Spatial-Temporal Patterns of Preferential Flow Occurrence In the Shale Hills CZO Based on Real-Time Soil Moisture Monitoring.

Preferential flow initiation and persistence is the critical hydrological process resulting in rapid fluxes of water and contaminants from hillslopes and swales laterally to the stream channel and vertically to the water table.  While the controls on preferential flow have been studied extensively, research has traditionally focused on individual irrigation experiments, excavations, and limited storm monitoring.  We have analyzed over 3 years of soil moisture and precipitation monitoring, identifying over 160 distinct storms.  For each storm we have identified the soil moisture response at 10 sites and categorized the response as preferential flow, sequential response or indeterminate.  Preferential flow is defined as a non sequential response to precipitation with depth.  Sequential flow is thought to be indicative of a vertical wetting front from the soil surface to depth.  From these analyses, in conjunction with analysis of the precipitation and soil moisture dynamics prior to and during the storm, we are able to develop a comprehensive understanding on the controls on preferential flow at the Shale Hills Critical Zone Observatory, a forested catchment in central Pennsylvania.  In addition, we will demonstrate methodology for determining preferential flow from long term time series of soil moisture measurements.