UNDERSTANDING RIVER CORRIDOR CONNECTIVITY ACROSS THE CONTINENTAL UNITED STATES (Invited Presentation)

River channels and their surrounding environments continually exchange mass and energy along the river network. Understanding the mechanics, and in particular the magnitude and timing of this exchange, is critical for modeling and prediction and to sustainably manage water resources under present and future socio-economic and climatic conditions. In this work, we used the model Networks with EXchange and Subsurface Storage (NEXSS) to assess when and where different hydrologic exchange processes are active along rivers within the continental United States. In particular, we investigate the synchrony of exchange between river channels and their adjacent hyporheic zone and floodplains. Synchrony is expected to amplify the biogeochemical effects of river corridor connectivity, resulting in a dominant control for water quality at the local and watershed scales. Asynchrony, on the other hand, is expected to attenuate the effects of connectivity. Using a simple routing scheme, we translate NEXSS estimates of fluxes and residence times into a cumulative measure of river corridor connectivity at the watershed scale, differentiating the contributions of hyporheic zones and floodplains. We find that the relative role of these exchange subsystems changes seasonally, driven by the intra-seasonal variability of discharge. We also find that the interplay between exchange processes varies with location, typically characterized by asynchrony in low-order streams and synchrony in high-order rivers. Understanding the competing nature of exchange processes is critical to represent connectivity in physics-based models for water quality and to design, implement, and evaluate sustainable water management practices at the scale of the nation.