Colorado River Board of California
[NOTE: This is a 39-page (in the original) analysis of the likely effects on the Salton Sea of proposed water conservation projects. These would result in reduced agricultural wastewater flows into the Sea. It was prepared at the request of the California Legislature. If no conservation projects additional to those already in operation as of December 1990 were implemented, the study predicts that by 2020 the lake level would be about -228.5 ft and its salinity would be 60,000 ppm. If projects to conserve an additional 250,000 acre-feet were implemented, the study predicts that in 2020 lake level would be -231.4 ft and salinity 79,600. Though not discussed in this report, if water reclamation projects in Mexico reduced flows in the New River from Mexico, the predicted salinities would be higher and predicted lake levels lower. No specific prediction is made as to what salinity would seriously damage the sport fishery. Some advantages of a slightly lower lake level are pointed out. S. Hurlbert, SDSU]
Saltinity of the
The Salton Sea (Sea) has been an important body of water in the Imperial and Coachella Valleys since its formation in 1905. The Sea was formed when the entire flow of the Colorado River discharged into the Salton Trough, a large depression in Southeastern California. At 228 feet below mean sea level, the Sea has the second lowest elevation in the United States, with Bad Water in Death Valley being the lowest.
Geological research indicates that huge freshwater lakes formed and then evaporated many times over several thousands of years. When filled, the lake surface extended from Coachella Valley southward over the entire Imperial Valley, to pour over a 36 foot high natural dam in Mexico. The natural dam was formed by Colorado River delta sediments depositing at the mouth of the Gulf of California near Cerro Prieto, Mexico.
Although the Sea itself has no priority to receive water from any source, agricultural drainage and storm water from the Coachella, Imperial and Mexicali Valleys perennially sustain the Sea. Today, the Sea supports endangered species, migratory bird habitat, sports fishing, boating, camping, and other outdoor recreation.
The Sea has been an influencing factor on the economic development of the region. Because of the Sea's function as a repository for agricultural drainage water, it has allowed the expansion of agriculture where it would not otherwise be possible. A viable agricultural economy is essential to maintain the water flow to the Sea.
The increasing salinity of the Sea and the cyclic nature of the water level in the Sea have been a source of concern for several years. Current salinity levels pose a threat to the artificially established fishery and could impact the associated recreational values. Changing water levels have impacted both urban and agricultural developments along its 105-mile shoreline. Periodic flooding of adjacent lands as the Sea level rises and the stranding of developments along the shoreline as the Sea level declines have created real challenges to local interests. These conditions have prompted numerous studies at the federal, state, and local levels seeking answers as to how best to control the salinity and the water level of the Sea.
As studies continue, another factor affecting the Sea, water conservation, has raised further questions as to the future of the Sea. The California Legislature requested that the Colorado River Board of California report on the current condition of the Sea and evaluate the impacts of water conservation measures on the Sea. This report is in response to that request.
FORMATION OF THE CONTEMPORARY SEA
Archeological evidence indicates that a lake existed in the Salton Sink at least two thousand years ago. The lake had a life of about 150 years before disappearing through evaporation as the water coming into the sink somehow was interrupted. A second lake, formed in 1050 A.D., had a life of about 100 years and a third lake, formed about 1220 A.D., survived for 150 years. Finally, a fourth lake existed for 70 years about 1492 A.D. preceding the current Sea. Evidence has been found of the existence of additional lakes based on at least six different shorelines stretching back 26,000 years.
The peculiar behavior of the Colorado River and the ephemeral lake in the Salton Sink can be explained by normal delta mechanics. As the Colorado River enters the Gulf of California, its swift flowing water meets stationary ocean water. Sediment suspended by river turbulence settles out and, after a long period of time, the sediment builds up to form a delta. When the delta becomes high enough, the river backs up and flows northward into the Salton Sink, where swift flowing river waters form a lake and then begin to enter relatively quiet waters in the lake. A natural delta in the lake forms, and the process repeats itself.
Each time the river switched from the Salton Sink to the Gulf of California, the lake found itself isolated without water inflow. The lake waters then evaporated, leaving behind large deposits of sediment and concentrated salt on the lake bed. Each version of the newly formed lakes would support freshwater plants and animals until evaporation exceeded inflow and rising salinity left only the most salt-tolerant organisms until the lake became dry.
The contemporary Sea was formed when a Colorado River diversion was breached near Yuma, Arizona in the summer of 1905, and the river began flowing unimpeded into the Salton Sink. Unusual winter floods on the Colorado River and its Gila River tributary breached the diversion works that the California Development Company used to divert water into an irrigation canal (Alamo Canal) to deliver river water to the Imperial Valley (Figure 1). Subsequent high flows through the breach thwarted repeated attempts to close the breach, and for 16 months the entire flow of the Colorado River, an estimated 24 million acre-feet, poured uncontrolled through the Mexicali and Imperial Valleys to the Salton Sink. Many unsuccessful attempts were made to close the breach and return the river to its original channel. Finally, the Southern Pacific Railroad, which acquired the bankrupt California Development Company, controlled the flow in March 1907 by dumping many trainloads of boulders from a trestle constructed over the canal turnout.
The reestablished lake was given the name Salton Sea. The Sea attained a maximum depth of 83 feet at an elevation of 195 feet below sea level (-195 feet), about 33 feet higher than its current level. At its maximum elevation, it covered more than 330,000 acres of land in the Imperial and Coachella Valleys.
Based on early chemical analyses of the Sea, conducted in 1907, the mineral content of the Sea was about 77 million tons, with a total dissolved solids (TDS) concentration of 3,550 parts per million (ppm). Only about one-seventh of this total salt content was derived from the Colorado River water that formed the Sea during the nearly two-year period of inflow. Flood water from the Colorado River, with a mineral content of less than 300 ppm, may have dissolved some additional salts enroute to the Sea. But most of the balance of the mineral content at that time was dissolved from the bed of the Sea. The dissolution of minerals from the bed of the Sea apparently continued for several years.
By 1914, the mineral content had increased to about 110 million tons. The relatively small inflow from 1907 to 1914 would have contributed only minor quantities of minerals. The rate of increase slowed gradually as the quantity of soluble minerals on the bed decreased, and probably ceased or became negligible within a few years after 1914. In 1920, the salt concentration of the Sea water was slightly higher than that of ocean water (35,000 ppm). The annual inflow of salts increased after the early 1920's due to increasing agricultural development in the Imperial and Coachella Valleys. The salinity of the Sea and its water surface levels were dependent on the interaction of the evaporation process with the volume of water in and flowing into the Sea. The initial filling period was followed by a period of sharp decline in water levels before irrigation return flows increased to the point that they, together with local storm runoff, began exceeding evaporation and the elevation of the Sea gradually started increasing.
Irrigation of farmland in the Imperial and Coachella Valleys is dependent upon drainage into the Sea. In 1924, the President of the United States, by Executive Order, withdrew all land below elevation -244 feet and placed it in a public water reserve. In 1928, additional lands were withdrawn by Presidential Executive Order and the water reserve was expanded to include all land below elevation -220 feet. In 1968, the State of California enacted a statute declaring that the primary use of the Salton Sea is for the collection of agricultural drainage water, seepage, leaching, and control waters. (Stats 1968, Ch. 392, Sec. Z.) Thus the Sea is formally recognized as a repository for agricultural drainage. Irrigation return flows maintain the Sea as a perennial lake.
The Salton Sea occupies the deepest part of the Salton Trough, whose lowest point is nearly 280 feet below sea level. The tributary drainage includes an area of about 8,400 square miles, including the Coachella, Imperial, and Mexicali Valleys. Surface inflow, principally irrigation return water, plus domestic and industrial waste water, seepage, and runoff are the major sources of the Sea's replenishment. Generally, more than 80 percent of the surface inflow comes from the Imperial Valley, about 10 percent from the Coachella Valley and another 10 percent from the Mexicali Valley. The New and the Alamo Rivers are the principal water courses in the Mexicali and Imperial Valleys. The Coachella Valley Stormwater Channel (a man-made extension of the Whitewater River) is the major water course in the Coachella Valley. In addition, more than fifty drains and ditches in the Imperial and Coachella Valleys empty into the Sea. This drainage system is needed to maintain a favorable salt balance in the irrigated lands by carrying away salt-laden agricultural drainage water to the Sea and also to prevent water logging of the cropped land. Other sources of inflow to the Sea include runoff from Salt Creek, San Felipe Creek and other minor tributaries, subsurface inflow and direct precipitation. In total, an average of about 1.3 million acre-feet (maf) of annual inflow reaches the Sea under current conditions.
By far the largest quantity of water now used in the Salton Sea Basin comes from the Colorado River. Water destined for Imperial and Coachella Valleys is diverted from the Colorado River into the All-American Canal at Imperial Dam, and water for the Mexicali Valley is diverted into the Alamo Canal at Morelos Dam, a mile downstream of the Baja California-California boundary.
Over 3 maf of Colorado River water are imported by the Imperial Irrigation District (IID) and the Coachella Valley Water District (CVWD) annually. About 86 percent is used in the Imperial Valley and 14 percent in the Coachella Valley. In addition, 1.5 maf of Colorado River water are delivered to Mexico annually, under the 1944 United States - Mexican Water Treaty, most of which is used in Mexicali Valley. In several recent years, excess arrivals of Colorado River water to Mexico have attained levels of more than 14 maf. During the four years of Colorado River excess releases, 1983-1986, Mexico received more than 45 maf. Some of these excess flows were diverted and used for irrigation and ground water recharge in the Mexicali Valley resulting in much higher discharges to the Sea.
Municipal water supplies for the Imperial Valley are obtained from IID canals distributing Colorado River water. In the Coachella Valley, all of the municipal water supplies are obtained from ground water. In addition to the Colorado River supply available for irrigation in the Mexicali Valley, Mexico also pumps groundwater for both irrigation and domestic use.
Irrigated agriculture has been practiced in the Coachella Valley using ground water since 1894 and in the Imperial Valley since 1901 by diversions from the Colorado River. IID was organized in 1911 to deliver Colorado River water to lands within the Imperial Valley for agriculture, domestic, industrial and other beneficial uses. By 1922, IID had acquired the properties of the defunct California Development Corporation from the Southern Pacific Company and the distribution canals from the mutual water companies. In 1932, IID contracted with the Secretary of the Interior for the delivery of Colorado River water for beneficial consumptive use as reasonably required for potable and irrigation purposes within the boundaries of IID. In 1942, IID began receiving all of its water from the All-American Canal, authorized under the Boulder Canyon Project Act of 1928.
CVWD was formed in 1918 for the purposes of protecting the existing ground water basin and to seek a supplemental supply for the valley because groundwater levels were dropping rapidly. In 1934, CVWD contracted with the Secretary of the Interior for the delivery of Colorado River water for beneficial consumptive use as reasonably required for potable and irrigation purposes within the Coachella Service Area as defined in the contract. The Coachella Branch of the All-American Canal, delivering Colorado River water via the All-American Canal system, was completed in 1948.
Irrigated agriculture in the Imperial and Coachella Valleys increased to over 500,000 acres in the mid 1970's. Currently the irrigated lands in the two valleys consist of about 520,000 acres, approximately 460,000 acres in Imperial Valley and 60,000 acres in Coachella Valley. Figure 2 depicts the Colorado River water diversions as measured at Pilot Knob on the All-American Canal for IID and CVWD.
Salton Sea State Recreation Area
The Salton Sea State Recreation Area, lying along the northeast side of the Sea, was opened in 1954. Developments are concentrated in five areas where a variety of recreation features are available to the public including picnic and camping facilities, boat ramps, boat moorings, a visitor center and concessionaire facilities. The developed areas include the Headquarters Area to the north, and Mecca, Corvina Beach, Salt Creek, and Bombay Beach to the south. Visitation at the State Recreation Area has varied greatly since its initial development. Annual visitation of more than 600,000 was experienced in the early 1960's shortly after the State Recreation Area was opened. Visitation peaks of over 400,000 annually occurred in the late 1970's and early 1980's. The current level of use, 1991, is estimated to be about 168,000 visitors.
National Wildlife Refuge
The Salton Sea National Wildlife Refuge was established in 1930 by Executive Order signed by President Herbert Hoover for the protection of waterfowl and other migratory birds. The refuge is located at the south end of the Sea. It is the southern-most refuge in the Pacific Flyway and the only national wildlife refuge located below sea level.
Originally, the refuge encompassed 23,425 acres comprised of nearly 60 percent open saline lake with the balance made up of shoreline alkali flats, freshwater marshes, native desert scrub, and farm fields. Later in 1947, IID leased an additional 24,000 acres to the California Department of Fish and Game, the U.S. Navy and the U.S. Fish and Wildlife Service (USFWS) in order to expand the refuge.
The refuge is generally flat. Due to the inflow of agricultural drainwater from the surrounding land and a subsequent rise in the level of the Sea, all of the original 23,425-acre refuge area has now been inundated. Much of the leased land is flooded. At present, only about 2,500 acres of manageable habitat remain, with 1,040 acres suitable for farming and 1,068 acres managed as marsh. The majority of the remaining 400 acres is composed of dikes, shoreline, and salt flats with some potential reclamation as freshwater marsh habitat.
Management emphasis is placed on the maintenance and improvement of wintering goose and duck habitat. Protection and enhancement of wetland habitat for the endangered Yuma clapper rail and maintenance of habitat for nesting and migratory populations of marsh birds and shorebirds also are major objectives.
Imperial State Wildlife Area
In 1954, the Imperial State Wildlife Area was formed in order to safeguard habitat for migratory birds, alleviate crop damage to adjacent farms and offer some unique recreational opportunities. The Western Unit of the Wildlife Area encompasses over 5,000 acres, all located 200 feet or more below sea level. The Sea forms the entire western boundary. More than 400 different species of wildlife are found occupying seasonally flooded ponds and fields formed by 189 miles of levees and 27 miles of canals. The Wildlife Area provides freshwater marsh habitat for other migratory birds using the Pacific Flyway.
Agricultural development in the Imperial and Coachella Valleys is the single-most important factor influencing the economic well being of the area surrounding the Sea. The annual gross farm revenues of IID and CVWD for Calendar Year 1990 were $1 billion and $347 million, respectively.
The Sea is an attraction for recreation use drawing visitors from much of southern California and portions of central California according to research conducted by CIC Research, Inc. for the California Department of Fish and Game. Fishing was reported as the most important motive for visiting the Sea, followed by camping, picnicking and boating. CIC estimated in 1987 that the Sea supported a total of more than 2.6 million recreation use days annually and that Sea-related expenditures in the local area were in the range of $99 million annually with additional multiplier benefits of $296 million regionwide.
Developments along the west shore of the Sea in Imperial County constitute the most concentrated urban area near the Sea. The communities of Desert Shores, Salton Sea Beach, Vista del Mar, and Salton City, covering an area of more than ten square miles, support a permanent population of about 3,000. The area supports many more during the peak recreation season. Other urban/recreation developments lie along the north and southeastern shore of the Sea in Riverside and Imperial Counties. The community of North Shore Beach Estates, in Riverside County, lies at the north end of the Sea. The community of Bombay Beach, with a permanent population of about 400, is located on the east shore of the Sea in Imperial County. Southeasterly of Bombay Beach, a number of small developments have been established along the mineral hot springs formed by the San Andreas Fault about six miles east of the Sea.
The quality of water in the Sea was first influenced by the quality of the inflowing Colorado River water during 1905-1907 and the subsequent dissolution of minerals from the bed of the Sea. With limited natural inflow to the Sea and modest levels of irrigated agriculture until the early 1920's, the Sea level dropped rapidly because of evaporative losses with a corresponding increase in salinity concentrations to about 40,000 ppm of TDS in the mid- 1920's (Figure 3).
Salinity increased to about 43,000 ppm in the mid-1930's, as a result of a decline in volume of the Sea caused by a shortage of irrigation water in 1931-35. A subsequent increase in volume counteracted the continuing increase in mineral content and caused salinity to decline to about 34,000 ppm in the early 1940's. Salinity has steadily increased since then, fluctuating between 32,000 and 44,000 ppm.
The total dissolved mineral content in the Sea presently mexceeds 400 million tons and is increasing at a rate of nearly 5 million tons per year. This rate of increase can be expected to continue for the foreseeable future. The salinity concentrations will continue to vary as a function of the volume of water in the Sea which reflects the balancing between inflow and evaporative losses.
The slow changes in elevation and salinity tend to obscure the massive dynamics of the Sea. At its current level, the Sea, holding 7.5 maf of water, loses about 17% of its volume every year to evaporation, and this is being replaced with 1.3 maf of inflow to the Sea. If agricultural production, and hence irrigation, were to cease in the Imperial, Coachella, and Mexicali Valleys, this 17% loss would not be replaced, representing an equivalent increase of about 7,600 ppm in salinity over the current 44,000 ppm concentration in one year.
INFLOW TO THE SEA
Surface water reaching the Sea is collected in the region's three main watercourses - the New River, the Alamo River, and the Coachella Valley Stormwater Channel. In addition, over thirty drains in the Imperial Valley and twenty-one drains from Coachella Valley discharge directly to the Sea. The New and Alamo Rivers convey drainage water and runoff from Mexico to the Sea. The New River also conveys industrial, human and slaughterhouse waste from Mexico to the Sea. The Alamo River conveys artesian water from the east side of the Imperial Valley. Because of annual variations in rainfall and cropping patterns, and the addition of conservation and diversion projects, inflow to the Sea has varied widely over the years. Inflow from Imperial, Coachella, and Mexicali Valleys for the period 1989-1991 averaged 977,000, 108,000, and 141,000 acre-feet, respectively. Other surface water channels contributing natural runoff to the Sea are San Felipe Creek, which enters the southwest end of the Sea, and Salt Creek, which enters the Sea along the northeast shore. These two channels carry about one-half of the surface water inflow that comes from the smaller drainage areas surrounding the Sea other than in the Imperial and Coachella Valleys. The remainder of the surface inflows to the Sea is contributed by minor channels discharging directly into the Sea, some of which is artesian water intercepted in the Coachella Valley.
Most of the Sea drainage area receives less than 3 inches of rain per year. Rain falling directly on the Sea is relatively insignificant considering the annual evaporation losses of 5.8 feet per year. The precipitation that does occur in the area results from storms of two types - general winter storms and convection summer storms. However, 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, this type of storm can elevate the Sea by one foot or more.
The Sea and its surrounding area are underlain largely by relatively impermeable lake deposits which overlie thick alluvial sediments. This is especially true in the Imperial Valley where the low permeability of these materials is indicated by the low yields of wells near the Sea. In the Coachella Valley, the sediments are more permeable as indicated by the higher yields of both artesian and non-artesian wells.
In comparison to surface inflow, ground water recharge of the Sea is a small component of the total inflow. Groundwater inflow to the Sea is estimated to be 50,000 acre-feet per year. Of this total, about 30,000 acre-feet are contributed by the Coachella Valley where surfacing artesian water is intercepted by tile drains. About 2,000 acre-feet is contributed by the Imperial Valley. About 10,000 acre-feet enters through the alluvium bordering San Felipe Creek, and the remaining 8,000 acre-feet enter through the alluvium in other peripheral areas.
A geothermally-active region of the Imperial Valley lies to the southeast of the Sea near the mouth of the New and Alamo Rivers. A number of wells have been drilled to tap the geothermal resources at depths ranging from 2,000 to more than 8,000 feet with brines reported with solids content in the range of 35,000 ppm to 370,000 ppm and temperatures in the range of 300 to 600 degrees Fahrenheit. The full extent of the resources are not known; however, they can be developed for power or the brine processed for chemical production. The discharge to the Sea of waste brines from either of these operations is prohibited by the California Regional Water Quality Control Board (Colorado River Basin Region) Resolution No. 63-14 and subsequent resolutions.
SEA LEVEL FLUCTUATIONS
During the initial filling in l905-07, the Sea rose to a water surface elevation of -195 feet with a depth of 83 feet. However, the Sea water depth and surface area began reducing steadily under evaporation losses which greatly exceeded inflow to the Sea during that time. The Sea then stabilized for several years at about -250 feet (Figure 3). From the mid-1920's, the Sea level began a generally increasing trend, largely reflecting increased crop acreage coupled with the installation of an extensive drainage system in Imperial Valley required to maintain a salt balance within the soil profile. The Sea level continued to rise until evaporation from the surface area equalled the inflow. During the late 1970's and the early 1980's, heavy runoff in the Colorado River resulted in excess river water reaching Mexico where increased diversions were made to satisfy expanding agricultural development in Mexicali Valley and reduce ground water pumping. Agricultural drainage increased and, for a period of six years, 1983-1988, nearly doubled the discharge to the Sea through the New and Alamo Rivers (Figure 2). These increased flows from Mexico, coupled with above average precipitation in the Salton Sea Basin during this period, contributed to raising the Sea's elevation about three feet over the level it had maintained for the preceding 20 years. An elevation of -226.0 was reached in 1984, the highest elevation the Sea had attained after its formation. Homes, businesses and farm fields were flooded bringing about litigation. During the last few years, the Sea elevation has gradually declined. The elevation of the Sea in December 1991 was about 1 foot lower than in December 1984 reflecting the near balance between evaporative losses and the present magnitude of inflows.
Factors influencing inflow to the Sea and water level fluctuations are mostly related to the continued use of Colorado River water in the Imperial and Coachella Valleys and to a lesser degree the amount of drainage water and other surface flows from Mexico. Over the past ten years, the diversion of Colorado River water to serve irrigated lands in the Imperial and Coachella Valleys has ranged from a low of about 2.9 maf (1983) to 3.4 maf (1990). Any significant reductions in inflow to the Sea would be related to changes in the area of lands irrigated, changes in cropping patterns influencing seasonal irrigation needs, and water conservation practices. The effects of current and possible future conservation measures on the Sea are discussed under the heading "Effects of Water Conservation Measures".
SALINITY OF THE SEA
Evaporation of the tremendous volume of water from prehistoric lakes left large deposits of soluble minerals on the dry surface in the Salton Sink. Much of the mineral residues were redissolved when water again collected in the Sink. Because of the presence of these soluble minerals, the Sea became a saline body of water soon after its formation, even though it was formed by a flood of fresh water from the Colorado River. This change is an entirely natural progression repeated in closed desert basins throughout the world.
The salinity of the Sea at any specific time is a function of the total quantity of dissolved salts in the Sea and the volume of water in the Sea at that time. Early records show that the salinity of the Sea exceeded 40,000 ppm at three different times in the recent past, the mid-1920's, mid-1930's, and in 1969 (Figure 3). If the current volume of the Sea were to remain relatively constant, the annual salt loading of 4.9 million tons would increase the salinity concentration at a rate of about 550 ppm a year. Because the Sea lies in a closed basin with no outlet for the removal of salt, the salt content will continue to increase as long as inflow to the Sea continues. As recent history has shown however, the salinity concentrations will vary, depending mainly upon the amount of water in the Sea.
Salinity records also show that there are annual fluctuations in salinity, measured in May and in November, that are related to the annual fluctuations in Sea elevations which are approximately one foot higher in May than those measured in November. The order of magnitude of the annual salinity differentials has been about 1,500 ppm in the last few years.
The California Regional Water Quality Control Board, Colorado River Basin Region, states in its May 1991 Water Quality Control Plan, Colorado River Basin Region, that it is unreasonable for it to assume total responsibility for implementation of its objective to reduce the present level of salinity and stabilize it at 35,000 ppm. The Water Quality Control Plan states that the achievement of this water quality objective is to be accomplished without adversely affecting the primary purpose of the Sea which is to receive and store agricultural drainage, seepage, and storm waters. The Water Quality Control Plan indicates that 35,000 ppm may not be realistically achievable. In such case, any reduction in salinity which still allows for survival of the Sea's aquatic life shall be deemed an acceptable alternative or interim objective.
Quality of Inflow
The salinity of water flowing to the Sea is determined mainly by the salinity of Colorado River water at Imperial Dam where it is diverted for use in the Imperial and Coachella Valleys. The salinity also depends on the irrigation pattern, the salinity of the tailwater and the water (leaching water) contributed to the agricultural drains, and the salinity of the municipal and industrial return flows.
The salinity of the Colorado River dropped significantly between 1983 and 1986 when, during the 4-year period of high flows on the Colorado River, the quality of water in the Colorado River reservoir system was significantly improved. Since 1986, the salinity of Colorado River water at Imperial Dam has increased to a level now approaching the pre-1983 period and is expected to continue increasing gradually. The average annual flow weighted salinity of Colorado River water at Imperial Dam for the 24 year period 1959-1982 was 831 ppm. By contrast, the average annual salinity at Imperial Dam for the period 1983-1991 was 668 ppm, a reduction of 163 ppm. Figure 4 depicts the annual flow weighted salinity of the Colorado River at Imperial Dam since 1959. This improved quality of Colorado River water contributed to reducing the salt loading to the Sea during this period. It is estimated that the salinity of the Sea would have been more than 300 ppm greater than the actual value recorded in 1991 without the improved quality of the Colorado River water. No significant reduction in the salinity at Imperial Dam is expected in the near future.
The salt loading of the Sea during the period from 1960 to 1982 averaged about 4.9 million tons per year. During the past ten years, 1982 to 1991, however, the average salt loading decreased to about 4.4 million tons per year, reflecting primarily the improved quality of Colorado River water used in the Imperial and Coachella Valleys (Figure 5). The long-term salt loading of the Sea is expected to more likely continue at a rate of 4.9 million tons per year.
A 1972 amendment to the Federal Water Pollution Control Act (P.L. 92-500), now commonly known as the Clean Water Act, required that water quality standards be established for the Colorado River including numeric salinity criteria. Numeric criteria were subsequently established by the Colorado River Basin Salinity Control Forum at three stations on the Colorado River, including one at Imperial Dam. The criteria and plan of implementation have been adopted by each of the Colorado River Basin states and approved by the Environmental Protection Agency (EPA). The numeric criterion set for Imperial Dam is 879 ppm. The Colorado River water supply to the Imperial and Coachella Valleys can be expected to be maintained at or below that level.
Irrigation return flows from applied Colorado River water constitute the Sea's major source of replenishment, largely through the New and Alamo Rivers and to a lesser extent, the Coachella Valley Stormwater Channel. The quality of the water from these sources varies from approximately 2,500 ppm TDS to 3,500 ppm TDS. Minor tributaries, such as San Felipe Creek, which produce inflow to the Sea largely as flood runoff, contain water with mineral contents in the 7,000 to 9,000 ppm TDS range.
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 anoxic conditions locally 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 contact recreation. The fishery, however has flourished on the bountiful food supply.
The presence of selenium in the Sea area has recently focused attention on its source or sources. The selenium content in the Colorado River water delivered to the Imperial and Coachella Valleys has been found to be in the 2 parts per billion (ppb) level and reflects selenium contributions from tributaries to the mainstem of the Colorado River in the Upper Colorado River Basin. The concentration of selenium in Sea water is about 2.5 ppb. Selenium concentrations in agricultural drains have been found at higher levels. Although drainage water consists of components (tile water, tailwater, seepage, etc.) carrying different concentrations of selenium, the mixing that occurs in the drain channels results in a selenium concentration of about 8 ppb. Higher levels of selenium in the drains are the result of a concentration of the leachates from the soils irrigated with Colorado River water.
The State Water Resources Control Board (SWRCB) has adopted a California Inland Surface Water Plan with a performance goal of 5 ppb for selenium concentrations in agricultural drain channels. In an earlier action, concerned over the concentration of selenium in the tissue of fish in the Sea, the California Department of Health Services issued a health advisory that fish consumption by humans be limited to avoid any adverse health effects.
The original fish population in the Sea consisted mainly of the same species found in the Colorado River. This population was swept into the Salton Sink during flooding when the Sea was formed in 1905-1907. There is also evidence that some fish from the Gulf of California migrated upstream during the flooding. Because very little inflow was entering the Sea after 1907 when the Colorado River was returned to its channel, the high evaporation rates caused the Sea to decrease in size rapidly resulting in an associated increase in salinity. The resultant rapid increase in salt concentrations quickly eliminated all native fresh water fish species, except for the desert pupfish, and severely depleted the populations of the saltwater species.
During the 1929-1950 period, several unsuccessful attempts were made to develop a sport fishery in the Sea. During the succeeding years through 1956, several saltwater species were introduced by the Department of Fish and Game (DFG). Resident species today consist of three game varieties: orange mouth corvina, sargo, and gulf croaker (bairdiella). Other fish presently in the Sea include tilapia, threadfin shad, mosquito fish, long-jawed mudsucker, and sailfin molly.
As part of its development of the fishery, DFG also introduced several species of invertebrates to provide food for some of the fish. Except for the corvina, which preys on the sargo and gulf croaker, the other fish species rely directly on these invertebrates for a major portion of their food supplies. The invertebrates, in turn feed mainly on detritus in the bottom sediments, as well as plankton. The Sea fishery is a very unitary type of ecosystem in that if one species fails, there are no alternative branches to bypass that vacant link in the food chain, thus the entire ecosystem could fail quickly.
Fresh water species have been noted in the Sea at times at its southerly extremes. They most likely enter via the New and Alamo Rivers as well as directly from agricultural drains. The species include carp, sunfish and catfish. They appear to remain for only short periods of time, retreating back into the rivers or canals.
Estimates of angling use at the Sea have varied widely over the years and are currently considerably lower than those estimated by CIC Research, Inc. in its 1987 surveys. The decline in angler use over the past few years reflects the stress on the fishery as a result of the increasing salinity levels and other factors affecting the food chain.
Sensitivity to Salinity
Salinity concentration is the most important single factor in the determination of whether the fishery in the Sea will continue to remain as it is today or change. Earlier research completed in 1974 by DFG concluded that adult fish can tolerate somewhat higher concentrations than larvae and young fish. These studies showed that at salinity concentrations at or near 40,000 ppm, reproduction of game species will decline as a result of egg and larval mortality. Older fish will survive but grow less desirable as game fish. Studies completed in 1983 by DFG confirmed that the concentration of 40,000 ppm is probably critical to the Sea's fish population. The DFG stated that adult die-off would reach major proportions if the salinity concentration reaches 50,000 ppm.
Because these studies were conducted over a short duration, there is the possibility that fish in the Sea may adapt to higher salinity levels if the increase occurred gradually over a longer period of time, presumably several generations. More recent DFG studies completed in 1989-1990 indicate that while the 40,000 ppm salinity barrier to egg and larval survival may be somewhat low, considering that the Sea salinity over the past 4 years has been in the range of 40-44,000 ppm, reproductive failure may be close at hand. As adults are tolerant of salinities greater than 50,000 ppm, they may exist for many years in the Sea but will decrease by attrition. The attrition of orangemouth corvina, a long lived species, will probably be hastened by the early attrition of bairdielia, a short lived species that serves as a prey fish along with non-existent juveniles of sargo and orangemouth corvina.
Another water quality issue that can affect the existence of a fishery in the Sea is eutrophication which has been observed in the Sea at times. Eutrophication is the process by which a body of water becomes, either naturally or by pollution, rich in dissolved nutrients (such as phosphates), and demonstrates a seasonal deficiency in dissolved oxygen. Eutrophic conditions in the Sea generally manifest themselves most visibly in shallow waters when the algae population blooms. If severe enough, the algae use up the oxygen and adverse effects on the fishery can result. Aesthetic problems in the form of odors can also reduce the value of the Sea as a recreational resource. It is generally believed that the cause of these conditions is a direct result of a combination of nutrients entering the Sea from inadequately treated sewage and drainage from agricultural lands. Because the blooms tend to be cyclic in nature, however, they are not regarded as being as serious a problem as salinity.
The Salton Sea National Wildlife Refuge includes large open-water areas, saline wetlands, and uplands. The Sea is of particular value for wildlife. It is a major stopover for many species of migratory waterfowl and shorebirds utilizing the Pacific Flyway. In many respects the marshes along the Sea have offset the reduction of those of the Colorado River delta which have diminished with the diversion of Colorado River water.
The Wildlife Refuge is especially noted for its variety of bird life. More than 372 species of birds have been documented at the refuge and in the adjacent Imperial Valley. More than 90,000 migratory waterfowl currently use the refuge each winter, including approximately 30,000 Canada and snow geese and 60,000 ducks. The predominant duck species at the refuge is the ruddy duck, whose wintering population of 42,000 represents 49 percent of the total number of this species found in the Pacific Flyway. Migratory waterfowl usually arrive in November and remain through February.
In addition to migratory waterfowl, many species of colonial nesting birds use the refuge and adjacent wetlands. In 1987, surveys indicated that at least 250 great blue herons, 16,000 cattle egrets, and 100 great and snowy egrets were nesting in the area. Winter populations of fish-eating birds include 33,000 white pelicans, 2,400 double-crested cormorants, and over 65,000 eared grebes that use primarily the open-water areas of the refuge. Large numbers of black-necked stilts and other shorebirds use the Sea marshlands and unvegetated shallow-water habitats as wintering, nesting, and rearing areas. Endangered species in the area include the desert pupfish, Yuma clapper rail, bald eagle, peregrine falcon, and California brown pelican. Other sensitive species occasionally using the refuge include whistling ducks, wood stork, long-billed curlew, mountain plover, and white-faced ibis.
The Salton Sea National Wildlife Refuge, originally created for migratory waterfowl, has evolved into an important recreational asset to the area. Because of the diverse variety of birds, recreational bird watching has, in recent years, become a major use of the refuge area. Some hunting of migratory waterfowl occurs on lands adjacent to the refuge.
Since 1985, the refuge annually has purchased about 2,000 acre-feet of Colorado River water from IID for the active management of 500 acres of wetland and cropland to support wintering migratory waterfowl. Additional efforts to increase the carrying capacity for waterfowl and shorebirds through the purchase of Colorado River water are currently underway. Since 1979, dikes have been constructed to protect parts of the refuge and reclaim small parcels of formerly inundated wetlands.
U.S. Department of Interior studies indicate that selenium and boron are at or approaching levels of concern to waterfowl and fish in the Sea areas. Boron concentrations in migratory waterfowl are at levels that could cause reproductive impairment, and selenium levels in waterfowl and fish are approaching levels of concern. Mercury levels in Sea waterfowl are also elevated, but there is no indication that the mercury in these migratory species comes from Colorado River sources. Organochlorine pesticide residues are currently detected in bottom sediments in local drains, possibly causing reproductive impairment in waterfowl and piscivorous birds.
WATER CONSERVATION MEASURES
The IID began its water conservation efforts in the mid-1950's by lining earthen canals, and installing seepage recovery systems along the All-America Canal. In the 1960's, the pace of the lateral canal lining program was intensified and seepage recovery systems were installed along the East Highline Canal. In July 1976, IID, by Board Resolution 45-76, established a 13-point program aimed at conserving water. Although the provisions of the 13-point program called for implementing specific water conservation measures, the program did not establish a comprehensive water conservation plan. A tailwater assessment program was introduced in 1976 to conserve additional water. Under the program, farmers are triple charged for water diversions if the tailwater runoff, as measured by IID zanjeros at the tailwater delivery box, is greater than 15 percent of the ordered flow. Four regulating reservoirs were constructed in 1976, 1977, 1982, and 1983 to reduce operational losses. More than 900 miles of canals were lined prior to 1985.
The CVWD began its water conservation efforts in 1919 with the construction of percolation basins in the Whitewater River. The basins were designed to capture stormwater runoff rather than allow it to discharge to the Salton Sea. The current CVWD system delivering Colorado River water is operated by a network of microwave telemetry linked to automated computer controls. The 485 mile distribution system is entirely concrete lined. All delivery points have totalizing meters and water measurements are accurate to within 2%. The 1,500 ac-ft concrete lined terminal reservoir (Lake Cahuilla) at the end of the Coachella Canal brings system storage to approximately 2 acre-feet for every 40 acres.
Recognizing that the construction of modern irrigation facilities can occur on "either side of the water meter", over 250 private irrigation reservoirs have been constructed. Over 40% of the Coachella Valley is now irrigated under drip irrigation. Tailwater disposal was expressly declared an illegal activity in the 1950's, and is prohibited.
In 1980, the U.S. Bureau of Reclamation completed the construction of a concrete lined canal alongside the first 49 miles of the 87-mile earthen Coachella Canal which supplies Colorado River water to the Coachella Valley via the All-America Canal. The canal lining project was authorized under Title 1 of the Colorado River Basin Salinity Control Act (P.L. 93-320) for the purpose of reducing canal seepage more by as much as 132,000 acre-feet of water annually.
State Water Resources Control Board Requirements
On June 17, 1980, Mr. John J. Elmore, a farmer in Imperial Valley, filed an application with the California Department of Water Resources (DWR) requesting DWR to investigate the misuse of water by IID. DWR investigated Mr. Elmore's allegations against IID and determined that certain water losses occurring within IID's water supply and distribution facilities could be reduced or prevented. DWR estimated that IID could save 368,000 acre-feet of water annually through implementation of conservation measures within its service area and an additional 70,000 acre-feet by lining the All-American Canal from Pilot Knob to the East Highline Canal.
The DWR referred the matter to the SWRCB. The SWRCB took two actions: in June 1984 the Board issued Decision 1600 which found that 367,900 acre-feet of water could be conserved in Imperial Valley, and that IID should initiate water conservation projects. Then, finding compliance with Decision 1600 not proceeding satisfactorily, the SWRCB ordered (Order 88-20, 1988) that IID conserve at least 100,000 acre-feet of water by January 1, 1994, and that 20,000 acre-feet per year of the 100,000 acre-feet program be conserved by January 1, 1991. In addition, the SWRCB viewed the 100,000 acre-foot conservation effort as an initial step in a process that could conserve up to the identified 367,900 acre-feet per year.
IID/MWD Water Conservation Agreement and Approval Agreement Provisions
Following years of negotiations, IID and MWD entered into a water conservation agreement in 1988. The Conservation Agreement became effective in December 1989 after receiving the approval of CVWD and Palo Verde Irrigation District (PVID). The agreements call for MWD to bear all the costs of 15 different conservation projects that IID is implementing. The capital costs of the conservation program are estimated in 1988 dollars to total $97.8 million. Indirect costs total $23 million. The indirect costs are to cover costs and potential obligations related to the conservation of water which include, among other things, loss of hydroelectric power revenue, mitigation of adverse impacts on agriculture from increased salinity in the water, loss of revenues from reduced water deliveries, and environmental mitigation and litigation relating to the impact, if any, of the program on the water level or quality of the Sea to the extent such costs are not reimbursable by insurance. The annual direct costs are estimated in 1988 dollars to total $2.6 million upon full implementation of the program. In return, MWD will be entitled to divert from the Colorado River a quantity of water equal to the amount of water conserved by the conservation and the augmentation projects, estimated in 1989 to total 106,110 acre-feet per year upon full implementation of the program, and for at least 35 years thereafter, except under certain limited conditions specified in the 1989 Approval Agreement. Table 1 lists the 15 projects and the two additional augmentation projects and the estimated amounts of water conserved by each project through December 1991. The verification of water conservation is being carried out by a water conservation measurement committee consisting of representatives from IID, MWD, CVWD, and PVID and a chairman selected by the four agencies.
Potential and Plans for Additional Conservation
Preliminary discussions between IID and MWD for a second conservation agreement to conserve additional water in the Imperial Valley are underway. Estimates of additional water to be conserved are on the order of 150,000 acre-feet per year. Determining the impacts of additional conservation measures and indirect costs associated with a second conservation agreement are among the issues that the two agencies are trying to resolve by identifying mutually agreeable cost effective solutions.
TABLE 1 PROJECT Implementation
Completed 1. Trifolium Reservoir 2. South Alamo Canal Lining, Phase
3. South Alamo Canal Lining, Phase II
4. "Z" Reservoir (Bernard Galleano
Reservoir) Implementation in
Progress 5. Trifolium Interceptor 6. Lateral (Plum-Oasis) Interceptor
7. Lateral Canal Lining 8. Twelve-Hour Delivery 9-11. Vail, Rositas, and Westside Main
Canal Lining 12. Non-Leak Gates 13. Modified East Lowline Interceptor
14-15. Irrigation Water
Management 16. System Automation 17. Sperber Outlet a
WATER CONSERVATION PROGRAM PROJECTS
WATER TO BE
THRU DECEMBER 1991
1. Trifolium Reservoir
2. South Alamo Canal Lining, Phase Ia
3. South Alamo Canal Lining, Phase II
4. "Z" Reservoir (Bernard Galleano Reservoir)
Implementation in Progress
5. Trifolium Interceptor
6. Lateral (Plum-Oasis) Interceptor
7. Lateral Canal Lining
8. Twelve-Hour Delivery
9-11. Vail, Rositas, and Westside Main Canal Lining
12. Non-Leak Gates
13. Modified East Lowline Interceptor
14-15. Irrigation Water Management
16. System Automation
17. Sperber Outlet
a Augmentation Project
In 1988, P.L. 100-675 was enacted authorizing the Secretary of the Interior to line a portion of the remaining unlined section of the Coachella Canal and that portion of the All-American Canal from Pilot Knob to Drop 4. An estimated 30,000 acre-feet of water per year would be conserved by lining the remainder of the Coachella Canal and 67,700 acre-feet of water would be conserved by lining the All-American Canal from Pilot Knob to Drop 3.
EFFECTS OF WATER CONSERVATION MEASURES
As discussed in this report, the dynamics of the Sea are complex with the two most dominant factors affecting the Sea and its environs being the continuing increase in salt content affecting its salinity and the varying water elevations posing the possibility of either flooding or shoreline recession. Past water conservation practices have influenced these factors, and future conservation measures will result in further change. This section discusses the effects of past and future conservation measures on the Sea and its environs.
Water conservation practices over the past four decades have influenced the current characteristics of the Sea. While the past conservation measures began in modest proportions, they currently represent an estimated 100,000 acre-feet of reduced inflow to the Sea annually. Had these measures not been taken, an analysis of the past activity indicates that the Sea, today, would have been about three feet higher and the salinity concentration about 4,000 ppm lower.
To evaluate the effect of future water conservation measures on the Sea, it was assumed that the conservation measures in place as of December 31, 1990 would represent the "current level case" against which further conservation developments would be compared. The current level case and the comparative studies reflect the salinity concentration (43,200 ppm) and elevation of the Sea (-227.8 feet) on that date as the common starting point. Com- parisons of this current level case were made with two levels of additional conservation. The first additional level of conservation consists of the program under the IID-MWD Agreement (100,000 acre-feet) which will be fully implemented by 1995 (Case A-1) and the second additional level is based on the assumption of implementing a subsequent phase to conserve another 150,000 acre-feet over a period of five years beginning in 1995 (Case A-2).
These comparative studies were made utilizing projections of hydrologic conditions and agricultural use patterns in the United States and Mexico based on average values experienced over the past thirty years. Projections of Sea elevations and salinity concentrations through the year 2020 for the two levels of additional conservation were compared to the current level case.
Figure 6 depicts the projections of future elevations of the Sea for the current level case and the two additional levels of conservation. These projections were based on future inflow patterns reflecting average conditions for the period 1960-1988 adjusted for conservation and a flow from Mexico during that period averaging 125,000 acre-feet per year. For the current level case, the elevation of the Sea is projected to drop gradually over the next 30 years about 1 foot to a level approaching -228.5 feet. Under Case A-1, the elevation of the Sea in the year 2000 would be about one and two-thirds feet lower than at present, or -229.4 feet, lowering to about -231.4 feet in the year 2020.
As the projections depicted on Figure 6 were based on average future conditions, additional projections were made to evaluate the range of Sea elevations that could be projected for Case A-1 under variable conditions of inflow. The process used to make these projections reflects the "cycling" of the annual historic condi- tions, adjusted as mentioned above, for each year of the 29-year period of record. The first of the 29 model runs was made starting with the historic data for 1960 as the assumed condition for 1991, a second run was made starting with historic data for 1961 as the assumed condition for 1991, and so forth, until the 29th run, which started with data for 1988 as the assumed condition for 1991, was made. The data were then wrapped around so that 1960 data were used for the assumed condition for 1992, etc. This method of analysis is commonly referred to as the index sequential method of analysis.
The results of these 29 model runs were used to depict the elevation extremes projected for the future based on the sequential cycling of historic conditions as the basis for future inflow conditions. Figure 7 presents the highest and lowest elevations encountered in the 29 model runs for each year from 1991 through 2020. The development of the highest and lowest elevations shown on Figure 7 are illustrated on Figure 8 where two of the 29 model run traces are depicted. One of these traces begins with data for 1967 as the assumed condition for 1991, and the other begins with data for 1975 as the assumed condition for 1991. Following these traces through the year 2020 illustrates how each trace determines one of the highest and lowest points shown on Figure 8. The other 27 traces (not shown) determine the remaining highest and lowest points for the balance of the years.
Figure 7 indicates that, in any given year, the elevation of the Sea could deviate from the average projection by up to four feet. As Figure 7 illustrates, the elevation of the Sea could experience a rise during the next few years even under Case A-1. Seasonal variations in the elevation of the Sea of 1 foot are commonly experienced within the same year.
Figure 9 depicts the salinity of the Sea, under average future conditions, for the current level case and the two assumed levels of additional conservation. These projections were based on future inflow patterns reflecting average conditions for the period 1960-1988 adjusted for conservation, Colorado River salinity projected at Imperial Dam and flow from Mexico. Under the current level case, the salinity is projected to rise gradually from its December 1991 value of 43,200 ppm to a concentration of about 49,300 ppm by the year 2000 and to over 60,000 ppm by the year 2020. Under Case A-1 and Case A-2, the salinity concentration is projected to increase to about 51,500 ppm and 53,700 ppm, respectively, in the year 2000. For each of the additional levels of conservation, the result would be to advance the date that a concentration of 50,000 ppm would be reached. Under Case A-1 the date would be advanced by about three years and under Case A-2 by about four years. By the year 2020, the salinity concentrations for the additional levels of conservation are projected to reach about 67,000 ppm and 79,600 ppm, for Case A-1 and Case A-2, respectively.
Figure 10 depicts projections of the range of future salinity concentrations under Case A-1. The highest and lowest salinity concentrations shown on Figure 10 were derived using the same process of sequential cycling of historic conditions for the 29-year period as was used for the Sea elevations shown on Figure 7. Figure 11 illustrates the development of the highest and lowest salinity concentrations shown on Figure 10 by using the same two example years used for Sea elevations on Figure 8.
Figure 10 indicates that the range of salinity of the Sea in any given year could deviate from the average projection by up to 8,000 ppm. This variation in salinity could occur depending on future conditions. Variations in agricultural demand for water, for example may change as much as 500,000 acre-feet over a relatively short period as experienced between 1983 and 1990. It is noteworthy to point out, as depicted on Figure 10, that even under the most favorable hydrologic conditions (an initial series of wet years), the salinity of the Sea is not expected to significantly decline below the current concentrations and most likely would continue to remain at concentrations above 40,000 ppm for Case A-1. This condition is also true for the current level case, although the results were not graphed.
Effects Related to Elevation and Salinity Changes
Changes in elevation and salinity of the Sea affect human resources as well as fish and wildlife resources. Effects on these resources resulting from changed conditions due to existing and possible future conservation measures are discussed in the following paragraphs.
The reduction in the elevation of the Sea under the first additional level of conservation (Case A-1) would amount to slightly more than one foot over the next 10 years increasing to nearly 3 feet by the year 2020. This lowering of elevation, though gradual, would expose about 3,600 acres along the shoreline in the year 2000 and about 8,400 acres by the year 2020, about 1.5 percent and 3.5 percent of the present 242,000-acre surface area, respectively. Most of the exposed shoreline would be to the north and south ends of the Sea where the elevation gradient is the smallest. Much of this land, particularly at the south end was used for agricultural purposes before being inundated. Productive use of the exposed lands through the return of agriculture or the development of wetlands, marshes and other wildlife projects would reduce any adverse effects from dust. As a major portion of the Salton Sea National Wildlife Refuge lies in the Sea, some of this land would be exposed offering opportunities for the USFWS to consider redeveloping selected areas to further enhance waterfowl habitat. The lowering of the elevation of the Sea would lower the high water table under the nearby agricultural lands south of the Sea which would reduce drain maintenance and related costs. Habitat for the desert pupfish in and around the drains would be improved by the lowering of the Sea.
Developments in Salton City and Desert Shores have included waterfront housing constructed alongside artificial channels which connect to the Sea. A drop in elevation of five feet may necessitate periodic dredging to keep the channels functional. Channel-side facilities would need some modifications over time to accommodate access to the lowered channel.
While the trend of the Sea elevations is expected to be declining under average future conditions for Case A-1, as indicated on Figure 7, there is the possibility of increases in Sea elevations within the next decade in the order of three to four feet if a continuous series of wet years is experienced during that period. Developments along the shoreline in some areas may require provisions to avoid flooding and to accommodate the higher water elevations. Commercial property along the Sea that would be directly affected by lowering elevations would consist of marinas and boat ramps and other related access facilities.
As some existing boat ramps were used prior to the increase in elevation of the Sea, they probably could be used at lower elevations. Other boat ramps developed more recently could be extended, or replaced by floating boat ramps, which have been used successfully in many locations where elevation changes are common. Floating marinas (bait shops, fuel docks, et cetera) have also been used successfully in other locations.
Land exposed by lowering elevations of the Sea would also provide space to develop additional facilities at each community. Potential uses in these areas could include picnicking and sports facilities, biking and hiking paths and boardwalks.
Facilities at the Salton Sea State Recreation Area would be affected by the elevation reductions. The existing boat ramps would probably require modifications. While camping and picnicking areas would be further away from the Sea, additional exposed shoreline would provide areas where additional facilities could be constructed.
Geothermal companies have expressed interest in additional drilling under the Sea. Exposure of additional shoreline would probably make drilling less costly and easier. Lowering of Sea elevations would also reduce the need for existing dikes and levees currently protecting agricultural land and some geothermal facilities, and would reduce the need for similar construction at future sites.
The increasing salinity that would accompany lowering of the Sea under the first additional level of conservation would only impact fish and wildlife resources to the extent that higher salinity concentrations would be reached a few years earlier. This is because salinity concentrations under the current level case are also expected to increase. Although not expected to return to salinity concentrations as low as 40,000 ppm, even under the current level case, the Sea could sustain a fishery for some time into the future if supplemented by warm water hatchery stocks from the existing Niland Warmwater Fish Hatchery and/or from newly constructed facilities.
There is much speculation as to the level of salinity at which a viable fishery will continue or when reproduction of any one species will be totally lost. It is possible that the most salt tolerant species the desert pupfish, would be able to continue reproduction in the outfalls of the New, Alamo, and Whitewater Rivers longer than they would be able in the remainder of the Sea. It seems unlikely that the species that depend upon general distribution of fertilized eggs would be able to survive under sustained increases in salinity with or without additional conservation.
Water in the Sea currently has a selenium concentration of approximately 2.5 ppb. Not enough is currently known about the mechanisms affecting selenium chemistry in the Sea area to predict what effect water conservation may have on future selenium levels in water or sediments. Included in the complexities are food chain organisms which bring selenium up from bottom sediments, and how future increases in salinity may affect their numbers and/or feeding habits.
Economically, the existing sport fishery is probably the most significant factor related to the Sea. The resident fish species are also the foundation for fish-eating wildlife and waterfowl species in the area. Other fish populations could be sustained if artificial ponds and marshes were created near the Sea. These would probably include catfish, bass, and bluegill cultures. The principal purpose of these ponds and wetlands would be to provide habitat for endangered species (Yuma clapper rail) and other resident waterfowl.
Effects Related to Reduction of Water Shortfalls and Increased Economic Stimulus
Through water conservation, additional water is made available for other uses, reducing the shortfall in water supplies projected for Southern California. In addition, economic stimulus is provided to the Imperial County economy through increased construction activity related to the conservation measures. Litigation due to high water levels of the Sea should be reduced. To date, IID and CVWD have made payments in excess of $20 million for flood damages.
PLANS TO CONTROL THE ELEVATION AND SALINITY OF THE SEA
In the early 1920`s the federal government recognized that the primary function of the Sea was to serve as a repository for agricultural drainage. It did this by withdrawing all federal land under the Sea for a public water reserve. In the 1960's both federal and state governments, in joint studies, reaffirmed this primary function of the Sea in documents aimed at controlling the elevation and salinity of the Sea, and a "Salton Sea Project" was proposed. The project was never constructed because of lack of funding.
In 1986, a Salton Sea Task Force was formed as an ad hoc group under the California Resources Agency to review proposals to stabilize the elevation and salinity of the Sea consistent with the primary function of the Sea as an agricultural drainage repository. A group of 20 interested agencies were asked to participate as members of the Task Force. Plans considered by the Task Force to manage the Sea can be divided into two groups: plans to reduce salinity, and plans to stabilize the elevation of the Sea.
Plans to reduce salinity include the use of solar pond technology which concentrates Sea water into dense brines and then pumps the solution out of the Salton Sea Basin. The Salton Sea Project proposed to control the salinity by creating basins within the Sea and concentrating Sea water in place in the bottom of the basin. Another salinity control measure that has been considered is the introduction of treated sewage effluent imported from San Diego County.
Plans to stabilize the level of the Sea include the construction of ponds on the periphery of the Sea which would increase the net water surface area exposed to evaporation. Another elevation control measure would be the construction of a Panama Canal-type waterway through the Republic of Mexico with locks and exchange water with the Gulf of California.
As all of these plans encompass substantial costs, the Task Force efforts continue in exploring various means of gaining economic justification and financial feasibility of the plans and seeking some form of regional organization as a sponsoring entity to carry out and provide funding for preservation measures for the Sea.
The Salton Sea has been designated as a repository
for agricultural drainage waters. As with any other closed basin,
evaporation will lead to the concentration of remaining salts. For
the past decade, inflow has been approximately the same as
evaporation, resulting in a Sea with a relatively stable elevation
but with increasing salinity. Additional water conservation will
reduce the elevation of the Sea and increase the rate at which
salinity concentrations are rising. Stabilizing the elevation and
salinity would require large expenditures of energy and capital. The
following summarizes the highlights of the report.