The Influence of Topography and Spatial Patterns of Soil Hydraulic Conductivity on Groundwater Response Across a Forested Hillslope

Abstract:

Hydrologic connectivity represents the development of a transient water table between hillslopes and streams and is a requisite for discharge in forested mountain landscapes. Many studies have indicated that topographic convergence of hillslope area leads to more sustained hydrologic connectivity. However, we still do not fully understand how soil heterogeneity may lead to differences in subsurface flow rates, and therefore runoff contributions, across hydrologically connected hillslope positions. To address this knowledge gap we collected 260 measurements of saturated hydraulic conductivity (Ksat) across a 350,000 m² hillslope in the Lubrecht Experimental Forest, MT, USA. We will compare the spatial patterns of Ksat to shallow groundwater responses across a network of 30 recording wells and changes in streamflow measured at the base of the hillslope. Our preliminary analyses indicate that Ksat is reduced in topographic low points relative to planar and divergent positions. These are also locations that exhibited more sustained hydrologic connectivity and elevated shallow groundwater heights. These initial observations suggest a potential linkage between landscape topography, soils, hydraulic conductivity and the duration and rate of hillslope runoff contributions to streams.