Assessment of piping-sinkhole development in a fluvial-terrace scarp retreat environment: A multi-temporal analysis on the lower Ticino River (Italy)

This paper investigates, from a geomorphological and hydrogeological point of view, the development of piping-sinkhole phenomena at a retreating fluvial-terrace scarp along the lower Ticino River, near Casottole, northern Italy. Piping forms and features are well documented in the literature as complex soil erosion phenomena, usually associated with clayey or carbonate substrata, or to specific fluvial deposits. Such phenomena appear to have never been mapped in the lower Ticino area, and up to now, no evidence of piping-sinkhole occurrence in terraced alluvial plains strictly associated with terrace scarp erosion processes have been observed and reported in the literature. The geomorphological peculiarities of the area were assessed through field surveys, photographic and drone imaging, photointerpretation, and GIS analysis. Moreover, the riverbed morphological evolution was evaluated since the 1950s, and the hydrogeological conditions were analysed. Finally, a large piping-sinkhole database composed by 35 landforms was assembled in a WebGIS system. The piping-sinkhole phenomena were associated with the presence of perched water tables with flows towards the Ticino River, whose origin can be associated with site conditions, the large up dip network of surface water, and local irrigation practices. The research presented here provides a new contribution to the understanding of sinkhole occurrence and formation in previously unstudied terrace-scarp settings, and new insights for fluvial-terrace scarp modelling. Furthermore, it represents an important knowledge base to inform sustainable and effective measures for environmental management and hydrogeomorphic risk mitigation with reference to terrace scarp erosion and sinkholes.