Trends in flow of the Humboldt River, North-Central Nevada, 1945 to 2020

The Humboldt River flows from its headwater areas east of Elko to the Humboldt Sink southwest of Lovelock. Water in the river is used primarily for irrigation of crops and the river has been fully appropriated and adjudicated since the 1930’s. Groundwater pumping for irrigation began increasing in the 1960’s. Dewatering of mines began in the early 1990’s. Pumping of groundwater has raised concerns over its effects on flow in the river, particularly during periods of drought. Five continuously operated gaging stations on the Humboldt River were used to evaluate if groundwater pumping since the 1960’s could be causing a decrease in flow. Various analysis using annual, monthly, and daily flows at Humboldt River gaging stations indicate flow between the Comus and Imlay gaging stations showed an increase in loss that exceeded estimated measurement errors. The mean difference in flow between gaging stations during two droughts—water years (WYs) 1953 to 1955 and 2012 to 2015 also indicate increased loss between the two gaging stations. Daily mean flows at the gaging stations show little difference between October 1945 to September 1969 and January 2007 to September 2020 except for the Imlay gaging station where the daily mean flow for the latter period was less 90 percent of the time than the earlier period. The lack of a change in flow at the Comus gaging station is consistent with the number of days when daily mean flow at the gaging station was less than 1 cubic foot per second (cfs) for two 13-year periods with nearly the same mean flow (1,297 days during WYs 1951 to 1964 and 1,291 days during WYs 2007 to 2020). However, the number of days when the daily mean flow at the Imlay gaging station was less than 1 cfs increased from 64 days during the earlier period to 941 days during the later period. In conclusion, flow at gaging stations upstream of Comus indicates no measurable decrease that could be attributed to groundwater pumping, whereas a measurable decrease in flow at the Imlay gaging station is best explained by groundwater pumping near the river downstream of Comus.