Budgets and Chemical Characterization of Groundwater for the Diamond Valley Flow System, Central Nevada

Science Center Objects

The Diamond Valley flow system (DVFS) consists of six basins or hydrographic areas (HAs) in central Nevada: southern and northern Monitor Valleys, Antelope Valley, Kobeh Valley, Stevens Basin, and Diamond Valley. The six basins are, in part, hydrologically connected by ephemeral streams, by groundwater flow in shallow basin-fill aquifers, and, possibly, by subsurface flow in deeper carbonate-rock aquifers. Local government officials and citizens are concerned about the continuing development of water resources for irrigation and mining and about the potential for groundwater exportation to basins outside the DVFS.

desert landscape with clouds and mountains in distance

Kobeh Valley (Public domain.)

In 2005, the USGS Nevada Water Science Center, in cooperation with Eureka, Lander, and Nye Counties and the Nevada Division of Water Resources (NDWR) began a three-phased study of the flow system to gain a better understanding of the groundwater resources. Phase 3 (2009–12) was the final phase of work designed to build on and further characterize the groundwater resources of the flow system by evaluating groundwater quality and groundwater budgets, with emphasis on groundwater evapotranspiration(ET) by phreatophytes (plants that rely on groundwater to fulfill a part of their water needs) under predevelopment conditions.

Groundwater chemistry was characterized using major ions and stable isotopes from groundwater and precipitation samples.

scientist sampling groundwater in kobeh valley

Measuring water levels in a well in Kobeh Valley (Public domain.)

  • Groundwater in the basin-fill aquifer of the Diamond Valley flow system was mostly a calcium or sodium bicarbonate water type and generally within acceptable drinking-water standards. The general water type was similar among the individual hydrographic areas.

Groundwater budgets accounted for all inflows, outflows, and changes in storage, and were developed for predevelopment (pre-1950) and recent (average annual 2011–12) conditions. Major budget components include

  • groundwater discharge by ET and net groundwater withdrawals;
  • groundwater recharge by precipitation, and interbasin flow (subsurface inflow or outflow); and
  • storage change.

GROUNDWATER DISCHARGE AND WITHDRAWALS

east et station in kobeh valley

Kobeh Valley East Evapotranspiration Station (Public domain.)

Site-scale groundwater ET was estimated from eddy-covariance and micrometeorological measurements collected at four sites.

  • ET ranged from 0.15 feet per year in sparse, undisturbed shrubland to 1.13 feet per year in a grassland meadow.

Vegetation indices calculated from satellite imagery and field mapping were used to define three ET units (shrubland, grassland, and playa) and to extrapolate site-scale groundwater ET rates to basin-scale estimates.

  • Annual pre-development groundwater ET for individual hydrographic areas ranged from 2,900 acre-feet per year (acre-ft/yr) in northern Monitor Valley to 35,000 acre-ft/yr in Diamond Valley.
  • Total groundwater ET from the Diamond Valley flow system under pre-development conditions was about 70,000 acre-ft/yr.

Areas of irrigated land in the Diamond Valley flow system increased from less than 5,000 acres in the early 1960s to more than 25,000 acres in 2012 and are mostly for growing alfalfa in southern Diamond Valley.

  • Annual (2011–12) net groundwater withdrawals for irrigation, assumed to be the volume of groundwater consumed by crops and pastureland, ranged from about 420 acre-ft/yr in Antelope Valley to 67,000 acre-ft/yr in Diamond Valley.
  • Total net groundwater withdrawals for irrigation in the Diamond Valley flow system were about 69,000 acre-ft/yr (2011–12).

GROUNDWATER RECHARGE AND INTERBASIN FLOW

Groundwater recharge, the largest inflow component to the Diamond Valley flow system, was determined as the sum of groundwater ET and net subsurface outflow (subsurface outflow minus subsurface inflow).

  • Annual groundwater inflow estimates ranged from 200 acre-ft/yr in Stevens Basin to 35,000 acre-ft/yr in Diamond Valley.

Subsurface flow between hydrographic basins was evaluated using estimated transmissivity, groundwater-flow sections derived from remotely sensed imagery, and hydraulic gradients determined from 2012 water-level data.

  • Subsurface outflow ranged from 0 acre-ft/yr for Diamond Valley to 3,400 acre-ft/yr for northern Monitor Valley into western Kobeh Valley.
  • Subsurface inflow ranged from 0 acre-ft/yr for several valleys to 4,200 acre-ft/yr for Kobeh Valley from northern Monitor and Antelope Valleys.

GROUNDWATER BUDGET

The pre-development groundwater budget for the Diamond Valley flow system was estimated at about 70,000 acre-ft/yr of inflow and outflow. During years 2011–12, inflow components of groundwater recharge from precipitation and subsurface inflow from adjacent basins totaled 70,000 acre-ft/yr for the DVFS, whereas outflow components included 64,000 acre-ft/yr of groundwater ET and 69,000 acre-ft/yr of net groundwater withdrawals, or net pumpage. Spring discharge in northern Diamond Valley declined about 6,000 acre-ft/yr between pre-development time and years 2011–12. The overall groundwater budget for the DVFS under recent (2011–12) conditions was not in balance.