Subsidence issue causes big concern

06 January 2008 | 04:45 Code : 16449 Geoscience events
Land is sinking in parts of the Coachella Valley where groundwater is being....

  Land is sinking in parts of the Coachella Valley where groundwater is being pumped out faster than it's being replaced. If the excessive draw-down continues, infrastructure - including sewers, pipes and roads - could suffer significant damage, potentially costing taxpayers millions of dollars.That's according to a recently released study by the Coachella Valley Water District and the U.S. Geological Survey.Although Indio, the valley's largest city, is being spared the brunt of this subsidence, it's surrounded by areas in Bermuda Dunes, La Quinta and Coachella that have dropped by as much as a foot in some places.The water district provides drinking water to some Indio residences and delivers irrigation water to golf courses within the city.Most of Indio, however, is serviced by the Indio Water Authority. The authority commissioned its own survey, with the results due on Jan. 14, said Jim Smith, Indio's public works director.Water district and geological survey's report released Dec. 17 studied a period between 1996 and 2005, and showed significant changes, or sinking of the land, in at least four areas: Indian Wells, La Quinta, Palm Desert and the Coachella-Indio area."We have a problem," said Steve Robbins, the district's general manager-chief engineer. "It is a valley-wide problem we all have to deal with."The greatest drop - more than 13 inches - was measured near Bermuda Dunes Airport.The airport is in an unincorporated area between Indio and Palm Desert.Other significant areas that have dropped include:Jackson Street and 54th Avenue, Coachella - 12.28 inches.Rancho Las Palmas Golf Course, Rancho Mirage - 12.96 inches.Lake Cahuilla, La Quinta - 11.30 inches.Highway 86 and 62nd Avenue - 10.20 inches.El Dorado Drive and Osage Trail, Indian Wells - 7.99 inches.Highway 111 and 6th Street, Coachella - 7.20 inches.The report confirms the water district's concerns that the land is sinking in areas of substantial groundwater use across the Coachella Valley, Robbins said."This study tells us our assumptions are correct and underscores the importance of eliminating overdraft of the aquifer," Robbins said.An aquifer is an underground layer of rock, sediment or soil that is saturated with water.About 100,000 to 150,000 more acre-feet per year is being drained from the aquifer than is being replacing. One acre foot provides enough water for about one household a year, district spokeswoman Heather Engel said.Since the 1920s, groundwater has been important to the agricultural, municipal and domestic water supply in the valley, resulting in significant groundwater pumping that has contributed to water-level declines as much as 100 feet, according to information provided by the water district and geological survey."We've gone for many years without seeing any signs of subsidence," Robbins said.But that's all changed. Valley population growth and the building boom have put more stress on the valley's water resources, he said.Developers can no longer rely on historic water levels when planning new housing developments. Those numbers will have to be re-evaluated, he said.The underground aquifer provides the valley's only source of drinking water. The fact that it's also being used to water golf courses and for other irrigation purposes contributes to the overdraft.Smith said he will evaluate the district's report and assess its recommendations."Indio has not experienced subsidence problems and we do intend to work with CVWD and other water agencies on an integrated basis," Smith said.

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