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

Abstract

AbstractA 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 m3 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 m3. The riparian groundwater discharged into the river after quick declines of the river stage. In total, 39.2 m3 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.