Semianalytical analysis of hyporheic flow induced by alternate bars

Abstract

[1] We investigate the effects of alternate bar morphology on the hyporheic flow in gravel bed rivers. Our goal is to investigate the relations between residence time distribution of a conservative tracer and the parameters controlling bed form morphology. We assume homogeneous, isotropic or anisotropic hydraulic properties of the streambed sediment and constant flow regime in equilibrium with the bed form, which is considered fixed because its formation timescale is much longer than that of the subsurface flow. Under these assumptions, we solve the in-stream and hyporheic flow fields analytically in a three-dimensional domain. We approximate the former with the shallow water equations and model the latter as a Darcian flow. The two systems are linked through the hydraulic head distribution, which is predicted at the streambed by the surface model and applied as a boundary condition to the hyporheic flow model. We solve the solute transport equation in the hyporheic zone for a conservative tracer by means of particle tracking. Our model predicts that the mean value and variance of the hyporheic residence time depend on the alternate bar amplitude at equilibrium. This result is found to be applicable also to discharges that are lower (70% in our simulations) than the formative and submerge the bars entirely. Moreover, our analysis shows that 95% of the hyporheic flow is confined in a near-bed layer, whose depth is about the width of the channel and shallows from low to steep gradient streams. This causes the hyporheic mean residence time to reach a threshold when the alluvial depth is deeper than the channel width. Our results also show that as the stream slope increases, the streamlines compact near to the streambed, thereby reducing the mean residence time and its variance. Finally, we observe that the hyporheic residence time of pulse injections of passive solutes is lognormally distributed, with the mean value depending in a simple manner on the amplitude of the alternate bars.

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

“…Bedform-induced hyporheic exchanges can be viewed as longitudinally 2-D vertical processes. Similar 2-D horizontal processes also occur in single or alternating unit bars (Burkholder et al, 2008;Cardenas, 2009a;Deforet et al, 2009;Derx et al, 2010;Marzadri et al, 2010;Shope et al, 2012) or bedform discontinuities (Hester and Doyle, 2008).…”

“…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. Ultimately a very fine scale process (∼ cm-dm), due to the in-stream nonhydrostatic flow induced by bedform microtopography (Fig.…”

Hydraulic Parameters and Morphometric Variables Interactions in Bedrock Channel

“…Change in channel forms are too slow to study in lifetime of a researcher. Yet bedrock channels play a great role in the scene of world ecosystem (Gurnell et al 2001, Marzadri et al 2010, Mosselman 2012, Nikora and Roy 2012. Bedrock channels supplies alluvium that forms substrate for the alluvial channel.…”

Scaling down hyporheic exchange flows: from catchments to reaches

“…Step-pool morphology behaves differently than pool-riffle and dune-like bedform (Storey et al, 2003;Tonina and Buffington, 2007;Marzadri et al, 2010;Hassan et al, 2015) 15 because the depth of hyporheic exchange increases with channel slope and deeper vertical exchanges develops at high slope.…”