Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/1999
Publication Date: 3/1/2000
Citation: Srinivasan, M.S., Wittman, M.A., Hamlett, J.M., Gburek, W.J. 2000. Surface and subsurface sensors to record variable runoff generation areas. Transactions of the ASAE. 43(3):651-660. Interpretive Summary: A field study to characterize the dynamics and occurrence of areas that produce runoff has been initiated within a small watershed, the Brown Watershed, in east-central Pennsylvania. The humid-climate and fractured- bedrock conditions of the Brown Watershed are typical of upland watersheds of the Northeast U.S. To record the watershed dynamics, innovative subsurface saturation and surface runoff sensors were designed and developed. The subsurface saturation and surface runoff sensors record the fluctuations in the near-surface water table and occurrence of runoff generation areas during rainfall events, respectively. These sensors were installed in a hillslope adjacent to a headwater stream within the Brown Watershed. The sensors were easy to install and cost effective as compared to fully instrumented shallow wells. Data from these sensors will be useful in defining the mechanisms of runoff generation, pathways of runoff, ,and influence of near-surface water table on runoff generation processes. These data provide a basis to evaluate hydrologic concepts and computer simulation models needed to identify critical areas of runoff, erosion, and phosphorus movement from the land surface to streams.
Technical Abstract: Hydrologic processes related to runoff generation during rainfall events are being studied in a small 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 cm from 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 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 identify the conditions of saturation excess and/or infiltration excess that lead to the spatially distributed occurrence of surface saturation and runoff generation areas over the watershed.