Hillslope-Channel Runoff Connectivity During the North American Monsoon Across an Arid Piedmont Landscape

Abstract:

The frequency with which arid aquifers experience recharge is of interest to stakeholders seeking to ensure water resources. Previous studies using a process-based model and long-term data sets have investigated the water balance in an arid watershed, located in the Jornada Experimental Range, near Las Cruces, New Mexico. In this study, we investigate how focused recharge to aquifers can occur via the runoff generation process on connected hillslope surfaces. Hillslopes are an important transporter of water into ephemeral channels that are sites for focused recharge during the North American monsoon. This summer rainy period is characterized by high-intensity thunderstorms that often lead to the initiation of runoff in connected hillslopes. Understanding the rainfall thresholds at the hillslope scale that lead to hydrologic connectivity between hillslopes and ephemeral channels is integral to understanding groundwater recharge. To do so, we present an analysis of datasets collected in four (4) hillslope runoff plots that include soil moisture at 5, 15 and 30 cm depths, channel runoff via flumes, and precipitation via tipping bucket rain gauges. The hillslope plots have been characterized with respect to elevation and their bare soil and vegetation composition, using near-field remote sensing techniques and structure from motion analysis. We hypothesize that more runoff will be generated via the infiltration excess process on hillslope plots with a larger percentage of bare soil and connectivity between bare soil patches. Inversely, we hypothesize that plants decrease runoff at the hillslope scale by limiting bare patch connectivity and providing more opportunity for reinfiltration to occur, thus limiting contributions to ephemeral channels. By understanding the thresholds of runoff generation in the watershed and with supporting datasets spanning over a decade of rainfall and soil moisture at the site, we aim to shed light on how frequently arid aquifers experience recharge via ephemeral channels.