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Abstract Many water quality and ecosystem functions performed by streams occur in the benthic biolayer, the biologically active upper (~5 cm) layer of the streambed. Solute transport through the benthic biolayer is facilitated by bedform pumping, a physical process in which dynamic and static pressure variations over the surface of stationary bedforms (e.g., ripples and dunes) drive flow across the sediment‐water interface. In this paper we derive two predictive modeling frameworks, one advective and the other diffusive, for solute transport through the benthic biolayer by bedform pumping. Both frameworks closely reproduce patterns and rates of bedform pumping previously measured in the laboratory, provided that the diffusion model's dispersion coefficient declines exponentially with depth. They are also functionally equivalent, such that parameter sets inferred from the 2D advective model can be applied to the 1D diffusive model, and vice versa. The functional equivalence and complementary strengths of these two models expand the range of questions that can be answered, for example, by adopting the 2D advective model to study the effects of geomorphic processes (such as bedform adjustments to land use change) on flow‐dependent processes and the 1D diffusive model to study problems where multiple transport mechanisms combine (such as bedform pumping and turbulent diffusion). By unifying 2D advective and 1D diffusive descriptions of bedform pumping, our analytical results provide a straightforward and computationally efficient approach for predicting, and better understanding, solute transport in the benthic biolayer of streams and coastal sediments.
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The evolution of snow bedforms in the Colorado Front Range and the processes that shape them
Abstract. When wind blows over dry snow, the snow surface self-organizesinto bedforms such as dunes, ripples, snow waves, and sastrugi. Thesebedforms govern the interaction between wind, heat, and the snowpack, butthus far they have attracted few scientific studies.We present the first time-lapse documentation of snow bedform movement and evolution, as part of a series of detailed observations of snow bedform movement in the Colorado Front Range.We show examples of the movement of snow ripples, snow waves, barchan dunes,snow steps, and sastrugi. We also introduce a previously undocumentedbedform: the stealth dune. These observations show that (1) snow dunesaccelerate minute-by-minute in response to gusts, (2) sastrugi and snow stepspresent steep edges to the wind and migrate downwind as those edges erode,(3) snow waves and dunes deposit layers of cohesive snow in their wake, and(4) bedforms evolve along complex cyclic trajectories. These observationsprovide the basis for new conceptual models of bedform evolution, based onthe relative fluxes of snowfall, aeolian transport, erosion, and snowsintering across and into the surface. We find that many snow bedforms aregenerated by complex interactions between these processes. The prototypicalexample is the snow wave, in which deposition, sintering, and erosion occurin transverse stripes across the snowscape.
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- Award ID(s):
- 1637686
- PAR ID:
- 10126840
- Date Published:
- Journal Name:
- The Cryosphere
- Volume:
- 13
- Issue:
- 4
- ISSN:
- 1994-0424
- Page Range / eLocation ID:
- 1267 to 1281
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/tc-13-1267-2019
