How persistent is bedform-driven hyporheic exchange to episodic river-aquifer disconnections?

Hyporheic zones are transitional interfaces connecting rivers and aquifers. These interfaces are often perceived as ubiquitous as long as water flows in the channel; however, their persistence strongly depends on the relative role of exchange drivers and modulators. Here, we assess the enduring nature of bedform-induced advective pumping (the driver) hyporheic exchange under diverse groundwater (the modulator) hydrologic conditions. We use a multi-physics framework to model the response of the exchange process to seasonal- and event-scale groundwater table fluctuations that result in episodic river-aquifer disconnections. Our findings suggest that when we account for the water table dynamics, the bedform-driven exchange occurs only under limited circumstances, characterized by minor river-groundwater head gradients. Furthermore, even minor groundwater drawdown conditions can obliterate the hyporheic zone. These results reveal the fragility of advective pumping hyporheic exchange and carry significant implications for understanding biogeochemical transformations along intermittent and ephemeral river corridors.