The relations between ground water and surface water were studied by the U.S. Geological Survey in the Silver Creek area, Blaine County, Idaho, as part of a comprehensive investigation of the area's water resources. Ground-water withdrawals calculated for 1975 totaled about 16,000 acre-feet (2.0 x107 cubic meters) of pumped ground water and 12,000 acre-feet (1.5x107 cubic meters) of ground water extracted through flowing wells. The ground water is contained in alluvial and basalt aquifers comprised of gravel, sand, and basalt interbedded with fine-grained silt and clay. Nineteen shallow test holes were drilled and cased to define the extent and effectiveness of confining layers in the southern part of the valley. Water-level fluctuations monitored in about 75 wells showed seasonal variations of 40 feet (12 meters) in the northern part of the area and less than 5 feet (1.5 meters) in some wells in the southern part of the area. Numerous stream-discharge measurements were made to define areal and temporal distribution of groundwater discharge. Most of the flow in Silver Creek rises from springs discharging from the shallow aquifer near the edge of the confining beds. Only a small amount of discharge to the creek is attributable to upward movement of water through the confining beds. Discharge from the artesian aquifer near Stanton Crossing may contribute a significant portion of the spring flow which feeds the Big Wood River. Seasonal fluctuations in spring discharges are directly related to fluctuations in ground-water levels. Although losses from Silver Creek downstream from the confining beds were documented during various times of the year, losses were relatively small. A deposit of fine-grained sediments near Picabo effectively perches Silver Creek above the deep basalt aquifer.
