Abstract
Understanding hillslope runoff response to intense rainfall is an important topic in hydrology, and is key to correct prediction of extreme stream flow, erosion and landslides. Although it is known that preferential flow processes activated by macropores are an important phenomena in understanding runoff processes inside a hillslope, hydrological models have generally not embraced the concept of an extra parameter that represents ‘macropores’ because of the complexity of the phenomenon. Therefore, it is relevant to investigate the influence of macropores on runoff processes in an experimental small artificial hillslope. Here, we report on a controlled experiment where we could isolate the influence of macropores without the need for assumptions regarding their characteristics. Two identical hillslopes were designed, of which one was filled with artificial macropores. Twelve artificial rainfall events were applied to the two hillslopes and results of drainage and soil moisture were investigated. After the experiments, it could be concluded that the influence of macropores on runoff processes was minimal. The S90 sand used for this research caused runoff to respond fast to rainfall, leading to little or no development of saturation near the macropores. In addition, soil moisture data showed a large amount of pendular water in the hillslopes, which implies that the soil has a low air entry value, and, in combination with the lack of vertical flow, could have caused the pressure difference between the matrix and the macropores to vanish sooner and result in equilibrium being reached in a relatively short time. Nevertheless, a better outline is given to determine a correct sand type for these types of experiments and, by using drainage recession analysis to investigate the influences of macropores on runoff, heterogeneity in rainfall intensity can be overcome. This study is a good point of reference to start future experiments from concerning macropores and hillslope hydrology.
Highlights
The complexity of hydrological processes at hillslope and small catchment scales during periods of water input is still not well understood in spite of all the extensive research during the past several decades [1,2,3,4]
This study aimed to investigate if a laboratory experiment can be produced to examine the influence of macropores on runoff processes inside a hillslope, and whether macropores influence the hydrological response of a small artificial hillslope
Some improvements can be made for future experiments, and it should be taken into consideration if other mechanisms like overland flow, infiltration capacity and varying rainfall intensity are as important to investigate
Summary
The complexity of hydrological processes at hillslope and small catchment scales during periods of water input is still not well understood in spite of all the extensive research during the past several decades [1,2,3,4]. It is known that preferential flow processes activated by macropores are an important phenomena in understanding runoff processes inside a hillslope, hydrological models have been slower to embrace the concept of an extra parameter that represents ’macropores’ [11,12]. Some models did try to incorporate macropores through a modification of the hydraulic conductivity. This approach is substantially different from describing the preferential flow paths that macropores create [13,14,15]. This approach is often chosen because of the complexity of the phenomenon
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