Comment on egusphere-2022-165

Abstract

The surface of the earth is constantly changing, especially in mountain areas, where glacial retreat uncovers large bodies of unconsolidated sediment. However, our knowledge on overland flow (OF) generation and related sediment transport is still limited, partly due to a lack of methods to trace the pathways of water and sediment on the surface. To investigate how different surface characteristics affect hydrological- and sediment connectivity on natural hillslopes, we studied five plots on two moraines of different ages in a proglacial area of the Swiss Alps. On all plots, we performed sprinkling experiments to determine OF characteristics, i.e., total OF, peak OF flow rate, peak turbidity and sediment concentrations, and total sediment yield. Here we test if a fluorescent sand tracer, together with UV lamps and a high-resolution camera, can be used to visualize the pathways of OF and to determine the typical sediment transport distances. The results highlight the ability of the setup to detect sand movement, even for individual fluorescent sand particles (300–500 µm grain size), and to distinguish between the two main mechanisms of sediment transport: OF-driven erosion and splash erosion. The experiments also revealed that the higher rock cover on the younger moraine enhanced surface hydrological connectivity and resulted in larger sediment transport distances. In contrast, the higher vegetation cover on the older moraine promoted infiltration and reduced the length of the surface flow pathways and erosion. The study, thus, demonstrates the potential of the new method to improve the observation of surface hydrological connectivity and sediment transport. These observations can help to improve our understanding of OF and sediment transport in complex natural settings.