Influences of overlapped riparian groundwater mounds on interaction between surface water and groundwater

Abstract

A losing river usually produces riparian groundwater mounds. Knowledge of influences of the mound on riparian hydrological processes is still limited. To fill the gap, we measured the annual regime of riparian groundwater at a cross-section of a river channel in a semi-arid valley where the water transfer is running. Results show that the hydrologic processes were totally controlled by the water transfer. The river runoff was dominated by the transferred water. Regulation of the water transfer caused river stage fluctuations that were companied by hydrochemical variations of the river water. The water transfer enhanced infiltration into the riparian zone. Consequently, the river water and the riparian groundwater kept connection during the one-year observation. The annual recharge and the input of total dissolved solids (TDS) from the river to the riparian zone reached 195.8 m 3 and 125.0 kg, respectively. Furthermore, the Pearson's r between the river stage and riparian groundwater level was 0.98 at 2 m, 0.94 at 20 m, and 0.93 at 40 m (α = 0.01) from the riverside, respectively. The curved river produces the convergence of hydraulic gradients, which drives the overlap of groundwater mounds. The overlap is evidenced by anomalies in water level, hydrochemistry, and temperature of the riparian groundwater at the cross-section. When the river stage and adjacent groundwater level went down, the overlap locally reversed the hydraulic gradient to point to the river hindering the recharge from the river. Hence, the average daily recharge from the river decreased from 1.10 to 0.59 m 3 . The riparian groundwater discharged into the river after quick declines of the river stage. In total, 39.2 m 3 of riparian groundwater discharged into the river accounting for 20% of the annual recharge from the river. The impact of the hydrochemical variation of the river water on the riparian groundwater was also blocked due to the overlap. Also 20% of the TDS input was returned to the river. The overlap reduced the impact of the water transfer on the local environment.groundwater mound, hydrologic processes, interaction between surface water and groundwater, riparian zone, the Fen River, water transfer | INTRODUCTIONRiparian zone, the part of the watershed immediately adjacent to the stream channel, is considered as buffer zones and gateways of nutrients and pollutants in catchments for streams (Hester & Fox, 2020;Li et al., 2020). Hydrological processes in riparian zones play an important role in the controlling of hydrogeochemical (Veizaga

Mechanism controlling groundwater chemistry in the hyper-arid basin with intermittent river flow: insights from long-term observations (2001–2023) in the lower Heihe River, Northwest China

“…All of the three largest endorheic rivers in northwestern China, the Tarim River (Tao et al, 2011;Qian et al, 2024), Heihe River (Akiyama et al, 2007;Cheng et al, 2014;Yu et al, 2023) and Shiyang River (Ma et al, 2005;Huo et al, 2008;Fang et al, 2022), are suffering from water deficits and riparian ecosystem crisis (Li et al, 2018;Chen et al, 2022). In this context, surface water replenishment under ecological water conveyance (EWC) leads to a reduction in water table depth (WTD), thereby facilitating the exchange between lower salinity surface water and groundwater, which effectively diminishes groundwater salinity and improves groundwater quality (Tao et al, 2008;Yuan et al, 2022). A comprehensive understanding of the hydrological cycle and the evolution of associated water chemistry holds fundamental importance for effective water resource managements and ecological restoration in these endorheic river basins (Li et al, 2018;Guo et al, 2019).…”