|The Coachella Valley Basin|
|Introduction||Basin and Range||Climate||Hydrological Setting||Hydrologic Properties||Geology||Water Resource||Contamination||References|
The Coachella Valley Basin is the terminal sink of the basin and range fill aquifer located within the Basin Range Physiographic Providence. Located in the northern region of the Salton Trough, in Riverside County, California it is characterized by warm summer days and mild winters with low average precipitation. The Coachella Valley aquifer is generally an unconsolidated, moderately to highly permeable aquifer. It is naturally recharged through percolation of surface water, drainage of intermittent streams, and through runoff from nearby mountain ranges. The Coachella Valley Basin is also artificially recharged from the Colorado River through man-made canals. The Coachella Valley Aquifer is the main source of potable water for the surrounding desert area and is relied upon heavily by commercial and residential properties. Geologic properties have split the aquifers into four distinct subbasins, all with distinct hydrological properties.
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Basin and range fill aquifers are found in portions of Nevada, California, Utah, Arizona, New Mexico, and southern Oregon and Idaho. There are three principal types of aquifers within the Basin and Range providence that are collectively called “Basin range fill aquifers”. Regional aquifers are not continuous within the basin and range fill region and are further broken up into four basin types based on recharge-discharge function and ability. All Basin and range fill aquifers are bounded, in some combination, by fault lines and impermeable rocks of mountain ranges (“Ground Water Atlas of the United States, California, Nevada, HA 730-B”).
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The Coachella Valley Basin is located in the Colorado Desert Region. The northern portion of this region has one rainy season, and experiences greater summer daytime temperatures than higher elevation deserts. Deserts in this region never experience frost. ("Colorado Desert - Overview").
According to data collected by the Western Regional Climate Center at the Mecca 2, SE, California Station, the annual mean temperature in the Coachella Basin is 72.5 degrees Fahrenheit with monthly average temperatures ranging form 107.3 degrees Fahrenheit in July to 69.9 degrees Fahrenheit in January. The Mecca 2, SE station recorded mean precipitation to be 2.81 inches with monthly average precipitation ranging from 0.56 inches in January to 0.01 inches in June (“Mecca 2, SE, California”).
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The Coachella Valley Basin is located within the Colorado Desert Region, characterized by low precipitation. (“The Colorado Desert -- An Overview”). Average annual rainfall over the Coachella Valley Basin is less than 3 inches on the valley floor and about 40 inches in the mountains (Ground Water Atlas of the United States, California, Nevada, HA 730-B).
Water bodies in the Coachella Valley Basin include the Salton Sea, Whitewater River, and various other small streams and creeks. The Salton Sea is the largest body of water in the Coachella Valley Basin. It was created in 1905 when the Colorado River broke through an irrigation project and settled into a depressed, saline filled lake bed. The Salton Sea is 235 feet below sea level and is 35 miles long and 15 miles wide (“The Colorado Desert -- An Overview”).
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The Coachella Valley Basin is a basin and range fill aquifer. It is generally an unconfined aquifer composed of coarse-grained sediments. Basin fill can be more than 3,000 feet thick and is moderately to highly permeable (Ground Water Atlas of the United States, California, Nevada, HA 730-B). Most basin and range fill aquifers recharge from snowmelt from local mountain ranges, however the most important source for recharge of the Coachella Valley aquifer is water from the Colorado River through man-made canals (“Ground Water Atlas of the United States, California, Nevada, HA 730-B”). These canals were first built u 1948 and can be up to 200 feet wide. Over time the unlined canals caused ground-water levels to rise to the water level in the canal. In some areas the canals caused the groundwater to rise more than 70 feet, although groundwater levels within the basin are generally declining caused by the urbanization of the area (Ground Water Atlas of the United States, California, Nevada, HA 730-B).
Geological properties have divided the basin up into four distinct subbasins: Indio, Mission Creek, Desert Hot Springs and the San Gorgonio Pass Subbasins. Each basin has slightly different hydrologic properties and is further discussed below.
The Indio subbasin is located northwest of the Salton Sea and has a surface area of 336,000 acres. It is the largest of the four subbasins and leads in groundwater storage area. It is drained by the Whitewater River and its tributaries. Surface flow is genearlly southwest toward the Salton Sea. The subbasin is recharged by surface runoff and subsurface inflow as wells as through artificial through the Coachella Canal from the Colorado River Aqueduct (“Coachella Valley Groundwater Basin, Indio Subbasin”).
Groundwater in the northern portion of the subbasin is unconfined, but becomes confined in the southern portion. Groundwater is confined from Point Happy southward to the Salton Sea. The Indio subbasin is made up of unconsolidated Pleistocene and Holocene alluvial deposits. The primary water-bearing unit is the Ocotillo Conglomerate which is greater than 1,000 feet thick in some areas (“Coachella Valley Groundwater Basin, Indio Subbasin”).
Depth to groundwater varies widely in this subbasin, with groundwater levels steadily declining throughout the subbasin. A period of rising groundwater levels occurred from 1949 through 1980s caused by artificial recharge. Since the 1980s groundwater pumping has increased and groundwater had declined despite continuing efforts through artificial recharge (“Coachella Valley Groundwater Basin, Indio Subbasin”).
Groundwater in the Indio Subbasin has a total dissolved solids (TDS) content of 300 mg/L and is mainly calcium bicarbonate in character. Groundwater near the Whitewater spreading grounds varies between sodium sulfate and calcium sulfate in character. (“Coachella Valley Groundwater Basin, Indio Subbasin”).
The Mission Creek Subbasin is located northwest of the Salton Sea and covers a surface area of 49,000 acres. This subbasin is in the northwestern part of a large structural trough that includes the Desert Hot Springs Subbasin and the Gulf of California. This subbasin underlies the northwest portion of the Coachella Valley. Major surface water features include the Whitewater River, Mission Creek, San Gorgonio River, and the Little and Big Morongo Washes (“Coachella Valley Groundwater Basin, Mission Creek Subbasin”).
Water bearing formations are relatively unconsolidated late Pleistocene, alluvial Holocene, and terrace deposits. The upper 2,000 feet of the deposits, which are as deep as 7,000 feet in some areas, are water-bearing. The upper portions of the deposits are coarse grained with high specific yields. Some yields are as high as 3,000 gallons per minute. However, despite the high permeibility of the basin material there is a relatively flat gradient indicating that the rate of movement is genearlly slow. (“Coachella Valley Groundwater Basin, Mission Creek Subbasin”).
Recharge in the subbasin occurs from intermittent creeks and rivers from surrounding highlands. Some subsurface leakage occurs from the Desert Hot Springs Subbasin across the Mission Creek Fault. The average depth to water is 372 feet, but levels in domestic wells vary from 140 to 721 feet. Water levels have been declining since to the 1950s and are attributed to groundwater extractions. Groundwater in storage is estimated to be 1,400,000 acre-feet (“Coachella Valley Groundwater Basin, Mission Creek Subbasin”).
Chemical composition of the natural groundwater in the Mission Creek Subbasin ranges from a calcium-magnesium bicarbonate type to sodium chloride-sulfate type. This subbasin has a TDS content below 500mg/l. (“Coachella Valley Groundwater Basin, Mission Creek Subbasin”)
The Desert Hot Springs Subbasin is located northwest of the Salton Sea, underlying the northeaster portion of the Coachella Valley. It has a surface area of 101,000 acres and forms the boundary from the Little Morongo Canyon southeast to Pushawalla Canyon in the Indo Hills (“Coachella Valley Groundwater Basin, Desert Hot Springs Subbasin”).
The Desert Hot Springs Subbasin is composed of unconsolidated late Pleistocene and Holocene alluvial deposits. Groundwater is unconfined, with water bearing deposits estimated to be greater than 700 feet (“Coachella Valley Groundwater Basin, Desert Hot Springs Subbasin”).
Recharge occurs from seasonal runoff draining form the Little San Bernardino Mountains through intermittent creeks and percolation through the alluvial fan deposits. Water level data is sparse in most of the subbasin, but has been documented to range from 12 feet below ground surface to over 300 feet below groundwater. Groundwater flow is generally southeastward toward the Mecca Hills-Thermal Canyon area. Groundwater storage and was estimated to be 172,000 acre-feet in 1961, but is to have declined slightly. (“Coachella Valley Groundwater Basin, Desert Hot Springs Subbasin”).
The 1968 to 1974 chemical analysis of the groundwater indicated that sodium sulfate type groundwater exists throughout the Desert Hot Springs Subbasin. The analysis also indicated higher than average levels of TDS values ranged from 800 to 1000mg/l, and chloride levels of 1000 to 150 mg/l were also noted.
The San Gorgonio Pass Subbasin lies entirely within the San Gorgonio Pass area. Major water bearing deposits are of Holocene and Pleistocene age alluvium as well as Pliocene to Pleistocene aged San Timoteo Formation. The Holocene alluvium is composed mostly of gravel and sand, but lies above the water table contributing little water to wells. The Pleistocene age alluvium is comprised of sand, gravel, clay and silt and yields moderate amounts of water to wells. The San Timoteo Formation is one of the major water bearing deposits in the subbasin. It may extend over 2,000 feet below the surface and consists of poorly sorted to sorted, partly consolidated, fine to courses sandstone with layers of gravel and clay. Yields are typically poor, but some deep wells yield more than 1,000 gallons per minute (“Coachella Valley Groundwater Basin, san Gorgonio PassSubbasin”).
Groundwater gradients are steep throughout most of the subbasin caused by the development of the San Jacinto Tunnel. The construction of the tunnel caused groundwater levels to decline significantly as groundwater was pumped and diverted in to the Indio Subbasin. Groundwater storage for the entire basin was estimates at 1,400,000 acre-feet (“Coachella Valley Groundwater Basin, san Gorgonio PassSubbasin”).
The San Gorgonio Pass Subbasin is characterized by calcium-sodium bicarbonate type groundwater with TDS ranging from 106 to 205mg/l. (“Coachella Valley Groundwater Basin, San Gorgonio Pass Subbasin”).
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Six million years ago spreading of the Pacific and North American Plates caused the lithosphere near the Coachella Valley to subside creating the Salton Trough. As the trough opened it was filled with sediment from the Colorado River delta. The Coachella Valley is the northernmost portion of the Salton Trough and in some areas is filled with 3,700 meters of sediment. The upper 610 meters of sediment make up the aquifer system (Sneed and Brandt).
The aquifer system consists of unconsolidated to partly consolidated alluvial and lacustrine gravel, sand, silt, and clay. Grain sizes differ based on distance from mountain runoff and from lacustrine deposition from ancient Lake Cahuilla. The grain sizes range from fine grained in the southern portion to coarse grained in the northern portion (Sneed and Brandt).
Geologic structures in the Coachella Valley influence groundwater flow in the basin. The Coachella Valley basin is bounded by the Little San Bernardino Mountains on the north and east and by the San Jacinto and the Santa Rosa Mountains on the southwest. Portions of the San Andreas Fault system including the mission Creek, banning, Garnet Hill, and Indio Hills Faults act as barriers to groundwater flow. The faults have split the aquifer into four subbasins: Indio, Mission Creek, Desert Hot Springs, and San Gorgonio Pass subbasins (Ground Water Atlas of the United States, California, Nevada, HA 730-B).
Various studies have indicated that the Coachella Valley is subsiding, but the rate of subsidence varies. The subsidence has been attributed to the combination of the geological properties of the basin and the stress placed on aquifers caused by excessive groundwater pumping. A recent study indicated that at eight of fourteen monitoring sites subsidence rates increased by a factor of ten between 2000 and 2005. Other monitoring sites indicated that in three areas of the Coachella Valley the subsidence rates range from three to more than six millimeters per month. Other study areas indicate that subsidence is not occurring as rapidly, only subsiding an average of 150 millimeters from 1930 to 1996 (Sneed and Brandt).
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The Coachella Valley Basin provides water to major water districts in the Palm Springs and Coachella area. This area has experienced major declines in water levels in the recent years due to the growing population of the Palm Springs and surrounding areas(Ground Water Atlas of the United States, California, Nevada, HA 730-B). Water withdrawals increased more than tenfold during 1938 to 1967. The declining water levels prompted the development of the Coachella Canal which was completed in 1948.
The main water district in the area is the Coachella Valley Water District. The CVWD derives all of its drinking and domestic water from the Coachella Valley Water Basin. They sell 125,000 acre -foot of water each year. Additionally, each year 330,000 acre-feet of water is diverted from the Colorado River Water through the Coachella Canal. One-half to two-thirds of water used for irrigation comes primarily from this canal. The remaining one-half to one-third of irrigation is obtained from the local groundwater through privately owned wells. There are many golf courses in this area that require a large supply of water to maintain their facilities. Many golf courses in the area use local groundwater to water their facilities, however many are switching to reclaimed water (“Where the Water Comes From”).
Desert Water Agency reported that in 1990 its consumption reached 45,000 acre-feet (“Water Info”).
The Mission Springs Water District obtains its water the majority of its water from the Mission Creek Subbasin. Mission Springs Water district supplied approximately 30,000 people pumping 10,867 acre-feet in 2007 ("About MSWD").
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The state water resources board is responsible for the preservation, enhancement, and restoration of the quality of California’s Water. The state is broken up into twelve regions for more efficient monitoring and regulation. The Coachella Valley Basin is located in Region 7, the Colorado River Basin. The regional water boards maintain records of violations, contamination and remediation efforts. ("Water Board")
Underground storage tanks (USTs) are a common source of groundwater contamination. There are currently 110 active cases open within Region 7 of the RWQCN for the Colorado River Basin. The status of these sites range from site assessment, to remediation, case open, and monitoring. ("GeoTracker")
Other sources of contamination are located on the Environmental Protection Agency website. Superfund sites are sites that considered uncontrolled hazardous wastes sites. The most dangerous of these sites are put on the national priority list (NPL). There are two superfund sites located within Riverside County, but are located northwest of the Coachella Valley Basin. ("Cleanup")
The Department of Toxic Substance Control is the state regulatory agency on hazardous waste, contamination cleanup, and contamination prevention. The Envirostar program allows users to view areas of contamination on an interactive map. According to the Envirostor map there is one site currently “State Response” within the Coachella Valley. The site was listed in 1982 as a possible contaminant for groundwater not used for drinking water. It is still being monitored for the following contaminants: pesticides, ammonia, and volatile organics. ("Find Cleanup Sites and Permited Hazardous Waste Facilities")
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"About MSWD." Mission Springs Water District. http://www.mswd.org/operations/about/company.htm
"Cleanup." Environmental Protection Agency. United States Environmental Protection Agency. http://www.epa.gov/ebtpages/cleanup.html
"Coachella Valley Groundwater Basin, Indio Subbasin." California’s Groundwater Bulletin 118. 27 Feb 2004. http://www.dpla2.water.ca.gov/publications/groundwater/bulletin118/basins/pdfs_desc/7-21.01.pdf.
"Coachella Valley Groundwater Basin, Desert Hot Springs Subbasin." California’s Groundwater Bulletin 118. 27 Feb 2004. http://www.dpla2.water.ca.gov/publications/groundwater/bulletin118/basins/pdfs_desc/7-21.02.pdf .
"Coachella Valley Groundwater Basin, San Gorgonio Pass Subbasin." California’s Groundwater Bulletin 118. 27 Feb 2004. http://www.dpla2.water.ca.gov/publications/groundwater/bulletin118/basins/pdfs_desc/7-21.04.pdf .
"Colorado Desert - Overview." Resource Management Programs. California Department of Fish and Game. http://www.dfg.ca.gov/wildlife/WAP/region-colorado.html
"GeoTracker." State Water Research Control Board. California Environmental Protection Agency. https://geotracker.swrcb.ca.gov
"Ground Water Atlas of the United States, California, Nevada, HA 730-B ." Basin and Range Aquifers. 1995. United States Geological Survey. 25 April 2008 http://capp.water.usgs.gov/gwa/gwa.html
"Historical Climate Information." Mecca 2, SE, California. 17 Sept 2007. Western Regional Climate Center. 3 May 2008 http://www.wrcc.dri.edu/index.html
Sneed, Michelle and Justin T. Brandt. "Detection and Measurement of Land Subsidence Using Global Positioning System Surveying and Interferometric Synthetic Aperture Radar, Coachella Valley, California, 1996–2005." Scientific Investigations Report 2007–5251, United States Geological Survey 2007 1-41. 3 May 2008
"The Colorado Desert -- An Overview ." Colorado Desert Bioregion. California Environmental Resource Evaluation System. http://ceres.ca.gov/geo_area/bioregions/Colorado_Desert/about.html
"Water Board." State Department of Water Resources Board. California Environmental Protection Agency. http:// www.swrcb.ca.gov
"Water Info." Desert Water Agency. http://www.dwa.org/water_info/index.aspx
"Where The Water Comes From." Water and the Coachella Valley. Coachella Valley Water District. http://www.cvwd.org/about/waterandcv.php#where
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