Water Resources Research Act Program

Principal Investigators: Stephan Custer

Abstract: No one is certain how the West Gallatin River interacts with the underlying alluvial aquifer. In 1960 The Gallatin River, from Gallatin Gateway to Logan, was described as a gaining stream by the United States Geologic Survey (Hackett, 1960). The scale of this study encompassed the entire Gallatin Valley and based the gaining stream definition on the rivers net increase in discharge at Logan, where much of Valleys groundwater is forced to the surface before the Gallatin joins the Missouri. The 1960 study is presently the only public study to address how the river and the aquifer are connected. Upstream from Logan the West Gallatins interaction with the underlying aquifer has not been publicly studied. Decisions are being made about water management based upon limited data from the 1960 USGS study or private assessments by hired consulting firms. Does the West Gallatin River gain water, lose water, both, or neither? If it is connected; where is it connected, how it connected, and does its connection change seasonally? Answers to these questions would be very useful for making informed decisions about water resource development in the Gallatin Valley. The goal of this study is to provide answers to these questions for a 10 kilometer reach near Four Corners Montana.