Surface and subsurface sensors to record variable runoff generation areas

Hydrologic processes related to runoff generation during rainfall events are being studied in a small ridge and valley watershed in east-central Pennsylvania. To record the dynamics of the near-surface water table (top 45 cm) and the occurrence and dynamics of surface saturation and runoff generation areas, two types of sensors, subsurface saturation and surface runoff, were designed. These two types of sensors are an improvement over an earlier version of saturation sensor. The newly designed subsurface saturation sensor is a printed circuit board with sensing pins to indicate the depth of water-table as it exceeds six different preset depths (1, 5, 10, 20, 30, and 45 cmfrom the surface). The surface runoff sensor; a miniature V-notch weir, is a "yes-no " sensor that indicates whether or not there is surface runoff: Sixty-three subsurface saturation and 42 surface runoff sensors were installed in a 20 m x 40 m hillslope adjacent to a headwater stream, All sensors were connected to data-loggers for automated continuous data collection. This field application proved that these sensors are easy-to-install and cost effective as compared to shallow wells. The performance of the subsurface saturation sensors compared favorably with local shallow wells. Data from these sensors can be used to identity the process(es), saturation excess or infiltration excess, that leads to the occurrence of surface saturation and runoff generation areas over distributed spatial locations. The rime series data from these sensors can be used to identify and define the dynamics of surface saturation and runoff generation areas during rainfall events.