HYDROLOGIC IMPLICATIONS OF GREATER GROUND‐WATER RECHARGE TO LAS VEGAS VALLEY, NEVADA¹

Abstract

Published estimates of natural recharge in Las Vegas Valley range between 21,000 and 35,000 acre‐feet per year. This study examined the underlying assumptions of previous investigations and evaluated the altitude‐precipitation relationships. Period‐of‐record averages from high altitude precipitation gages established in the 1940s through the 1990s, were used to determine strong local altitude‐precipitation relationships that indicate new total precipitation and natural recharge amounts and a new spatial distribution of that recharge. This investigation calculated about 51,000 acre‐feet per year of natural recharge in the Las Vegas Hydrographic Basin, with an additional 6,000 acre‐feet per year from areas tributary to Las Vegas Valley, for a total of 57,000 acre‐feet per year. The total amount of natural recharge is greater than estimates from earlier investigations and is consistent with a companion study of natural discharge, which estimated 53,000 acre‐feet per year of outflow. The hydrologic implications of greater recharge in Las Vegas Valley infer a more accurate ground‐water budget and a better understanding of ground‐water recharge that will be represented in a ground‐water model. Thus model based ground‐water management scenarios will more realistically access impacts to the ground‐water system.

A REEVALUATION OF THE GROUND WATER BUDGET FOR LAS VEGAS VALLEY, NEVADA, WITH EMPHASIS ON GROUND WATER DISCHARGE1

“…Previous investigators such as Maxey and Jameson (1948) and Malmberg (1965) assumed there was no ground water being discharged out of the valley, however, Malmberg did map phreatophytes along the wash to the vicinity of Three Kids Wash. Harrill (1976) estimated 1,200 AFY (1,480,176 m 3 ) of ground water exiting the valley under Frenchman and Sunrise Mountains, 2 to 5 miles (3.2 to 8.0 km) north of the wash. Morgan and Dettinger (1994) estimated ground water discharge at 1,500 AFY (1,850,220 m 3 ) from the valley at the same location designated by Harrill (1976) and an additional 500 AFY (616,740 m 3 ) discharged through sediments underlying Las Vegas Wash. Donovan and Katzer (2000) estimated 6,000 AFY (7,400,880 m 3 ) of outflow in this same area.…”

“…Thus the estimate for natural ground water outflow would be in the range from 1,200 to 16,000 AFY (1,480,176 to 12,735,680 m 3 ), with estimates generated in this study ranging from 8,000 to 16,000 AFY (9,867,840 to 19,735,680 m 3 ). This changes the water budget for LVV defined by Donovan and Katzer (2000), who used an estimate of 6,000 AFY (7,400,880 m 3 ) for outflow, but it does not change the amount of ground water recharge, which is briefly discussed here for continuity and to present a revised ground water budget.…”

“…Another statewide precipitation map was published by the Oregon Climatic Service (Daly et al, 1994;Daly et al, 1997) using the period of record from 1961 to 1990. Donovan and Katzer (2000) published yet another precipitation map of just LVV in the form of altitude precipitation relationships using local in-valley stations, including recently (1984) installed high altitude precipitation stations, that more accurately represents total annual precipitation. Precipitation totals from these three maps for LVV are compared in Table 3.…”

“…Other investigators in LVV used different techniques or variations of the Maxey-Eakin method, and these are compared in Table 4. Donovan and Katzer (2000) also used a slight variation of the Maxey-Eakin method to estimate ground water recharge from precipitation for LVV even though it is nonunique and empirical, and was developed using the earliest precipitation map by Hardman (1936). Despite limitations of the methodology, it appeared to work well with the new altitude precipitation relationships.…”

“…Even more recent investigations using geochemistry techniques (Dettinger, 1987;Thomas et al, 1996) estimated natural recharge by using precipitation estimates by Harrill (1976). The natural recharge for LVV has been reevaluated recently by Donovan and Katzer (2000) and shows an increase ranging from about 1.5 to nearly three times any previous investigator's estimates.…”