Saturation area connectivity in the Hydrological Open Air Laboratory

Surface runoff from agricultural hillslopes is one of the most important factors controlling soil erosion, land degradation and stream water contamination. In order to improve the understanding of surface runoff, studying the connectivity of flow paths and the different properties present in them is necessary for a more complete understanding of system behaviour. This study aims to analyze the structural connectivity scale index on an agricultural hillslope based on time-lapse photography. The study is conducted on a 26.8 ha hillslope at the Hydrological Open Air Laboratory (HOAL) experimental catchment in Austria. Using digital camera observations, the temporal dynamics of connectivity are estimated from the time-lapse photography for the period of 2014-2020. In order to study the impact of the saturated areas, directly measured field data (precipitation, soil moisture, discharge), and its change, was analyzed in relation to the connectivity scale timeseries. The main driving factor for the generation of the saturated areas are the antecedent conditions of the soil. It was found that there is a significant correlation (r²: 0.83) between maximum sediment output in the stream and the detected integral connectivity scale values. Furthermore, the 5-minutes timeseries of sediment discharge and connectivity scale were compared, which resulted in a set of unimodal cross-correlations with the peak located in the 0-50 lag domain; physically, this implies a consistent 0-4 h delay in the catchment response, varying through events.