Perils of Progress - Hydrogeological Hazards in Las Vegas Valley, Clark County, Nevada

Abstract

The prehistoric Indian population in Las Vegas Valley found abundant water for their needs from springs flowing from the base of numerous fault scarps throughout the valley. The faults are generally considered to be compaction faults caused in part by subsidence resulting from dewatering aquifers as the climate became dry and warm during the interglacial periods of the Pleistocene. The valley's aquifers, for historical purposes, eventually reached steady state conditions which lasted through nearly the first half of this century. Urban growth then created a demand for water that was satisfied by overdrafting the ground-water system, which reactivated subsidence. Today, subsidence effects cover about 1,000-1,300 km² of the valley and the maximum vertical displacement is about 1.5 m. As the demand for water continued to increase with population, large imports from the Colorado River via Lake Mead provided abundant water, which helped create additional hazards: a rising shallow water table, resulting from over irrigating landscapes (secondary recharge), intersects land surface in places in the central and eastern part of the valley creating a hazard to structures and facilities; the potential increases in liquefaction; and, the potential for degradation of the deep aquifers from downward percolation of the poorer quality water from the shallow system.