7.0 NATURAL RESOURCES
Natural resources are an important element of the Eureka County economy and the quality of life enjoyed by local residence. Natural resources support many critical economic sectors, provide for community development, enhance the quality of life by supporting recreational activities enjoyed by residents and visitors. One of the most important natural resources in the County is water. In the arid west, water is precious and limited.
Throughout the region, precipitation varies widely between seasons and years as well as within elevation. Annual precipitation ranges from 11 to 13 inches and results mostly from winter storms although summer thunderstorms can produce large amounts of precipitation as rain but contribute little to annual precipitation. Higher amounts of precipitation generally occur as elevation increases. Above 6,000 feet it is not uncommon for areas in central Nevada to receive 14 inches of precipitation or more.
Precipitation supports groundwater recharge. Table 7-1 shows major groundwater hydrographic basins in Eureka County including the active duty groundwater rights and perennial yield of each basin.
Figure 7-1 provides a comparison of active duty water rights, perennial yield and pending actions by the State Engineer. A distinctive feature is the condition where active duty groundwater rights exceed the perennial yield. Diamond Valley is the more extreme case in Eureka County. Table 7-2 shows groundwater rights by type of use in Eureka County hydrographic basins. As shown in Figure 7-2, agriculture followed by mining and milling account for about 93.4 percent of groundwater right usage in Eureka County.
Groundwater Wells and Groundwater Depth
Table 7-3 shows the number of estimated groundwater wells by type of well in each basin. There are nearly 2,300 wells in the Eureka County. The largest category of wells is irrigation and mining. The total number of domestic wells has increased from 220 in 2012 to 251 in 2018.
Groundwater in Eureka County also supports municipal and domestic water demands. There are three municipal systems operated by Eureka County. One is in the Town of Eureka, another in Devilís Gate, and a third in the Town of Crescent Valley. The water systems in Eureka County currently meet all drinking water standards. Arsenic treatment was recently added to the Town of Crescent Valley water system. Overall, the systems in Eureka County are in excellent condition meeting all municipal operating standards. Figure 7-3 shows the number of water customers in each system. Since 2010, there has been limited growth in the number of municipal customers served by the systems, although the Town of Eureka is trending higher.
Historic Water-Level Changes
Water levels in the Diamond Valley Flow system have changed over time as a result of withdrawals for irrigation, municipal, domestic, and mining uses and as a result of annual long-term variations in precipitation. Most withdrawals have been for irrigation in southern Diamond Valley where the irrigated area expanded from 3,200 acres in 1961 to 22,200 acres in 1990. Water level declines from the 1960s to 2005 in southern Diamond Valley ranged from 26 to 90 feet at 67 wells. The large area of water-level decline that has been developed in the basin-fill aquifer of southern Diamond Valley underlies an area about 10 miles wide and 20 miles long.
Long-term water level records are available for only a few wells in Kobeh, Monitor, and Antelope Valleys. Kobeh Valley water levels ranged from 35-46 feet below the land surface with minor annual fluctuations generally 2-4 feet. In Monitor Valley water levels ranged from 48 to 56 feet below the land surface with limited annual fluctuations and response to short-term changes in precipitation. In northern Antelope Valley water levels ranged from 94 to 98 feet below the land surface with annual fluctuations of less than 1 foot (USGS Scientific Investigations Report 2006-5249).
Figure 7-4 shows changes in depth of groundwater since 1960 for a USGS monitoring well in Diamond Valley. Overall declines of about 100 feet have occurred since 1960. This trend is consistent with several wells in the area. Figures 7-5 and 7-6 show recent trends in wells being measured by Eureka County.
The major surface water feature in Eureka County is the Humboldt River which has an average annual discharge of approximately 218,000 acre-feet. Other major surface water features include Pine Creek and a series of smaller perennial streams originating in the Roberts Mountains, the Diamond Mountains, Cortez Range, and Monitor Range. Stream flow readings are limited in Eureka County. In recent years the United States Geologic Survey installed gauging stations at streams in the Roberts Mountains. The following graphs show real-time daily readings for Roberts Creek, Henderson Creek, Pete Hanson Creek, Tonkin Springs and Colis Creek through June 2018. Drought conditions from 2012 to 2016 reduced stream flows.
Precipitation in Eureka County (Antelope Valley) is shown in Figure 7-7. The average annual precipitation as measured at Antelope Valley between 1955 and 2012 is 12.74 inches. The wettest ten-year period was 1980 to 1990 followed by 1990 to 2000 averaging 13.1 and 12.8 inches respectively. The period of 2000-2017 saw an average of 12.54 inches.
Figure 7-8 shows the historic average precipitation and the extreme recorded precipitation by month. The spring months of March, April, and May have the highest average precipitation and extreme high precipitation amounts.
Figure 7-9 shows average high and low temperature as well as the highest and lowest extreme temperatures recorded since 1931. Temperature in Eureka County has large variations from highs to low creating average temperatures which appear to be somewhat moderate. The extreme recorded temperatures show a 151-degree range.