Groundwater Careful management of groundwater, the state's long term water supply source, is vital to economic and ecological sustainability. Hydrologists estimate that three to seven percent of the average annual precipitation recharges groundwater systems. Surface water resources are essentially fully appropriated, so new development projects often tap into groundwater sources or seek to transfer existing surface or groundwater rights. Groundwater provides about 40 percent of the total water supply used in Nevada, and groundwater is the sole supply source in some regions. Twenty-eight percent of the state's municipal and industrial water needs are met with groundwater (Nevada Division of Water Planning, 1999). However, the amount of groundwater used can vary considerably each year. More new groundwater wells are being constructed to supplement surface water sources. During periods of low streamflow, groundwater use increases, and conversely, decreases during high flow periods. Proper planning and management of groundwater resources grows in importance as more communities and industries come to depend on this finite resource. Because the state's population and economy is projected to continue to rapidly grow, greater scientific understanding of groundwater conditions will be essential. Particularly, greater knowledge is needed in aquifer location, refined perennial yield, recharge, storage volume, committed resources (water righted amounts), actual water use, water levels, water quality, and projected trends. Forty years ago, the Nevada Division of Water Resources (NDWR) and the U.S. Geological Survey (USGS) recognized the need for a systematic identification of the states "hydrographic areas". A cooperative groundwater program was initiated to study, research, develop, manage, and administer groundwater and surface water systems. A product is the 1968 hydrographic unit map, the first systematic delineation of all hydrographic regions and areas. With minor revisions, the 1968 map continues as the basis Nevada Hydrographic Region Map Click to View HTML File for water planning, management, and administration. The current map delineates 14 hydrographic regions subdivided into 256 hydrographic areas (HA's) (Figure 2-6 ). Another result of the cooperative program was reconnaissance level estimations of perennial yield for each HA. Perennial yield is the estimated volume (acre feet) of usable water in a groundwater basin or aquifer that can be economically withdrawn and consumed each year for an indefinite period without depleting (mining) the source. The State Engineer uses perennial yield estimates as the baseline to compare total committed groundwater allocations to water available in the system, or uncommitted resources (see Figure 2-6 below) Figure 2-6 Estimated Uncommitted Groundwater Resources for Hydrographic Units acre feet per year Click for Adobe PDF File -- 200KB Technically, the calculation method subtracts the amount of water evaporated and transpired (i.e., water vapor from plants) from the amount that may be appropriated. Basins include one or more aquifers, or water-filled cracks, joints, and pores in consolidated volcanic, granitic, or sedimentary rock formations or thick, unconsolidated valley sediment deposits formed by upland erosion. Some aquifers in Nevada contain water recharged thousands of years ago under much wetter climate conditions. Recharge rates under current conditions are much lower. If over-pumped, groundwater levels may be irreparably lowered. Figure Figure 2-7 Estimated Committed Water Resources for River Basins And Hydrographic Regions acre feet per year Adobe PDF File -- 124KB According to the cooperative studies performed by the State Engineer and the USGS, the statewide perennial yield totals about 2.1 million acre-feet per year (Nevada Division of Water Planning, 2001a). "Committed resource" refers to the total volume of groundwater rights that the State Engineer officially recognizes and that usually can be withdrawn from a basin each year (Figure 2-7 -- Adobe PDF File, 124KB). In 1995, groundwater withdrawals total approximately 1.6 million acre-feet statewide. Of the quantity of groundwater pumped, about 0.7 million acre-feet used consumptively. When making determinations on groundwater right applications, the State Engineer considers the individual and regional perennial yield estimates, system yield estimates, and committed resources, among other factors. Committed volumes of water remain lower than perennial yield in about 60 percent of the 256 basins. The state's un-appropriated groundwater supplies are located in these basins. The State Engineer has increased administrative efforts in many of the groundwater basins where demand for groundwater supplies has grown. The State Engineer has authority to "designate" a groundwater basin that is being depleted or requires additional administration to make sure important local uses of the aquifer(s) can be sustained. Figure 2-8 Non-Designated and Status of Designated Hydrographic Units in Nevada Adobe PDF File -- 350KB By issuing an order of designation, the State Engineer is granted additional authority to make special administrative decisions regarding groundwater resources. For example, the State Engineer may issue orders that define preferred uses, deny certain water uses, or curtail pumpage. Preferred uses may include domestic, municipal, quasi-municipal, industrial, irrigation, mining and stock-watering uses or any other beneficial use. Each basin is managed as a separate unit. The State Engineer issues orders and rulings, as needed for the management of the groundwater resources. Figure 2-8 displays the "designated basin" status for the 256 hydrographic units. This map is a useful tool to generally determine where the greatest impediments to groundwater development may exist. However, the associated State Engineer's orders and rulings need to be examined for a complete understanding of the management issues and water availability within a basin. Figure 2-9 Number of Domestic and Public Supply Wells Drilled in Nevada 1984 - 2000 The number of new well logs filed each year gives some indication of the intensity of groundwater development. Figure 2-9 shows the trend in the number of new domestic and supply wells drilled each year since 1984. In 1984, 817 wells were drilled. Since the peak year (1996) when 2,527 wells were drilled, activity has leveled off, ranging between 2,028 and 2,155 each year. Wells drilled for other purposes, such as geothermal production, monitoring, and mineral or future water supply exploration, are not included. The increased well construction activity for domestic and public supply is greatest in areas experiencing rapid growth (i.e., northcentral, northwestern, and the southern regions). Next Page -- Water Supply for Future Needs Back to Table of Contents