University of Montana, Maureen and Mike Mansfield Library
Abstract
Streamflow and groundwater response to snowmelt in forested subalpine catchments carry integrated information about snowmelt events within the basin at different temporal scales. High frequency snowmelt events are often dominated by the day-night cycle, which is reflected in groundwater and streamflow dynamics. Prior studies have highlighted the importance of sub-daily streamflow fluctuations in these catchments for nutrient cycling, riparian aquifer pumping, and surface water availability. In studies that predict stream response to snowmelt or precipitation, sub-daily fluctuations in hillslope water storage are rarely considered as a tool to assess the role of hillslopes in moderating stream recharge from snowmelt runoff over sub-daily timescales. In this study we compare high frequency (15-minute) atmospheric radiation and its influence on the timing and magnitude of both water table and stream stage fluctuations. We analyze net radiation over the snowpack to approximate the energy state of the snowpack and relate it to hillslope hydrologic response and changes in stream stage. Our results suggest that the snowpack cold content must be overcome on a daily basis before recharge to the soil can occur. Until the snowmelt process is resumed, both hillslope water storage and stream stage decrease. We conceptualize the process as a linear series of energy and water reservoirs that fill and deplete driven by the daily atmospheric cycle. By measuring the timing of diurnal peaks in radiation, groundwater response, and stream stage over an entire melt season, we assess the role of the snowpack and hillslopes as filters that moderate and delay the movement of water from the top of the snowpack to local stream systems. Our interpretation of shifts in the timing of diurnal peaks in groundwater and stream stage suggests that once hillslopes become saturated in the uppermost 50 cm of soil, the energy state at the top of the snowpack, the physical properties of the snowpack, and the length of the hillslope that is saturated determine the timing of stream recharge from diurnal snowmelt events. Finally, we present two conceptual models that capture hillslope- and watershed-scale processes that moderate stream recharge during the spring melt season
