in the Colorado River Region. Water from the Colorado River makes up about 95 percent of the region's total supply.
Four State Water Project contractors are located in the region: Desert Water Agency, Coachella Valley Water District, Mojave Water Agency and San Gorgonio Pass Water Agency. The SWP does not extend into the region at this time. (The Morongo Basin Pipeline will bring SWP water into the Colorado Region in 1994.) MWDSC has an exchange agreement with Desert Water Agency and Coachella Valley Water District that allows MWDSC to take the two agencies' SWP entitlement water. In return, MWDSC releases water from its Colorado River Aqueduct for ground water recharge in the Coachella Valley. Local surface water supply in the Coachella subarea amounted to about 6,000 af in 1990. This supply is derived from the Whitewater River; however, the supply is not dependable in times of drought.
About 7,000 af of fresh water was produced by water recycling in 1990. About 2,000 af of the water recycling occurred in the Coachella. Most of the recycled water was applied to golf courses and resort hotel common areas.
Total ground water supplies for 1990 were about 155,000 af, almost 4 percent of the region's total supply. The Coachella PSA accounted for about 85,000 af of the ground water use in the region, 52,000 af of which was overdraft. Streamflow percolation, subsurface inflow, periodic Colorado River flooding, and canal leakage all provide ground water basin recharge at various locations in the region.
Future water management programs are presented in two levels to better reflect the status of investigations required to implement them.
The following sections summarize water management programs under active consideration in the region.
Drought Water Management Strategies. State requirements for water shortage contingency plans for urban water providers encourage urban water agencies to implement water conservation measures and practices and to plan strategies for managing shortages. The Federal Reclamation Reform Act of 1982 and the CVPIA of 1992 require that water suppliers who contract with the U.S. Bureau of Reclamation prepare water conservation plans and update them every five years. Most of the larger agencies in the region would be affected. (Volume I, Chapter 2 of the California Water Plan Update presents more details of the 1982 and 1992 acts.) These planning steps constitute the major drought water management efforts in the region. The recent drought did not adversely affect the area due to ample carryover of supplies in lower Colorado River reservoirs.
Water Management Options with Additional Facilities. The Mojave Water Agency is constructing the Morongo Basin Pipeline which will convey State Water Project water from the Hesperia turnout of the California Aqueduct to the Morongo Basin-Johnson Valley area. The design capacity of the pipeline is 22 cubic feet per second. Construction is scheduled to be completed in 1994. The San Gorgonio Pass Water Agency has no physical facilities for transporting its SWP entitlement of 17,300 af. The agency is currently designing facilities to take delivery of its entitlement plus an additional 50,000 af to be used conjunctively in the ground water basin. Under this plan, facilities would have a carrying capacity of 32 cfs. The facilities are expected to be on-line in 1995 or 1996. An estimated 1,000,000 af of storage space is available within the San Gorgonio ground water basins. To date, two 1,000-foot-deep exploration wells and two monitoring wells (100 feet and 250 feet deep) have been established in the potential recharge area. San Gorgonio serves the cities of Banning and Beaumont and the Morongo Indian Reservation. Table CR-3 shows water supplies with additional Level I water management programs.
The 1990 level annual net water demand within the Colorado River Region is about 4,124,000 af. Agricultural irrigation accounts for 83 percent of the region's net water use, while municipal and industrial use accounts for almost 5 percent. The Colorado River Region's agricultural water use is the fourth highest in the State. Even though the region has a small permanent population base, the water requirements of its recreation and tourism industries make up a large portion of the region's municipal and industrial net water use of 204,000 af. Figure CR-3 shows 1990 level net water demands for the Colorado River Region.
Population projections indicate that urban applied water demand will increase about 106 percent between 1990 and 2020, due to an expected population increase of roughly 117 percent during the same period. Table CR-4 shows the total urban applied, net water demand, and depletion for the Colorado River Region through 2020. Much of the increase in urban water demand can be attributed to the development of recreational and resort facilities in Coachella Valley. Figure CR-4 shows the 1990 level urban applied water use by sector.
Average 1990 level urban net water use for the region was 579 gpcd. However, values range from 853 gpcd in the Coachella PSA to 163 gpcd in the less densely populated areas of the Twenty-Nine Palms PSA. Average per capita water use is expected to decrease by about 4 percent between 1990 and 2020, primarily due to increased conservation efforts.
The high per capita values in 1990 are attributable to a large tourism industry, greater landscape irrigation requirements, and a rise in the number of people who reside in the region part-time. Lower per capita values are common in areas where the residential landscaping requirements are lower and commercial and industrial water uses are small.
The 1990 level irrigated crop acreage for the Colorado River Region amounted to 749,000 acres. Table CR-5 shows irrigated crop acreage forecasts to 2020. Most of the major agricultural operations in the region are in the Imperial Valley, Colorado River, and Coachella PSAs. Minor reductions of about three percent in total irrigated crop acres are forecasted to occur between 1990 and 2020. However, increases will occur in the planted and harvested acres for certain high-market-value crops, such as fresh market vegetables. Demand by both international and domestic markets for fresh vegetables will probably encourage growers to maintain current levels of crop production and, if possible, plant and harvest additional acres. Other crops expected to show minor to moderate increases are grains, citrus and subtropical fruit, sugar beets, and cotton. For cotton, current boll worm problems could be rectified and additional acres planted, mainly in Imperial Valley. The silverleaf whitefly infestation, primarily in Imperial Valley, has caused temporary minor reductions in the recent planted and harvested acreage. Eradication and management efforts should mitigate the problems caused by these pests and allow crop acreage to return to normal levels. Table CR-6 shows the 1990 level evapotranspiration of applied water for the region.
The four major crops in terms of acreage and total applied water use are alfalfa, truck (vegetables and nursery), grains, and miscellaneous field. In 1990, alfalfa used roughly 50 percent of the total applied agricultural water. Figure CR-5 compares 1990 crop acreages, evapotranspiration, and applied water for major crops.
Reductions in irrigated acres are expected for crops or crop categories with low or fluctuating market values, such as alfalfa, corn, and miscellaneous field crops. Market competition (international and domestic) and the pressures from urban encroachment may cause decreases in acres planted with table grapes in the Coachella Valley. Total 1990 agricultural applied water demand was about 3,705,000 af and net water demand was about 3,439,000 af. Table CR-7 summarizes the 1990 and forecasted agricultural water demand in the region.
Minor reductions in crop acreage and applied water use are expected for the region. Forecasts indicate that the region's total applied agricultural water use will decrease by about 9 percent between 1990 and 2020. Improvements in on-farm irrigation operations and irrigation system technologies, the loss of irrigated land caused by urbanization, and minor shifts in crop type will contribute to the decrease. Table CR-7 shows increases of about 12,000 and 14,000 af in applied agricultural water use between 1990 and 2020 in the Twenty-Nine Palms and Borrego PSAs, respectively. During the same period, decreases of about 15,000 and 191,000 af are forecasted for both the Chuckwalla and Coachella PSAs, respectively.
Since the late 1970s, major efforts have been undertaken by local governments, water agencies, and growers to improve agricultural irrigation efficiency in the region. The most observable improvements have been made in the Imperial and Coachella valleys. Agricultural conservation in the region can be placed into two categories: (1) on-farm irrigation system management and operation improvements, and (2) conveyance system improvements. Examples of current on-farm improvements include: carefully managing and designing furrows, basin and sprinkler systems to minimize excessive tailwater runoff from the ends of fields into drains and to evenly irrigate the entire field; laser leveling of fields to improve irrigation water movement in furrows and basin systems; implementing micro-irrigation technology (drip emitters and micro-jet sprinklers) for permanent crops; using different irrigation and cultivation techniques (hand-moved sprinklers for pre-irrigation of fields and seed germination); reusing tailwater to supplement delivered water for the irrigation of other fields; and irrigation scheduling. Subsurface irrigation systems are also being tested on certain crops in the region.
Conveyance system improvements have come in the form of: constructing regulatory reservoirs to enhance system delivery and storage capabilities; lining canals and laterals with concrete to minimize supply losses due to seepage; automating the system with telemetry for improved control over the delivery of water; and installing seepage recovery and operational spill interceptor systems.
Total 1990 environmental water use for the Colorado River Region amounts to nearly 39,000 af. Demands are forecasted to increase 13 percent by 2000 and remain at 44,000 af through 2020. Colorado River water supplies most of this use. Currently, there are two major areas where water is used for wildlife habitat in the region: the Salton Sea National Wildlife Refuge and the Imperial Wildlife Area. There are also several private wetlands. Table CR-8 shows wetlands water needs in the Colorado River Region.
The Salton Sea National Wildlife Refuge was established in 1930 by federal executive order. Originally the refuge contained 23,425 acres, but due to inflow of agricultural drain water and a rise in the sea level, most of the refuge is now inundated. About 2,500 acres of manageable habitat remain, with about 1,068 acres managed as marsh land. In 1990, the refuge used about 4,900 af of freshwater. Forecasts indicate the refuge will require about 10,000 af of freshwater by the year 2000.
The Imperial Wildlife Area is operated and managed by the State Department of Fish and Game. The area is comprised of two units. The Finney-Ramer unit has a total water surface area of about 2,050 acres, with total annual water use estimated at 7,600 af. The Wister unit has a total water surface area of about 5,500 acres and total annual water use of almost 21,000 af. Demands are forecasted to remain level through 2020.
Private wetlands in the Colorado River Region occupy about 2,225 acres and consumptively use roughly 5,330 af of freshwater annually. These wetlands, scattered throughout Imperial and Riverside Counties, are primarily used for duck hunting.
Conveyance losses in the All-American, Coachella, and intermediate canals averaged about 360,000 af in 1990. Both the Imperial Irrigation District and Coachella Valley Water District conveyance losses are calculated as the acre-feet of water diverted minus the amount of water actually delivered to users by the districts. Conservation measures could reduce conveyance losses by 100,000 af per year. Geothermal power plants in Imperial Valley PSA produce about 379 megawatts per year and use about 74,200 af of cooling water annually in their operation. Table CR-9 shows the total water demand for this region.
Recreational facilities are found in all PSAs; most consist of campgrounds and parks where water is used for drinking, landscape, toilets, showers, and facility maintenance. Total water use in these areas amounted to almost 5,000 af in 1990. The Colorado River PSA accounted for about 3,000 af of that use. Recreation includes water skiing, boating, fishing, and swimming. Figure CR-6 shows water recreation areas in the Colorado River Region.
Colorado River Water Allocations. As a result of the 1964 U.S. Supreme Court decree in Arizona v. California, California's allocation of Colorado River water was quantified and five Lower Colorado River Indian tribes were awarded 905,496 acre-feet of annual diversions, 131,400 af of which were allocated for use in and chargeable to California pursuant to a later supplemental decree.
In 1978, the tribes asked the court to grant them additional water rights, alleging that the United States failed to claim a sufficient amount of irrigable acreage, called "omitted" lands, in the earlier litigation. The tribes also raised claims for more water based on allegedly larger reservation boundaries than had been assumed by the court in its initial award, called "boundary" lands. In 1982, the special master appointed by the Supreme Court to hear these claims recommended that additional water rights be granted to the Indian tribes. In 1983, however, the court rejected the claims for omitted lands from further consideration and ruled that the claims for boundary lands could not be resolved until disputed boundaries were finally determined. Three of the five tribes#Fort Mohave Indian Tribe, Quechan Indian Tribe, and Colorado River Indian Tribe#are pursuing additional water rights related to the boundary lands claims. A settlement may be reached soon on the Fort Mohave claim. The Quechan claim has been rejected by the special master on the grounds that any such claim was necessarily disposed of as part of a Court of Claims settlement entered into by the tribe in a related matter in the mid-1980s. The Colorado River Indian Tribe case was presented to the special master in early 1993. As with all claims to water from the main stem of the Colorado River and any determination by the special master, only the U.S. Supreme Court itself can make the final ruling.
Any Colorado River or Fort Mohave tribal claims granted for additional water rights would reduce the amount of water available to satisfy the fourth priority demands of MWDSC under the 1931 California Seven Party Agreement, which established priorities for use of California's entitlement. Any Quechan tribal claims granted for additional water rights would reduce the amount of water available to satisfy the third priority demands of the Coachella Valley Water District under this agreement because the Quechan Tribe receives Colorado River water under the Yuma Project Reservation Division's second priority. If all additional water rights claims were granted to the three Indian tribes, MWDSC could effectively lose up to 22,600 af and Coachella up to 45,200 af of their Colorado River supplies. The actual amounts to be granted, if any, are yet to be determined.
The Lower Colorado Water Supply Act. On November 14, 1986, the President signed the Lower Colorado Water Supply Act, Public Law 99-655, authorizing the U.S. Secretary of the Interior to construct, operate, and maintain a project consisting of a series of wells along the All-American Canal. The project would be capable of providing up to 10,000 af of water annually from ground water storage to indirectly benefit the City of Needles, the community of Winterhaven, the U.S. Bureau of Land Management, and other municipal, industrial, and recreational users in California with no or insufficient rights to Colorado River water. Under PL 99-655, the Imperial Irrigation District, the Coachella Valley Water District, or both, would exchange a portion of their Colorado River water for an equivalent quantity and quality of ground water pumped into the All-American Canal during years that unused apportioned water supplies are not available. The Lower Colorado Water Supply Project is now under construction and is scheduled for operation in 1994.
Effects of the Central Arizona Project on Colorado River Allocations. The Central Arizona Project, with an annual diversion capacity of 2,100,000 af, started delivering water in December 1985. All aqueduct facilities were completed in 1992 and about 1,034,000 af of water were diverted for municipal, industrial, and agricultural uses in Central Arizona in 1993. Deliveries are expected to increase to 1,500,000 af annually under full development, with the capability of up to 2,100,000 af when it is available and needed in the future.
When the Central Arizona Project begins diverting its full allocation of Colorado River water, California will be limited to its basic annual apportionment of 4,400,000 af when the Secretary of the Interior declares that a normal condition exists. Additional water can be and has been made available when the Secretary determines a surplus condition exists, or when one or both of the other Lower Division states (Arizona and Nevada) are not fully using their apportioned water. Since 1985, neither Arizona nor Nevada has used its full basic apportionment, and the Secretary of the Interior has allowed California to use surplus water or Arizona's and Nevada's apportioned but unused Colorado River water. These factors have allowed California to divert and consumptively use from 4,500,000 af to 5,200,000 af annually since 1985.
The availability of Colorado River water to California in 1993 was determined in the annual operating plan issued by the Secretary of the Interior in October 1992. The 1993 annual operating plan makes sufficient water available to supply all of California's reasonable beneficial consumptive use demands, but the plan contains a proviso that if the total mainstream consumptive use in the Lower Division states exceeds 7,500,000 af, the entity or entities responsible for the overuse will be required to compensate for such overuse by 1996.
Lining of the All-American Canal. The Secretary of the Interior (under PL 100-675 enacted in 1988) is authorized to line portions of the All-American Canal and the Coachella Canal, using funds provided by MWDSC, Coachella Valley Water District, and Imperial Irrigation District. As of December 1993, the U.S. Bureau of Reclamation was preparing a final Environmental Impact Statement/Report regarding lining a portion of the All-American Canal. Lining the canal or constructing a parallel canal from Pilot Knob to Drop Number 3, about 25 miles east of Calexico, would save roughly 67,700 af annually.
The draft EIS/EIR for the project identified a parallel concrete-lined canal as the preferred alternative. The final EIS/EIR is scheduled to be filed in 1994 and construction could begin in 1995. In addition, the U.S. Bureau of Reclamation released a draft EIR/EIS in January 1994 regarding lining another section of the Coachella Canal to reduce seepage by about 30,900 af per year. Thus, if both canals were lined, as much as 98,600 af of water could be made available for other uses.
Salinity Concentrations in the Colorado River. Salinity in the Colorado River varies from year to year because the river is subject to highly variable flows. As a result of high river flows from 1983 to 1986, releases from reservoir storage into the lower Colorado River were greatly in excess of the releases required for beneficial uses. These record high flows reduced salinity in the lower river. However, since 1987, with below-normal water supply conditions and fewer reservoir releases, salinity levels have again increased.
Like most western rivers, the Colorado increases in salinity from its headwaters to its mouth, carrying a salt load of about 9 million tons annually (measured at Hoover Dam). Roughly 50 percent of the river's salinity results naturally from salt in saline springs, ground water discharge into the river, erosion and dissolution of sediments, and evaporation and transpiration. About 37 percent of the salt load comes from agricultural return flows, which carry dissolved salts from underlying saline soils and geologic formations. The remainder of the salt load results from out-of-basin exports, reservoir evaporation, development of energy resources in the Upper Colorado River Basin, and other municipal and industrial uses.
In 1972, the seven Colorado River Basin states adopted a policy that while they would continue to develop the Colorado River water apportioned to each of them, they would work with each other to maintain salinity concentrations in the lower main stem of the Colorado River at or below the flow-weighted average annual salinity of 1972. Later that year, amendments to the Federal Water Pollution Control Act required that standards for salinity in the Colorado River be established. In 1973, the seven basin states created the Colorado River Basin Salinity Control Forum to establish criteria and develop a plan for implementing a salinity control program.
In 1975, all the basin states adopted the salinity standards set forth in the report Water Quality Standards for Salinity, Including Criteria, and Plan of Implementation for Salinity Control, Colorado River System, as recommended by the forum. The state-adopted and EPA-approved numeric criteria call for maintenance of average annual flow-weighted salinity concentrations of 723 milligrams per liter below Hoover Dam, 747 mg/L below Parker Dam, and 879 mg/L at Imperial Dam.
Because of changes in hydrologic conditions and water use within the Colorado River Basin, the forum reviews its implementation plan every three years. The most recent recommended revisions to the plan appear in the 1993 Review, Water Quality Standards for Salinity, Colorado River System. The revised implementation plan is designed to control enough salt to maintain the salinity criteria adopted in 1975 under a long-term mean water supply of 15,000,000 af per year. The 1993 proposed implementation plan includes:
The forum reported that average salinity concentrations for 1992 were 657 mg/L below Hoover Dam, 688 mg/L below Parker Dam, and 781 mg/L at Imperial Dam, which were all below the Forum's numeric criteria. It also reported that there was no reason to believe the criteria would be exceeded during the next three years. In fact, forecasts appearing in the 1993 review state, "The plan will control salinity levels so that, with long-term mean water supply conditions, salinity levels below Hoover Dam will be about 25 mg/L below the numeric criteria."
Salton Sea. The Salton Sea is a 35-mile-long, 12-mile-wide, 40-foot-deep, saline body of water. In 1924, the federal government, recognizing the sea as a depository for agricultural drainage waters, placed lands lying 220 below sea level in and around the sea in a public water reserve.
In 1968, California enacted a statute declaring that the primary use of the Salton Sea is for collection of agricultural drainage water, seepage, leachate, and control waters. In 1980, a local farmer wrote a letter to the State Water Resources Control Board alleging that the Imperial Irrigation District was wasting water to the sea and causing his land to be flooded. After an investigation by DWR and several hearings by the SWRCB, the board, in 1988, ordered IID to develop a plan to conserve 100,000 af of water per year by 1994. The order required IID to make water delivery and irrigation practices more efficient and included a reservation of jurisdiction regarding the possible future conservation of up to 368,000 af annually.
The order caused concerns that conservation measures would lower the sea's surface level and increase salinity concentrations at a slightly faster rate. The Salton Sea became increasingly saline between 1907 and 1934, largely because of high evaporation and reduced inflow of freshwater. Since 1934 the salinity has varied from 33,000 mg/L to 45,000 mg/L. Inflow from Imperial, Coachella, and Mexicali valleys for 1989, 1990, and 1991 was 977,000 af, 108,000 af, and 141,000 af, respectively. Irrigation return flows, precipitation (which averages less than 3 inches per year), and local runoff are the only fresh water supplies to the sea. As is common in arid environments, the equivalent of several years' rain may arrive in a single storm. With a watershed exceeding 8,000 square miles, a large storm can elevate the sea by one foot or more.
Agricultural drainage carries with it varying amounts of nutrients, mainly compounds of nitrogen and phosphorus, which encourage the growth of algae. Although algae are very productive and support the higher trophic levels, algae blooms in the upper water levels discolor the water and, upon death and decomposition, often cause temporary local anoxic conditions and produce obnoxious odors. Fish are occasionally killed by the temporary lack of oxygen. These conditions reduce the sea's aesthetic appeal and, to some extent, depress water-related recreation.
Recent attention has been focused on the source of the selenium found in the Salton Sea. The selenium content in the Colorado River water delivered to the Imperial and Coachella Valleys has been found to be about 2 parts per billion and reflects selenium contributions from tributaries to the main stem of the Colorado River in the Upper Colorado River Basin. The concentration of selenium in the sea water is about 2.5 ppb. As the result of a concentration of leachates from the soils irrigated with Colorado River water, higher levels of selenium concentrations in agricultural drains have been found. Although drainage water consists of components (for example, tile water, tail water, and seepage) carrying different concentrations of selenium, the mixing that occurs in the drain channels results in a selenium concentration of about 8 ppb.
The SWRCB has adopted a California Inland Surface Waters Plan with a performance goal of 5 ppb for selenium concentrations in agricultural drain channels. In an earlier action, the California Department of Health Services, concerned over the concentration of selenium in the tissue of fish in the sea, issued a health advisory that fish consumption by humans be limited to avoid any adverse health effects.
Four bird species residing in the Salton Sea area are potentially adversely affected by organochlorine pesticides. Such pesticides are mobilized from farm fields and transported to drains by tail water runoff. Resuspension of bottom sediments in the New and Alamo rivers and drains is another source of these pesticides. Twenty-three different organochlorine pesticides have been found in various types of biota in the Imperial Valley.
The average salt loading of inflow to the sea over the past 30 years has been 4.9 million tons per year. Since 1980, salinity concentrations have increased at a rate of 500 to 600 parts per million per year. As of December 1993, salinity levels in the Salton Sea were 45,000 parts of salt per million parts of water#saltier than ocean water, which averages 35,000 ppm.
Further increases in salinity could harm fish and wildlife and the recreational resources in the area. Salinity concentrations in the sea are forecasted to reach 50,000 ppm in the next 10 years, even without further conservation measures being implemented, which would increase the rate. It is not likely, even under the most favorable hydrologic conditions, that the salinity of the sea will return to concentrations below 40,000 ppm. On the other hand, occasional flooding has also adversely affected shoreline developments and recreation. The sea has maintained relatively stable water elevations for the past decade.
Since 1987, the Salton Sea Task Force, chaired by the State Resources Agency, has been studying these problems. This intergovernmental group's objective is to find a way to conserve water in the Salton Sea area while stabilizing the sea's salinity and water levels. Several plans have been proposed; however, all plans would incur substantial costs. The task force is continuing to explore various means of improving the financial feasibility of the plans and to seek some form of regional organization as a sponsoring entity to carry out and provide funding for preservation measures.
MWDSC Water Conservation Agreements. To compensate for the loss of Colorado River water under the Supreme Court decree in Arizona v. California, MWDSC is pursuing a number of programs to augment its supplies. In December 1988, MWDSC and Imperial Irrigation District signed the first of two agreements expected to make 106,110 af of conserved water available to MWDSC annually, except under certain limited circumstances, by implementing structural and nonstructural water conservation projects within IID's service area. The conservation measures to be used are: (1) concrete lining of existing earthen canals, (2) construction of reservoirs and canal spill interceptors, (3) installation of non-leak gates and distribution system automation equipment, and (4) on-farm management of irrigation water. MWDSC will furnish an estimated $222 million (1988 dollars) for the conservation projects. Increased conservation in the IID would reduce surface and subsurface fresh water inflow to the Salton Sea, thus shortening the time it takes for the sea's salinity concentration to increase. Of the funds provided by MWDSC, $23 million is for indirect costs including, among other items, environmental mitigation and litigation relating to the impact, if any, of the water conservation program on the water level or quality of the Salton Sea, the New and Alamo rivers, to the extent such costs are not reimbursable.
The Palo Verde Irrigation District signed an agreement with MWDSC for a two-year fallowing program involving 20,000 acres of land that could save 186,000 af of Colorado River water (93,000 af per year). The fallowing began August 1, 1992, and will end July 31, 1994. Program lands lying fallow in 1992 are required to lie fallow through July 31, 1994. MWDSC must use the water, which is being stored in Lake Mead, before the year 2000.
IID and MWDSC have considered, but have not yet implemented, a test fallowing and modified irrigation practice program to save up to 200,000 af of Colorado River water over a two-year period for MWDSC's use. Fallowing and modified irrigation of alfalfa would be conducted by Imperial Valley farmers on a voluntary basis for monetary compensation.
Water Banking Proposal. The U.S. Bureau of Reclamation has formed a technical work group with representatives from California, Arizona, Nevada, and the Colorado River Indian tribes to explore the merits and feasibility of banking water in Lake Mead for use by California, Arizona, Nevada, and the tribes. A banking proposal is being considered as a provision of proposed regulations being prepared by USBR for administration of Colorado River entitlements in the Lower Basin.
Yuma Desalting Plant. The high salinity of Colorado River water in past years led to protests from the Republic of Mexico and an agreement between the United States and Mexico. To enable the U.S. to comply with the agreement without depriving Colorado River basin states of any of their apportioned water, the Yuma Desalting Plant was authorized under Title I of PL 93-320 in 1974. The purpose of the desalter is to remove sufficient salts from irrigation drainage water from the Wellton-Mohawk Irrigation and Drainage District in Arizona to meet the established salinity control standards at the Northerly International Boundary when the treated drainage water is released into the river. At the Yuma Desalting Plant, the brine discharge is disposed of in a channel leading to the Santa Clara Slough in Mexico, and the treated water is blended with the remaining untreated drainage water and returned to the river. The Yuma Desalting Plant began operation at one-third capacity in May 1992. Due to high flows in the Gila River early in 1993, the plant was shut down in January 1993.
Under full operation, the desalter will be able to take about 98,000 af of drainage water and produce 68,500 af of water; this will be blended with about 10,000 af of untreated drainage water, so that a total of 78,500 af will be returned to the river.
Water budgets were computed for each planning subarea in the Colorado River Region by comparing existing and future water demand forecasts with the forecasted availability of supply. The region total was computed by summing the demand and supply totals for all the planning subareas. This method does not reflect the severity of drought year shortages in some local areas which can be hidden when planning subareas are combined within the region. Thus, there could be substantial shortages in some areas during drought periods. Local and regional shortages could also be more or less severe than the shortage shown, depending on how supplies are allocated within the region, a particular water agency's ability to participate in water transfers or demand management programs (including land fallowing or emergency allocation programs), and the overall level of reliability deemed necessary to the sustained economic health of the region. Volume I, Chapter 11, presents a broader discussion of demand management options.
Table CR-10 presents water demands for the 1990 level and for future water demands to 2020 and compares them with: (1) supplies from existing facilities and water management programs, and (2) future demand management and water supply management programs. Regional net water demands for the 1990 level of development totaled 4,124,000 af for average and drought years. Those demands are forecasted to decrease to 4,012,000 af by the year 2020, after accounting for a 35,000 af reduction in urban water demand resulting from implementation of long-term conservation measures and a 273,000 af reduction in agricultural demand resulting from additional long-term agricultural water conservation measures.
Urban net water demand is expected to increase by about 220,000 af by 2020, due to increases in population, while agricultural net water demand is expected to decrease by about 258,000 af. Environmental net water demands, under existing rules and regulations, will increase from 39,000 to 44,000 af annually as a result of increased allocation of water to wildlife refuges.
Average annual supplies, including 75,000 af of ground water overdraft, were generally adequate to meet average net water demands in 1990 for this region. However, during drought, present supplies are insufficient to meet present demands and, without additional water management programs, annual average and drought year shortages are expected to be about 115,000 and 139,000 af by 2020, respectively.
With planned Level I programs, average and drought year shortages could be reduced to about 56,000 and 69,000 af, respectively. This remaining shortage requires both additional short-term drought management and future long-term Level II programs depending on the overall level of water service reliability deemed necessary. Because of high priority rights to Colorado River water by such areas in the Palo Verde Irrigation District, the Coachella Valley, and the Imperial Valley, any future shortages in these areas are expected to be limited. However, this region also depends on exports from the Sacramento-San Joaquin Delta for a portion of its supplies. Shortages stated above are based on Decision 1485 operating criteria for Delta supplies and do not take into account recent actions to protect aquatic species in the estuary. As such, water supply shortages are understated for the areas which depend on Delta supplies.