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Exploring the influence of channel complexity and discharge on transient storage and hyporheic exchange in stream systems: insights from multiple logjams and channels

Gambill, Ian
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Abstract
To date, research on hyporheic exchange has been largely conducted in artificial or simple natural systems. Here, we explore how a complex stream system with multiple logjams and multiple channels drives hyporheic exchange flows, and how these vary with discharge at a site in the Front Range of Colorado, USA. During three tracer tests conducted from baseflow to near-peak snowmelt, we collected instream fluid conductivity measurements and conducted electrical resistivity surveys to characterize tracer movement and retention given the presence of logjams and a changing channel morphology. Breakthrough curve analysis and electrical resistivity inversions revealed that as discharge increased, channel complexity and flowpath distribution increased, leading to a higher variability in solute transport processes thereby increasing hyporheic exchange flow in our experimental reaches. Additionally, breakthrough curve analysis and electrical resistivity inversions showed that the reach with multiple logjams exhibited greater surface and subsurface transient storage, including higher hyporheic exchange flows, compared to the reach with a single logjam. This study is one of the first to characterize hyporheic exchange flows in a complex stream system with multiple logjams and multiple channels and highlights the importance of the presence of logjams and their influence on overall stream function.
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