Coupled 3-D stream flow and hyporheic flow model under varying stream and ambient groundwater flow conditions in a pool-riffle system

Abstract

[1] Exchange of water and solutes across the stream-sediment interface is an important control for biogeochemical transformations in the hyporheic zone (HZ). In this paper, we investigate the interplay between turbulent stream flow and HZ flow in pool-riffle streams under various ambient groundwater flow conditions. Streambed pressures, derived from a computational fluid dynamics (CFD) model, are assigned at the top of the groundwater model, and fluxes at the bottom of the groundwater model domain represent losing and gaining conditions. Simulations for different Reynolds numbers (Re) and pool-riffle morphologies are performed. Results show increasing hyporheic exchange flows (m 3 /d) for larger Re and a concurrent decrease in residence time (RT). Losing and gaining conditions were found to significantly affect the hyporheic flow field and diminish its spatial extent as well as rates of hyporheic exchange flow. The fraction of stream water circulating through the hyporheic zone is in the range of 1 Â 10 À5 to 1 Â 10 À6 per meter stream length, decreasing with increasing discharge. Complex distributions of pressure across the streambed cause significant lateral hyporheic flow components with a mean lateral travel distance of 20% of the longitudinal flow paths length. We found that the relationship between pool-riffle height and hyporheic exchange flow is characterized by a threshold in pool-riffle amplitude, beyond which hyporheic exchange flow becomes independent of riffle height. Hyporheic residence time distributions (RTD) are log-normally distributed with medians ranging between 0.7 and 19 h.

Continental hydrosystem modelling: the concept of nested stream–aquifer interfaces

“…Finally, the longitudinal morphology of the river and the topography of the riverbed, consisting of a pluri-metric succession of pools and riffles (Fig. 1e), also impact the stream-aquifer exchanges (Crispell and Endreny, 2009;Frei et al, 2010;Gooseff et al, 2006;Harvey and Bencala, 1993;Kasahara and Hill, 2006;Käser et al, 2013;Maier and Howard, 2011;Tonina and Buffington, 2007), until a threshold of streambed amplitudes is reached (Trauth et al, 2013). Likewise, the depth of the alluvial aquifer (Koch et al, 2011;Marzadri et al, 2010;Whiting and Pomeranets, 1997), and the river hydraulic regime (Cardenas and Wilson, 2007a;Munz et al, 2011;Saenger et al, 2005) influence stream-aquifer exchanges.…”

“…Due to the sequence, stream-aquifer exchanges seem to increase with the amplitude of the streambed oscillations, until a threshold is reached (Trauth et al, 2013). Also, combined streambed oscillating frequencies may increase the intensity of the exchanges in a complex way (Käser et al, 2013).…”

Impact of watershed topography on hyporheic exchange

“…However, the role of the hyporheic zone in this interaction has not been examined in detail [33,34,35,36,37]. Conversely, some modelling and experimental approaches have been developed specifically to investigate the impact of large-scale riveraquifer interactions on the main properties of local exchange at various scales 75 [28, 29,31,38].…”

TESSIN VISLab—laboratory for scientific visualization

“…6). Within that area a number of intensive test sites have been selected, ranging in size from a small area of about one hectare, concerned with assessment of water balance in a forested region, to the complete catchment of one of the Bode's tributaries with a size of over 450 km 2 where hydrological processes in the stream as well as in the hyporheic zone are investigated (Schmidt et al 2012;Trauth et al 2013) as shown in Fig. 7.…”