Clogging model of hyporheic exchange based on coupled lattice Boltzmann discrete element simulations

The hyporheic exchange between the surface water and the underground water is considered a significant process in the natural water cycle system. Some sediment particles in the riverbed can be carried to the exchange channel under the stream effect. Over time, these particles accumulate on the channel can decrease the exchange efficiency of water resources, and induce clogs. The clogging problem of the exchange channel may further induce various geological and environmental disasters such as the shrinkage of lakes and desertification.

To detail the clogging mechanism in the exchange channel, we simulated the exchange clogging process on the exchange channel based on a coupled lattice Boltzmann method (LBM) and discrete element method (DEM). The results indicated particles could form an arch structure clogging the channel orifice. The formation of the clogging arch prevented the discharge of soil particles and greatly decreased the fluid velocity. Notably, the fluid velocity distribution around the orifice is in a certain shape according to the velocity of the LBM cells—the size of the shape regularly changes with the distance to the channel orifice. The variation of the average fluid velocity in the orifice first increases to a peak (about 0.497 cm/s) in the initial time and then decreases to an approximate value after clogging (about 0.037 cm/s). The maximum velocity is almost thirteen times the minimum, indicating that the clogging effect can reduce the water velocity of hyporheic exchange by more than one order of magnitude. In addition, it was found that the soil skeleton was necessary for forming clogs in polydisperse particle systems by analyzing the clogging arch-forming process. The sediment particles in different scales have different effects on the clogging arch. The large particles in the sediments are closely related to the formation of the soil skeleton. The fine particles were involved in the filling and enhancing of the soil skeleton.

Based on our simulation analysis, an explanation for the clogging formation under microscopic conditions was proposed, leading to a detailed description of the exchange clogging in the hyporheic exchange channel. In addition, some mechanism statements to better understand the exchange phenomenon in the water cycling ecosystem are also provided.