The Fragility of Bedform-Induced Hyporheic Zones: Exploring Impacts of Dynamic Groundwater Table Fluctuations

Hyporheic zones are commonly regarded as resilient and enduring interfaces between groundwater and surface water in river corridors. In particular, bedform-induced advective pumping hyporheic exchange (bedform-induced exchange) is often perceived as a relatively persistent mechanism in natural river systems driving water, solutes, and energy exchanges between the channel and its surrounding streambed sediments. Numerous studies have been based on this presumption. To evaluate the persistence of hyporheic zones under varying hydrologic conditions, we use a multi-physics framework to model advective pumping bedform-induced hyporheic exchange in response to a series of seasonal- and event-scale groundwater table fluctuation scenarios, which lead to episodic river-aquifer disconnections and reconnections. Our results suggest that hyporheic exchange is not as ubiquitous as generally assumed. Instead, the bedform-induced hyporheic exchange is restricted to a narrow range of conditions characterized by minor river-groundwater head differences, is intermittent, and can be easily obliterated by minor losing groundwater conditions. These findings shed light on the fragility of bedform-induced hyporheic exchange and have important implications for biogeochemical transformations along river corridors.