Scientific Investigations Report 2007–5251
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5251
Version 2.0, June 2013
Ground water has been a major source of agricultural, municipal, and domestic water supply in Coachella Valley, California (fig. 1), since the early 1920s. Pumping of ground water resulted in water-level declines as large as 15 m (50 ft) between the early 1920s and late 1940s. In 1949, the importation of Colorado River water through the Coachella Branch of the All-American Canal to the southern Coachella Valley began. As a result of the importation of surface water, pumping of ground water decreased in the southern Coachella Valley during the 1950s through the 1970s, and water levels in some wells in the lower valley recovered as much as 15 m (50 ft). Since the late 1970s, however, the demand for water in the southern Coachella Valley has exceeded the deliveries of imported surface water, pumping has increased, and water levels have again declined. By 2005, water levels in many wells in the southern Coachella Valley had declined 15 to 30 m (50 to 100 ft) and water levels in some wells were at their lowest recorded levels.
Declining water levels can contribute to, or induce, land subsidence in aquifer systems that consist of a significant fraction of unconsolidated fine-grained sediments (silts and clays). Ikehara and others (1997) reported that as much as 150 mm ± 90 mm (0.5 ft ± 0.3 ft) of subsidence occurred in the southern parts of the Coachella Valley between 1930 and 1996. Land subsidence can disrupt surface drainage; cause earth fissures; and damage wells, buildings, roads, and utility infrastructure. A large earth fissure was discovered in 1948 about 3 km (2 mi) north of Lake Cahuilla in La Quinta. Because subsidence had not been documented in the southern parts of the Coachella Valley prior to the report by Ikehara and others (1997), it is not known if this fissure formed in response to differential land subsidence during the earlier period (early 1920s–late 1940s) of ground-water-level declines. However, fissuring is recurring in this area (Clay Stevens, TerraPacific Consultants, Inc., written commun., 2006). Subsidence-related earth fissures and reactivated surface faults have been identified in many other ground-water basins in the western United States (Holzer, 1984).
The Coachella Valley Water District (CVWD) works cooperatively with local stakeholders to manage the water supply for a large part of the Coachella Valley (fig. 1). Because of the potential for ground-water pumping to cause land subsidence, the CVWD entered into a cooperative agreement with the U.S. Geological Survey (USGS) to monitor vertical changes in land surface to determine if land subsidence was occurring in the Coachella Valley. In 1996, the USGS, in cooperation with CVWD, established a geodetic network of monuments to monitor vertical changes in land surface in the southern Coachella Valley using Global Positioning System (GPS) surveys and to establish baseline values for comparisons with results of future surveys. The geodetic network needs to be surveyed intermittently to determine the distribution and amount of land subsidence. In addition, interferometric synthetic aperture radar (InSAR) data collected since 1996 have been used to detect and quantify land subsidence in areas removed from the geodetic monuments.
The objectives of this study are to detect and quantify land subsidence that has occurred in the Coachella Valley from 1996 through 2005 by completing GPS surveys at the established geodetic network of monuments and by using InSAR data. This report presents the results and interpretations of GPS data collected at the monuments in the monitoring network during surveys in 1996, 1998, 2000, and 2005, and also of spatially detailed maps of vertical land-surface changes generated using InSAR data collected between 1996 and 2005. The InSAR-generated maps extend from near Palm Springs to near the Salton Sea (fig. 1). Data showing ground-water-level change during 1996–2005 were examined and compared with the GPS measurements and the InSAR-generated maps to determine if the vertical changes in land surface may be related to the changes in ground-water levels.
The Coachella Valley is a 100-km (65 mi) long, northwest-trending valley in southeastern California (fig. 1). The valley covers about 1,000 km2 (400 mi2) (California Department of Water Resources, 1964) and includes the cities of Cathedral City, Coachella, Desert Hot Springs, Indio, La Quinta, Palm Desert, Palm Springs, and Rancho Mirage. The valley is bordered by the San Jacinto and Santa Rosa Mountains on the west, the San Bernardino and the Little San Bernardino Mountains on the north, the Cottonwood Mountains and the Mecca Hills on the east, and the Salton Sea on the south (fig. 1). The Coachella Valley is drained primarily by the Whitewater River, which flows into the Whitewater Stormwater Channel and eventually discharges into the Salton Sea (fig. 1). Land-surface elevations vary from more than 70 m (230 ft) below sea level at the Salton Sea to more than 3,000 m (10,000 ft) above sea level at the peaks of the surrounding mountains.
The climate of the Coachella Valley floor is arid. Average annual rainfall ranges from 80 mm (3 in) on the valley floor to more than 760 mm (30 in) on the crests of the mountains to the west and north of the valley (California Department of Water Resources, 1964). Temperatures range from about 50ºC (120ºF) on the valley floor in the summer to below 0ºC (32ºF) in the surrounding mountains in the winter.
This study is the fourth in a series of Coachella Valley land-subsidence studies that have been completed by the USGS in cooperation with CVWD. Ikehara and others (1997) documented the development of the geodetic monitoring network and areas of possible land subsidence in Coachella Valley by comparing historical leveling measurements with GPS surveying measurements made in 1996. The vertical changes in land surface between 1996 and the earliest measurements at monuments in the monitoring network do not exceed 150 mm (0.5 ft) (Ikehara and others, 1997). The range of uncertainty (±90 mm or ±0.3 ft) of these calculated vertical changes in land surface, however, is large because the historical leveling surveys were done at different times and sometimes by different agencies using different methods. Furthermore, the methods used for the leveling surveys had different standards of accuracy and the networks were of different geographic extents (Ikehara and others, 1997). Sneed and others (2001) reported that GPS measurements indicated small amounts of subsidence between 1996 and 1998 at some monuments in the monitoring network; Sneed and others (2002) reported that GPS measurements indicated most monuments were fairly stable between 1998 and 2000. Sneed and others (2001, 2002) also used InSAR to detect and quantify land subsidence throughout much of the Coachella Valley. InSAR measurements made between 1996 and 2000 indicated that as much as 150 mm (0.49 ft) of land subsidence occurred in areas near Palm Desert, Indian Wells, and La Quinta (Sneed, 2001, 2002).
U.S. Department of the Interior | U.S. Geological Survey
URL: https://pubs.usgs.gov/sir/2007/5251
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