The High Variability of Hydrologic Response in Mountain Watersheds: Snowy Range, Wyoming

Abstract:

Three adjacent mountain streams that coalesce to form a single river have been monitored with a nested watershed design comprised of ten runoff stations for the past three years. Some of the stations are co-located on previous monitoring sites that allow for an extended period of record. Stage-discharge relationships have been built with high degrees of confidence at each station, and stream isotope data have been taken to better determine sources of water and fractionation of precipitation into runoff components. In addition to runoff observations we have multiple weather stations and use geophysical methods to investigate the subsurface and better characterize potential flow pathways and remote sensing and field methods to characterize the watersheds. From these data we have observed a high degree in variability in runoff characteristics among these sites, including significant differences in annual runoff, proportion of baseflow, rainfall/runoff efficiency, and hydrologic regime. Analyses of nested runoff data reveal longitudinal and seasonal changes in surface and subsurface flow, which allow us to identify the timing and location of groundwater contributions and channel transmission to regional aquifers. Differences among the watershed responses are augmented by precipitation, and we identify stream reaches that change from effluent to influent depending on timing and magnitude of runoff. We explored physical interpretations for the observed variability, including management, beetle impacts, and subsurface characteristics as inferred from geophysical data.