Empirical Equations to Predict the Characteristics of Hyporheic Exchange in a Pool-Riffle Sequence

The hyporheic zone is the saturated interstitial space surrounding a stream. Water actively moves into, through, and out of the hyporheic zone, resulting in hyporheic exchange (HE), which is crucial to the physicochemical and biological processes in these systems. The HE in pool-riffle sequences is one of the most common forms of HE and has received a vast amount of attention. This study aimed to derive empirical equations to predict the scale, median residence time (RT), and flux of HE in a single pool-riffle sequence by considering stream discharge, bedform geometry, streambed hydraulic conductivity, and groundwater flow. The resulting equations, which were derived using previously published data, allow quick approximations of the mean depth, median RT, and flux of HE in a single pool-riffle sequence. Therefore, these equations can be used to conveniently and efficiently generate insights into the physicochemical and biological processes, facilitating the prediction of water quality and the restoration of HE in stream rehabilitation. The overall framework of the derived equations is also generally applicable to considering HE with additional influential factors (e.g., stream width, sinuosity, bed slope, alluvial depth) and cases with more available data.