Spatial variability of vertical hydraulic conductivity of riverbed sediments in the middle and lower reaches of the Luan River in China

Middle and lower reaches of the Luan River in China. The vertical hydraulic conductivity ( K v ) of riverbed sediments serves as a key hydrogeological parameter for assessing quantitatively the exchange of fluxes between rivers and groundwater systems. In this study, we obtained K v in riverbed sediments through in-situ falling head permeameter tests and used geostatistical methods to analyze the spatial variability of K v along the longitudinal (the direction of the river), transverse, and vertical direction of the river. K v significantly decreases longitudinally, from 192.71 m/d midstream to 3.20 m/d downstream. Transversely, it generally reduces from the riverbed center to the banks, while in meandering channels, K v is highest on the outside bend (erosion side) and lowest on the inside bend (deposition side). Vertically, K v decreases with depth within the top 30 cm of sediment. Our study also found that K v varies spatially across geomorphological units, with strong variability in lower alluvial fan regions and moderate variability in alluvial and marine plains regions. In addition, the Gaussian model emerges as the most suitable for characterizing the spatial variability of K v . Longitudinally, significant variability occurs every 27 km to 30 km, aligning with variations in geomorphological units, sedimentary environments, and hydrological conditions. These findings provide critical data and theory for seepage fluxes estimation in similar watersheds. • The evolution pattern of vertical hydraulic conductivity at the basin scale was revealed. • The spatial variability characteristics of riverbed sediment vertical hydraulic conductivity was quantified. • The range of the variance was quantified in different directions.