Influence of point bar on solute transportation in hyporheic zone within riparian zone with stratified structure

This study investigated the effect of point bar on solute transport in the hyporheic zone within a riparian zone (HZRZ) which had a stratified structure. Using a two-way flow riparian zone model, ten experimental groups were analysed. Quantitative analysis was performed to investigate the effect of point bar submergence depth (h), riparian zone sediment (s), and surface flow velocity (u) on solute transport. The findings showed that point bars improve solute transport in both the upper section of the point bar and the section where point bar located, while inhibiting it in the lower section of the point bar. Moreover, increasing the submergence depth of the point bar resulted in higher rates and areas of solute transport. However, once the point bar was fully submerged, its effectiveness in promoting solute transport diminished. Additionally, the hyporheic zone within the riparian zone, with its stratified structure, significantly reduced the slow-speed transportation period, resulting in only one-third of the observed solute mass compared with homogeneous gravel conditions. Among the factors influencing solute transport, the submergence depth of the point bar had the highest impact, followed by the riparian zone sediment and surface flow velocity. This study advances the understanding of hyporheic exchange within riparian zone and provides a scientific basis for ecological restoration in riparian zone.