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| Titel |
Effect of Streambed Roughness and Topography on the Solute Transport and Hyporheic Exchanges: Laboratory Experiments |
| VerfasserIn |
Xiaobing Chen, Jian Zhao, Li Chen |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076854
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| Zusammenfassung |
| Hyporheic zones are critical for maintaining river ecosystem as they provide hyporheic and
riparian organisms critical solutes, including nutrients and dissolved gases from bedforms to
watershed scales. Among the hyporheic driving factors, the streambed topogaraphy is
considered as a significant driving factor for hydraulic process in hyporheic zone that has
been well documented in the past few decades. Previous research has implied that the rough
streambed impact the flow resistance and continuously affect the hydraulic gradient between
the river and the streambed. Recent research works focused more on the realistic pressure
distribution along the bedform interface (eg. triangular-shaped sand dunes) on a macro level
scale, while only few works related to the hyporheic exchanges induced by pore size
scaled topography. How and to what extent that pore size scaled bedform would
contribute to the total hyporheic discharge is still unclear. Indeed, the mesoscopic
uneven topography can disturb the flow regime that near the water-sand interface, for
example, it brings turbulent eddies and fluctuating pressure distribution along a
rough gravel bed. In our study, a set of flume experiments were setup to examine the
pore size roughness impacts on the solute transport and hyporheic exchanges in
surface-subsurface system. Six kinds of riverbed sediments with median diameter range from
1.1 mm to 50.2 mm were chosen for comparative analyses. Also, three kinds of
triangular shaped bedforms represented by the ratio α (=δ/λ, δ is the amplitude
and λ is the wavelength) with value of 0.125, 0.17 and 0.25 were considered as
the macro-topography driver variation in our experiments. Our tests revealed that
under a flat riverbed condition, the vertical diffusion is the main factor for the solute
transport in hyporheic zone, however, the hyporheic exchange rate (represented by the
decrease rate in concentration of surface water) is significantly enhanced as the growth
of gravel grain size. Results show that the hyporheic exchanges that attribute to
pore size roughness is relatively larger under a smaller δ, and less important as
macro-topography determine the exchange process. Results also show that the contribution in
hyporheic exchanges that induced by pore size topography is proportional to Re(=vd/ν). |
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