Hyporheic Exchange in a Meandering Pool-Riffle Stream

Abstract

Interactions among stream characteristics, hyporheic exchange (HE), and groundwater flow are a crucial control for physicochemical and biological reactions in hyporheic zone (HZ). Many previous studies solely investigated the HE induced by pool-riffle bedforms or meanders but few research studied the interactions between them despite this pair of morphology generally coexisting in natural streams. Adopting similar laboratory and numerical methods as Huang and Chui (2021), https://doi.org/10.1029/2020WR029182 whose pool-riffle streams were straight, this study adequately studied the impacts of hydraulic and morphologic factors on the HE in meandering pool-riffle streams and highlighted the mutual influence among various factors such as bedform amplitude and sinuosity. The results show that meanders significantly complicate the three-dimensional hyporheic flow paths and increase the flowrate and scale of HE. The HE flowrate increases linearly with discharge, bed slope, and sinuosity. The total HZ volume and maximum lateral and vertical extents of HZ generally increase with discharge. They also increase with bed slope and sinuosity but only up to a particular threshold, and they remain nearly constant or slightly decrease after exceeding the threshold. All HE characteristics exponentially decrease with both losing and gaining groundwater flow, and losing conditions have less significant effects on the HE compared with gaining conditions. The HE in stream bank can be larger than that in streambed, and the former is generally more influenced by discharge and sinuosity than the latter. Effects of bedform amplitude on HE exhibit very complex patterns due to the mutual influence of key factors.