Linkages between hillslopes, riparian settings, and streamflow: a multi-year, multi-site characterization of spatio-temporal variability in Tenderfoot Creek Experimental Forest

Abstract:

Landscape patterns of shallow water table dynamics are strongly variable, largely driven by the influences of subsurface lateral water redistribution and evapotranspiration. While we recognize that landscape context affects the movement of water through a catchment, we still have a limited understanding of the relationship between water table dynamics and landscape position. Even less understood is how these dynamics vary across many locations, and how they vary year to year, due to the lack of long duration and high frequency water table measurements across a range of landscape positions. To disentangle the relationship between landscape context and response, we analyzed six years of hourly shallow groundwater levels across 26 instrumented hillslope-riparian landscape transitions within the Tenderfoot Creek Experimental Forest (central Montana). To compare shallow groundwater level signals, we extracted several annual metrics related to response magnitude, connectivity, variability, and flashiness. Landscape influence was quantified in terms of statistical descriptors of upgradient topographic distributions across the 26 delineated hillslopes. For all wells, we explored relationships between landscape characteristics and water table response as well as water table response and streamflow. We compared these relationships between years, enabling us to identify parts of the landscape that were more stable versus more variable with respect to climate. Overall, the complex relationships between vegetation, topography, and climate led to variable water table dynamics that are well explained in some locations but widely changing and poorly predicted in others. Observations that span space and time not only improve our understanding of connections between the landscape and the hydrologic behavior it defines, but help to identify where the gaps in our understanding, in both space and time, still exist.