ANALYSIS OF NESTED HYPORHEIC FLOW PATHS USING ANALYTICAL SPECTRAL SOLUTIONS

The use of spectral solutions for the three-dimensional groundwater flow equation have been widely used in groundwater modeling because it provides a reliable and computationally efficient alternative to numerical models while providing detailed analysis of multiscale flow systems from large (e.g., regional flows cells) to small (e.g. hyporheic flow cells) scales. With the aim to estimate bedform-driven hyporheic exchange, this study uses analytical spectral solutions with a novel approach based on rigorous statistical analysis to detect dominant frequencies with predefined significance levels. We used (1) synthetic bedforms (e.g., ripples and dunes) and (2) a 10km natural river segment in the Columbia River to evaluate the performance of the spectral solutions with respect to state-of-art- numerical models. Our results show that spectral solutions provide a useful tool for preliminary and quick assessments in quantifying hyporheic exchange on small and large domains. In particular, the interpretation of hyporheic fluxes by means of spectral decompositions make them a useful tool to gain a mechanistic understanding about the effects of complex bathymetric variations in the evolution of exchange fluxes and residence times, which ultimately control both chemical and biochemical processes.