Evaluation of Streamflow Depletion Related to Groundwater Withdrawal, Humboldt River Basin


Historically, water users relied heavily on surface water and to a lesser extent on groundwater, primarily for agricultural operations. By the 1930’s, surface water resources were fully allocated prior to groundwater development. Groundwater withdrawals for irrigation began in the 1950’s and gradually increased to more than 150,000 acre-ft/yr by the early 1980's. Beginning in the early 1990’s, groundwater dewatering, as part of open-pit gold mining, significantly increased total groundwater withdrawals within the middle Humboldt River basin.

Nevada water law is based on two fundamental concepts. Prior appropriation, or “first in time, first in right,” ensures senior water users are protected even as new uses for water are allocated. The second concept deals with beneficial use of appropriated water. A water-right permit may only be granted for beneficial uses, which includes irrigation, mining, and municipal uses among others. The Nevada State Engineer is responsible for administering and enforcing Nevada water law. The State Engineer uses the concept of perennial yield to help guide decisions dealing with withdrawal and allocation of groundwater.

Perennial yield is generally defined as the maximum amount of groundwater that can be withdrawn on an annual basis without depleting the groundwater reservoir. In groundwater basins with a flow through river system, like the Humboldt River Basin, perennial yield becomes much more difficult to quantify because base flow may be supported by groundwater, or alternatively, the river may supply water to the groundwater aquifer. Thus, the more recent development of groundwater may be utilizing some of the same water allocated for surface water.