MULTISCALE STREAMBED TOPOGRAPHY CONTROLS ON HYPORHEIC ZONE DEVELOPMENT ALONG RIVER CORRIDORS

Owing to the important role played by the hyporheic zone in the transformation and attenuation of dissolved nutrients and contaminants in streams via vertical exchange with groundwater, the hyporheic zone has received great attention in recent decades. However, studies on the hyporheic zone have been largely limited to the pore and reach scales. This present study, therefore, aims to computationally assess the hyporheic zone processes on a regional scale by assessing the influence of multiscale streambed topography on hyporheic zone development along river corridors. COMSOL multiphysics was used to simulate the influence of different streambed topography conditions on the evolution of hyporheic zones and therefore provide insight on the potentials of hyporheic zone processes and their implications on biological transformations such as nitrification and denitrification, which are important processes in the natural attenuation of contaminants in stream water. The streambed topography was varied using parameters such as regional slope, slope curvature factor, pool-riffle amplitude and frequency, and stream stage. Results show that the regional slope has a very strong control on the degree of curvature of the streambed. However, the pool-riffle amplitude played a major role in controlling the extent of hyporheic zone development and exchange along river corridors. Although the stream stage showed some influence on hyporheic zone development along river corridors, the frequency and amplitude of pool-riffle sequence showed more dominance in controlling the development of hyporheic zones along river corridors. By implication, a stream regardless of its steepness experiences more hyporheic exchange when the streambed is configured with a deep and high frequency pool-riffle, and perhaps promotes adequate biological transformation to allow efficient contaminant attenuation of the stream water.