Effects of streamflow and groundwater on hyporheic exchange in a sinuous gravel stream with pool-riffle sequences

Abstract

The hyporheic zone is the region surrounding a stream where stream water can actively move into, interact with and move out of. The resulting exchanges of water and materials, hyporheic exchanges (HE), are crucial to the physicochemical and biological processes in a stream. The HE in pool-riffle sequences are one of the most common forms and have received vast attention. Previous studies have mostly assumed the pool riffle sequences to be in straight streams even though in nature they tend to develop in meandering streams. Consequently, a comprehensive study of pool-riffle sequences is still missing. This study therefore aims to investigate the impacts of streamflow and groundwater flow on HE in sinuous pool-riffle gravel sequences. A scaled physical model is built in a laboratory flume where stream meanders and groundwater flow is incorporated. Tracer experiments are performed to quantify the influence of stream discharge and groundwater flow on the fluxes of HE. Experimental results reveal the quantitative relationships between HE and various hydraulic conditions in a sinuous gravel stream with pool-riffle sequences. Overall, the experiment setup of the study produces more realistic (i.e., meandering) but controlled conditions. The quantitative results help elucidate the basic processes that control the HE in natural streams, and benefit the development of stream restoration techniques.