Soil Pipes: Hydrological Functioning in Loess-derived Soils in a Temperate Humid Climate

Hydrological functioning of natural soil pipes and their impact on water transfer at the hillslope and small watershed scale are still little documented. This is particularly the case for piping in the loess-derived soils of western Europe (temperate humid climate). This paper presents results from a hill-slope study investigating the main processes and factors controlling pipeflow response to rainfall in the Gueule valley (eastern Belgium). The adopted methodology relies on isotopic analyses to determine the origin of water as well as clustering analyses of time series of rainfall, groundwater levels and pipeflow discharge. Results show that pipeflow response to rainfall is driven by a combination of preferential vertical infiltrations directly into the pipe network and into the groundwater, whose rising feeds the pipe network in return. They also highlight a complex threshold-like relationship between pipe discharge and rainfall, mainly controlled by seasonal differences in groundwater levels and to a lesser extent by antecedent wetness of the hillslope. Although some important similarities with other hydrological contexts were found, this study demonstrates that the level of connectivity between the pipe network and the groundwater is key to better understand its response and seasonal behavior. Finally, pipeflow appears to provide strong hydrological connectivity between the upstream and downstream parts of the hillslope, a by-pass role that may have important implications for runoff generation and solute transport at the small watershed scale and requires further investigation.