Model-Based Analysis of the Effects of Rippled Bed Morphologies on Hyporheic Exchange

Abstract

Groundwater–surface water (GW-SW) exchange processes are important due to their critical role in controlling the transport of pollutants and ecologically related materials in rivers. In this paper, the surface water–groundwater coupling models of five wavy riverbed topographies were developed, and surface water velocity and pressure distribution under different wavy bed surface morphologies were studied. The upflows and downflows of sediment–water interface (SWI) were determined and quantified; in addition, the depth of hyporheic exchange and the locations of slow flow points were obtained. The obtained results showed that rippled bed morphologies disturbed the surface water flow field and separated adherent water flow at the water–sediment interface. The slope angle of water–slope of rippled beds was negatively correlated with the pressure of the water–sediment interface and positively correlated with flow velocity at the peak of the rippled bed. Upwelling and downwelling distributions basically depended on the geometry of the riverbed and did not change by changing the surface water velocity. The crest was a stable demarcation point between upflows and downflows, and the hyporheic exchange flux was negatively correlated with the angle of sloping slope. A stagnation zone existed in the hyporheic zone where both lateral and vertical flow velocity components approached zero, and its depth was similar to the depth of hyporheic zone. A lateral stagnation zone was located near the boundary of the reverse exchange zone in the hyporheic zone, and vertical stagnation zones were located on both sides of the maximum pressure of the water–sediment interface.