Summary of the Snake River plain Regional Aquifer-System Analysis in Idaho and eastern Oregon

Location and timing of river-aquifer exchanges in six tributaries to the Columbia River in the Pacific Northwest of the United States

“…Along the Snake River around Thousand Springs (RK 953 to 914), the thickness of the Quaternary basalt decreases from more than 1000 m to less than 30 m and the river incises a 200-m-deep canyon below the surrounding plain (Lindholm, 1996). The Snake River Plain narrows from 100 to 35 km as older (Tertiary) volcanic rocks impinge from the north and south.…”

“…Lindholm (1996) noted that the Snake River gained flow from RK 1020 to 872 as it incises 200 m below the adjacent land surface through the Snake River basalt. Likewise, Gannett et al (2001) observed that the Deschutes River gains flow from RK 209 to 206 where it incises into the Deschutes Formation.…”

Scientific Drilling

“…The electrical resistivity (ER) maps are thought to define the depth to water-saturated basalt-generally interpreted to represent the base of the younger Quaternary basalts, excluding older Pliocene basalts which have limited porosity (Lindholm, 1996). Our data suggest that the ER measurements most likely correspond to the base of the Snake River aquifer.…”

“…. Lindholm (1996) used potential field, resistivity, and well data to infer a basalt thickness of 1.2-1.4 km in the axial volcanic zone (Fig. 1).…”

Introduction to the hydrogeology of the eastern Snake River Plain

“…The hydraulic gradient is ϳ0.6-19 m/km and averages ϳ2.3 m/km (Lindholm et al, 1988). Gradients are smallest in the central part of the plain southwest of the INEEL, where there is a thick section of transmissive basalt (Lindholm, 1991). Water moves horizontally through basalt interflow zones and vertically through joints and interfingering edges of interflow zones.…”