Experimental and numerical investigations of the effect of imbricated gravel structures on flow and solute transport in a highly heterogeneous alluvial-proluvial fan aquifer, SW China

An alluvial-proluvial fan (APF) has heterogeneous characteristics, which result in the development of imbricated gravel channel networks formed by flow erosion. In this type of aquifer, groundwater flow and solute transport are significantly affected by the connectivity of the channels. This paper investigates the 2D connectivity of a heterogeneous APF aquifer based on a case study of the Dali APF and a physical box numerical model in order to determine how the imbricate gravel channel structures, which have different angles of inclination, influence the flow and solute transport under pumping conditions. Our results indicate that the continuity and connectivity among the imbricated gravels and the imbedded clay lenses of the APF aquifer are the key factor controlling the transport and evolution paths of the plume, while the gravel inclination angles influence the first arrival time, the peak arrival time, and the peak concentration of the downstream observation wells. A smaller gravel inclination angle results in a plume with a larger horizontal range and a smaller vertical range. In contrast, a larger inclination angle causes a later peak arrival time and a longer plume tail. This investigation provides insight into flow and transport within imbricated gravel structures and provides a valuable reference for groundwater risk assessment in similar APF aquifers.