Effects of well discharges on hydraulic heads in and spring discharges from the Geothermal Aquifer System in the Bruneau area, Owyhee County, southwestern Idaho

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Demand for ground water in the 600-square-mile Bruneau study area has increased since 1954 because of agricultural development. Declining flow at Indian Bathtub Spring is adversely affecting a unique species of snail that inhabits the spring. Ground-water development since the mid-1890s locally has modified the direction of water movement in both the sedimentary and volcanic-rock aquifers. In 1989, ground water moved toward four cones of depression created by pumping—two in the northern part of the study area are in the sedimentary-rock aquifer, and two in the southern part are in the volcanic- rock aquifer. Pumping has caused hydraulic heads in the volcanic-rock aquifer to decline more than 30 feet in much of the area and at least 70 feet in one well. About 1 mile from Indian Bathtub Spring, the water level in one well declined about 10 feet during 1979-92, or about 0.7 feet per year. Within the past 25 years, discharge from monitored springs along Hot Creek and the Bruneau River has declined, most notably from Indian Bathtub Spring. Discharge from Indian Bathtub Spring in 1964 was about 2,400 gallons per minute, and by the summer of 1989, discharge was zero. Discharge began to decline in the mid-1960s when the rate of increase in pumpage accelerated. In contrast, discharge from Pence Hot Spring has ranged from about 700 gallons per minute to about 1,100 gallons per minute. Changes in discharge from monitored springs corresponded with changes in hydraulic head, which fluctuates seasonally, and are substantially less in late summer than in the spring. A hydraulic head/spring discharge relation was developed for two sites at Indian Bathtub Spring and a nearby test hole. The relation for Indian Bathtub Spring indicated that a spring discharge of 2,400 gallons per minute would relate to a hydraulic head of about 2,708 feet at the spring, which is about 34 feet higher than the head at zero spring discharge.

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ELECTRONIC FILE - Ecology

SWAP (2/19/2016) citation:
Berenbrock C. 1993. Effects of well discharges on hydraulic heads in and spring discharges from the geothermal aquifer system in the Bruneau area, Owyhee County, southwestern Idaho. Boise (ID): US Geological Survey. (Water-Resources Investigations Report No. 93-4001). [accessed 2015 Jan 12]. http://pubs.usgs.gov/wri/1993/4001/report.pdf