The lake occupies the lowest elevations of the Salton Sink in the Colorado Desert of Imperial and Riverside Counties in Southern California. Its surface is 236.0 ft (71.9 m) below sea level as of January 2018. The deepest point of the sea is 5 ft (1.5 m) higher than the lowest point of Death Valley. The sea is fed by the New, Whitewater, and Alamo rivers, as well as agricultural runoff, drainage systems, and creeks.
Over millions of years, the Colorado River has flowed into the Imperial Valley and deposited soil (creating fertile farmland), building up the terrain and constantly changing the course of the river. For thousands of years, the river has flowed into and out of the valley alternately, creating a freshwater lake, an increasingly saline lake, and a dry desert basin, depending on river flows and the balance between inflow and evaporative loss. The cycle of filling has been about every 400–500 years and has repeated itself many times. The latest natural cycle occurred around 1600–1700 as remembered by Native Americans who talked with the first European settlers. Fish traps still exist at many locations, and the Native Americans evidently moved the traps depending upon the cycle.
The most recent inflow of water from the now heavily controlled Colorado River was accidentally created by the engineers of the California Development Company in 1905. In an effort to increase water flow into the area for farming, irrigation canals were dug from the Colorado River into the valley. The canals suffered silt buildup, so a cut was made in the bank of the Colorado River to further increase the water flow. The resulting outflow overwhelmed the engineered canal, and the river flowed into the Salton Basin for two years, filling the historic dry lake bed and creating the modern sea, before repairs were completed.
While it varies in dimensions and area with fluctuations in agricultural runoff and rainfall, the Salton Sea is about 15 miles (24 km) by 35 miles (56 km). With an estimated surface area of 343 square miles (890 km2) or 350 square miles (910 km2), the Salton Sea is the largest lake in California. The average annual inflow is less than 1,200,000 acre feet (1.5 km3), which is enough to maintain a maximum depth of 43 feet (13 m) and a total volume of about 6,000,000 acre feet (7.4 km3). However, due to changes in water apportionments agreed upon for the Colorado River under the Quantification Settlement Agreement of 2003, the overall water level of the sea is expected to decrease significantly between 2013 and 2021.
The lake's salinity, about 56 grams per litre (9.0 oz/imp gal), is greater than that of the waters of the Pacific Ocean (35 g/l (5.6 oz/imp gal)), but less than that of the Great Salt Lake (which ranges from 50 to 270 g/l (8.0 to 43.3 oz/imp gal)). Recently, the concentration has been increasing at a rate of about 3% per year. About 4,000,000 short tons (3.6×109 kg) of salt are deposited in the valley each year.
The area was once part of a vast inland sea that covered a large area of Southern California. Geologists estimate that for three million years, at least through all the years of the Pleistocene glacial age, a large delta was deposited by the Colorado River in the southern region of the Imperial Valley. Eventually, the delta reached the western shore of the Gulf of California, creating a barrier that separated the area of the Salton Sea from the northern reaches of the Gulf. Were it not for this barrier the entire Salton Sink along with the Imperial Valley would be submerged as the Gulf would extend as far north as Indio.
Since the exclusion of the ocean, the Salton Basin has over the ages been alternately a freshwater lake, an increasingly saline endorheic lake, and a dry desert basin, depending on river flows and the balance between inflow and evaporative loss. A lake exists only during times it is replenished by the rivers and rainfall, a cycle that has repeated itself many times over hundreds of thousands of years, perhaps cycling every 400 to 500 years.
Evidence that the basin was occupied periodically by multiple lakes includes wave-cut shorelines at various elevations preserved on the hillsides of the east and west margins of the present lake, the Salton Sea. These indicate that the basin was occupied intermittently as recently as a few hundred years ago. The last of the Pleistocene lakes to occupy the basin was Lake Cahuilla, also periodically identified on older maps as Lake LeConte or the Blake Sea, after American professor and geologist William Phipps Blake.
Throughout the Spanish period of California's history, the area was referred to as the "Colorado Desert" after the Colorado River. In a railroad survey completed in 1855, it was called "the Valley of the Ancient Lake". On several old maps from the Library of Congress, it has been found labeled "Cahuilla Valley" (after the local Native American tribe) and "Cabazon Valley" (after a local Native American chief – Chief Cabazon). "Salt Creek" first appeared on a map in 1867 and "Salton Station" is on a railroad map from 1900, although this place had been there as a rail stop since the late 1870s. Until the advent of the modern sea, the Salton Sink was the site of a major salt-mining operation.
In 1900, the California Development Company began construction of irrigation canals to divert water from the Colorado River into the Salton Sink, a dry lake bed. After construction of these irrigation canals, the Salton Sink became fertile for a time, allowing farmers to plant crops.
Within two years, the Imperial Canal became filled with silt from the Colorado River. Engineers tried to alleviate the blockages to no avail. In 1905, heavy rainfall and snowmelt caused the Colorado River to swell, overrunning a set of headgates for the Alamo Canal. The resulting flood poured down the canal, breached an Imperial Valley dike, and ran down two former dry arroyos: the New River in the west, and the Alamo River in the east, each about 60 mi (97 km) long. Over about two years, these two newly created rivers sporadically carried the entire volume of the Colorado River into the Salton Sink.
The Southern Pacific Railroad tried to stop the flooding by dumping earth into the canal's headgates area, but the effort was not fast enough, and the river eroded deeper and deeper into the dry desert sand of the Imperial Valley. A large waterfall formed as a result and began cutting rapidly upstream along the path of the Alamo Canal that now was occupied by the Colorado. This waterfall was initially 15 feet (4.6 m) high, but grew to 80 feet (24 m) high before the flow through the breach was stopped. Originally, it was feared that the waterfall would recede upstream to the true main path of the Colorado, becoming up to 100 to 300 feet (30 to 91 m) high, at which point it would be practically impossible to fix the problem.
As the basin filled, the town of Salton, a Southern Pacific Railroad siding, and Torres-Martinez Native American land were submerged. The sudden influx of water and the lack of any drainage from the basin resulted in the formation of the Salton Sea.
The U.S. Navy conducted a preliminary inspection of the Salton Sea in January 1940, and the Salton Sea Test Base (SSTB, run by Sandia Labs) was initially commissioned as the Naval Auxiliary Air Station, Salton Sea, in October 1942. The SSTB, just to the south-east of Salton City, originally functioned as an operational and training base for seaplanes. Additional activities at the base have included experimental testing of solidfuel plane-launched rockets, jet-assist take-off testing, aeroballistic testing of inert atomic weapon test units at land and marine target areas, training bombing at marine targets, testing of the effects of long-term storage on atomic weapons, testing of the parachute landing systems of the Project Mercury space capsules, parachute training and testing, and military training exercises. The base was abandoned in 1978.
The continuing intermittent flooding of the Imperial Valley from the Colorado River led to the idea of the need for a dam on the Colorado River for flood control.
The Salton Sea had some success as a resort area, with Salton City, Salton Sea Beach, and Desert Shores, on the western shore and Desert Beach, North Shore, and Bombay Beach, built on the eastern shore in the 1950s. However, many of the settlements substantially shrank in size, or have been abandoned, mostly due to the increasing salinity and pollution of the lake over the years from agricultural runoff and other sources. Many of the species of fish that lived in the sea have been killed off by the combination of pollutants, salt levels, and algal blooms. Dead fish have been known to wash up in mass quantities on the beaches. The smell of the lake, combined with the stench of the decaying fish, also contributed to the decline of the tourist industry around the Salton Sea. Many people now visit the Salton Sea and the surrounding settlements to explore the abandoned structures. The town of Niland is 1.5 miles (3 km) southeast of the sea, with a population of 1,006. Evidence of geothermal activity is also visible. Mudpots and mud volcanoes are found on the eastern side of the Salton Sea. A number of geothermal electricity generation plants are located along the southeastern shore of the Salton Sea in Imperial County.
The US Geological Survey describes the smell as "objectionable", "noxious", "unique", and "pervasive".
Due to the high salinity, very few fish species can tolerate living in the Salton Sea. Introduced tilapia are the main fish that can tolerate the high salinity levels and pollution. Other freshwater fish species live in the rivers and canals that feed the Salton Sea, including threadfin shad, carp, red shiner, channel catfish, white catfish, largemouth bass, mosquitofish, sailfin molly, and the vulnerable desert pupfish.
The Salton Sea has been termed a "crown jewel of avian biodiversity" by Dr. Milt Friend of the Salton Sea Science Office. Over 400 species have been documented at the Salton Sea. The most diverse and probably the most significant populations of bird life in the continental United States are hosted, rivaled only by Big Bend National Park in Texas. It supports 30% of the remaining population of the American white pelican. The Salton Sea is also a major resting stop on the Pacific Flyway. On 18 November 2006, a Ross's gull, a high Arctic bird, was sighted and photographed there.
The lack of an outflow means the Salton Sea does not have a natural stabilization system; it is very dynamic. Fluctuations in the water level caused by variations in agricultural runoff, the ancient salt deposits in the lake bed, and the relatively high salinity of the inflow feeding the sea are all causing ever-increasing salinity. The body was initially a freshwater lake, but by the 1960s its rising salinity had begun to jeopardize some of the species in it. With a salinity now exceeding 5.0% w/v (saltier than seawater), most species of fish can no longer survive there. A freshwater fish notable for its ability to withstand the rising salinity of the Salton Sea, the desert pupfish, can survive salinities ranging from 0.0% to 7.0%. Fertilizer runoffs have resulted in eutrophication, with large algal blooms and elevated bacterial levels.
By 2014, large swaths of lake bed were exposed and salt levels drastically increased due to mandated water transfers to metropolitan areas along the coast and other factors, limiting the water inflow. Besides the resulting fish kills, the shrinking lake interrupts the bird migration, causes dust clouds, and impacts local tourism negatively.
Alternatives for "saving" the Salton Sea have been evaluated since 1955.
Much of the current interest in the sea was sparked in the 1990s by Congressman Sonny Bono. His widow, Mary Bono Mack, elected to fill his seat, has continued to be interested in the Salton Sea, as has Representative Jerry Lewis of Redlands. In 1998, the Sonny Bono Salton Sea Restoration Project was named for the politician.
In the late 1990s, the Salton Sea Authority, a local joint powers agency, and the US Bureau of Reclamation began efforts to evaluate and develop an alternative to save the Salton Sea. A draft Environmental Impact Report/Environmental Impact Statement, which did not specify a preferred alternative, was released for public review in 2000. Since that time, the Salton Sea Authority has developed a preferred concept[full citation needed] that involves the construction of a large dam that would impound water to create a marine sea in the northern and southern parts of the sea and along the western edge.
Many other concepts have been proposed, including piping water from the sea to a wetland in Mexico, Laguna Salada, as a means of salt export, and one by Aqua Genesis Ltd to bring in seawater from the Gulf of California, desalinate it at the sea using available geothermal heat, and sell the water to pay for the plan. This concept would involve the construction of over 20 miles (30 km) of pipes and tunneling, and, with the increasing demand for water at the coastline, would provide an additional 1,000,000 acre feet (1.2 km3) of water to Southern California coastal cities each year.
In 2003, the Imperial Irrigation District agreed to sell a portion of its allotment from the Colorado River for 45 years to the San Diego County Water Authority. The California State Legislature, by legislation enacted in 2003 and 2004, directed the Secretary of the California Resources Agency to prepare a restoration plan for the Salton Sea ecosystem, and an accompanying Environmental Impact Report. As part of this effort, the Secretary for Resources has established an advisory committee to provide recommendations to assist in the preparation of the Ecosystem Restoration Plan, including consultation throughout all stages of the alternative selection. The California Department of Water Resources and California Department of Fish and Game are leading the effort to develop a preferred alternative for the restoration of the Salton Sea ecosystem and the protection of wildlife dependent on that ecosystem.
On January 24, 2008, the California Legislative Analyst's Office released a report titled "Restoring the Salton Sea." The preferred alternative outlined in the draft plan calls for spending almost $9 billion over 25 years and proposes a smaller but more manageable Salton Sea. The amount of water available for use by humans and wildlife would be reduced by 60% from 365 mi2 (945 km2) to about 147 mi2 (381 km2). About 52 mi (84 km) of barrier and perimeter dikes – constructed most likely out of boulders, gravel, and stone columns – would be erected, along with earthen berms to corral the water into a horseshoe shape along the northern shoreline of the sea from San Felipe Creek on the west shore to Bombay Beach on the east shore. The central portion of the sea would be allowed to evaporate almost completely and would serve as a brine sink, while the southern portion of the sea would be constructed into a saline habitat complex. Construction on the project would be completed by 2035.
The sale of the Imperial water to San Diego County resulted in a reduction in agricultural runoff needed to replenish the sea. During the first 15 years, the irrigation district has been required to put water into the Salton Sea to compensate for the loss of runoff. Since the requirement expires in 2017, the district sent a letter to the California State Water Resources Control Board in 2014 asking that the board sponsor negotiations to get the state to fulfill its obligation to stop the deterioration of the sea. Pacific Institute, an Oakland-based environmental think tank, was warning that the lack of replenishment water was leading to a "period of very rapid deterioration." The rapidly shrinking sea was a "looming environmental and public health crisis" With the increased shrinkage, dust storms would increase and a rotten-egg smell could reach to the coastal cities.
The Salton Sea and surrounding basin sits over the San Andreas Fault, San Jacinto Fault, Imperial Fault Zone, and a "stepover fault" shear zone system. Geologists have determined that previous flooding episodes from the Colorado River have been linked to earthquakes along the San Andreas Fault. Sonar and other instruments were used to map the Salton Sea's underwater faults during the study. During the period when the basin was filled by Lake Cahuilla, a much larger inland sea, earthquakes higher than magnitude 7 occurred roughly every 180 years, the last one occurring within decades of 1700. Computer models suggest the normal faults in the area are most vulnerable to deviatoric stress loading by filling in of water. Currently, a risk still exists for an earthquake of magnitude 7 to 8. Simulations also showed, in the Los Angeles area, shaking and thus damage would be more severe for a San Andreas earthquake that propagated along the fault from the south, rather than from the north. Such an earthquake also raises the risk for soil liquefaction in the Imperial Valley region.
The effective drainage divide that separates the Salton Sea from the Gulf of California is about 9 m (30 ft) in elevation and is located near Delta, northeastern Baja California State, Mexico, south-southeast of Mexicali. Past sea level rise may partially be responsible for the salinity of the lake, while potential future changes in sea levels could occur. However, other factors such as hydrothermal vents, diffusion of salt from minerals and sediment, including concentrated brine, and evaporites are another contributor to salinity, as is the recent lowering of lake levels raising the salinity, though sedimentary records show the lake surface elevation reached levels 10–12 m above world sea level in the 1500s.
The temperature of the surface water changes with the seasonally varying air temperature. Winter lows can reach temperatures as low as 50 °F (10 °C) and summer highs can reach 95 °F (35 °C).
The salinity of the Pacific Ocean is approximately 35,000 mg/l (1 ppm=1 mg/l). Colorado River water salinity is about 650–700 mg/L. Salton Sea salinity is about 44,000 mg/L, that is approximately 4.4% salt. The amount of salts that is deposited in the Imperial Valley agricultural land with irrigation water is approximately four million tons of salts annually.
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