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Las Vegas is the fastest growing metropolitan area in the U.S.

Las Vegas Subsidence. Las Vegas is the fastest growing metropolitan area in the U.S. It encompasses 1.2 million (2/3 of Nevada’s population) Visited by 30 million tourists each year. Subsidence.

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Las Vegas is the fastest growing metropolitan area in the U.S.

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  1. Las Vegas Subsidence • Las Vegas is the fastest growing metropolitan area in the U.S. • It encompasses 1.2 million (2/3 of Nevada’s population) • Visited by 30 million tourists each year

  2. Subsidence • Sudden sinking or gradual settling of the Earth’s surface due to the movement of subsurface earth material • Causes: • Aquifer-system compaction • Underground mining • Thawing permafrost • Drainage of organic soils • Natural compaction

  3. Las Vegas valley: -fault-bounded, hydrologic basin -highly compressible, fine-grained sediment Geology

  4. Precipitation • 1,564 square mile watershed • 24 inches precipitation occur in Spring mountains to the west • Valley receives 4 inches a year • Measurable precipitation occurs 30 days out of the year

  5. The increase in population has caused an equal increase in the demand for water • Groundwater makes up about 20% of water supply (~ 375,000 acre-feet/year) • Since 1946 withdrawal > recharge • Since 1968 efforts have been made to reduce withdrawal • Water table has decreased by 90 m in some areas

  6. Since 1935, Las Vegas has subsided by six feet • Forms fissures • Reactivates faults • Damages: • Cracks in curbs, roads, sidewalks, swimming pools, sewage lines, well failures, ruptured gas and water lines, warped railroad tracks and cracked drainage canals • Damages to homes in one subdivision are projected to be $14 million

  7. Other Concerns… • Can create new flood-prone areas by altering natural water drainage patterns • Fissures can connect contaminated surface water with aquifers • Replacement costs of collapsed wells

  8. InSAR • Interferometric Synthetic Aperture Radar • Remote sensing technique using radar satellite images • Constantly shoots radar beams at Earth’s surface and record them as they bounce back • Intensity: how much of the radar wave comes back • Phase: time it took the wave to get there and bounce back

  9. Artificial Recharge • Began in 1988 • Pump excess imported water from Lake Mead into principle aquifers • Occurs during winter months • Temporarily raises groundwater levels to postpone subsidence • Can contaminate aquifers • Disinfecting byproducts (DBPs) specifically trihalomethanes (THMs) • Despite recharge efforts, annual extraction still exceeds annual recharge

  10. Possible alternatives • Reduce groundwater withdrawal to level of net annual recharge • Designate “high-hazard” or “no build zones” • Strict regulations in already developed areas built in these hazard zones • Las Vegas Subsidence District • Long-term monitoring • More research

  11. Sources • http://pubs.usgs.gov/circ/circ1182/pdf/08LasVegas.pdf • http://www.npagroup.com/insar/apps/pdf/lasvegas_insar.pdf • http://water.usgs.gov/ogw/pubs/fs00165/ • http://geochange.er.usgs.gov/sw/impacts/hydrology/vegas_gw/ • http://www.nbmg.unr.edu/dox/nl/nl16a.htm • http://www.reviewjournal.com/lvrj_home/2006/May-21-Sun-2006/photos/3apocalypse.gif • http://quake.usgs.gov/research/deformation/modeling/InSAR/whatisInSAR.html

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