Understanding tile drain discharge dynamics through saturated area observation

This study explored the potential of using saturated area patterns in understanding tile drain response from an agricultural hillslope. Using spatial analysis of time-lapse imagery gathered from the Hydrological Open-Air Laboratory (HOAL) in Petzenkirchen, Lower Austria, twelve events between 2015 and 2017 have been analyzed. Visual inspection of the analyzed events reveals connected or disconnected saturation patterns in the downslope direction of the hillslope. The connected events show consistently larger average maximum connected distance (> 32 m) and average saturated area (> 50 m²) during the events. The results show that for the connected events, tile drain response is always low, while for the events that become connected, the tile drain response increases rapidly with connectivity distance. Overall, the observed saturated areas are shown to outperform traditional explanatory variables of tile drain response, with the exception of event groundwater levels, with a 59% and 62% of behaviour explained for peak tile drain discharge and event volume, respectively. Camera observations are sensitive to snow cover and surface vegetation, which necessitates a manual pre-screening of the captured events for possible use. Overall, the findings of this study suggest that observations of saturated areas are highly informative for predicting hillslope scale runoff and related hydrological processes because they provide spatially distributed rather than point scale information, which presents a cost-effective method with potential of much wider use in hydrology.