The influence of microform bed roughness elements on flow and sediment transport in gravel bed rivers: A reply

<p>Recently, there has been an increasing attention on the environmental flow management for the maintenance of habitat diversity and ecosystem health of mountain gravel-bed rivers. More specifically, much interest has been paid to how inter-flood low flow can affect gravel-bed river morphodynamics during subsequent flood events. Such an effect is often termed as &#8220;stress history&#8221; effect. Previous research has found that antecedent conditioning flow can lead to an increase in the critical shear stress and a reduction in sediment transport rate during a subsequent flood. But how long this effect can last during the flood event has not been fully discussed. In this study, a series of flume experiments with various durations of conditioning flow are presented to study this problem. Results show that channel morphology adjusts significantly within the first 15 minutes of the conditioning flow, but becomes rather stable during the remainder of the conditioning flow. The implementation of conditioning flow can indeed lead to a reduction of sediment transport rate during the subsequent hydrograph, but such effect is limited only within a relatively short time at the beginning of the hydrograph. This indicates that bed reorganization during the conditioning phase, which induce the stress history effect, is likely to be erased with increasing intensity of flow and sediment transport during the subsequent flood event.</p>

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Effect of stress history on sediment transport and channel adjustment in graded gravel-bed rivers

10.5194/esurf-2020-67 ◽

2020 ◽

Author(s):

Chenge An ◽

Marwan A. Hassan ◽

Carles Ferrer-Boix ◽

Xudong Fu

Keyword(s):

Sediment Transport ◽

Critical Shear Stress ◽

Transport Rate ◽

Low Flow ◽

Flood Event ◽

Flume Experiments ◽

Stress History ◽

Gravel Bed ◽

Sediment Transport Rate ◽

Gravel Bed Rivers

Abstract. With the increasing attention on environmental flow management for the maintenance of habitat diversity and ecosystem health of mountain gravel-bed rivers, much interest has been paid to how inter-flood low flow can affect gravel-bed river morphodynamics during subsequent flood events. Previous research has found that antecedent conditioning flow can lead to an increase in the critical shear stress and a reduction in sediment transport rate during a subsequent flood. But how long this effect can last during the flood event has not been fully discussed. In this paper, a series of flume experiments with various durations of conditioning flow are presented to study this problem. Results show that channel morphology adjusts significantly within the first 15 minutes of the conditioning flow, but becomes rather stable during the remainder of the conditioning flow. The implementation of conditioning flow can indeed lead to a reduction of sediment transport rate during the subsequent hydrograph, but such effect is limited only within a relatively short time at the beginning of the hydrograph. This indicates that bed reorganization during the conditioning phase, which induce the stress history effect, is likely to be erased with increasing intensity of flow and sediment transport during the subsequent flood event.

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A 2D hydrodynamic-sedimentological model for gravel-bed rivers. Part I: theory and validation

Journal of Agricultural Engineering ◽

10.4081/jae.2013.263 ◽

2013 ◽

Vol 44 (2s) ◽

Author(s):

Gabriel Kaless ◽

Mario A. Lenzi ◽

Luca Mao

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Size Distribution ◽

Grain Size Distribution ◽

Gravel Bed ◽

Bed Elevation ◽

Shallow Water Flows ◽

Morphological Model ◽

Gravel Bed Rivers ◽

Transported Material

This paper presents a novel 2D-depth average model especially developed for gravel-bed rivers, named Lican-Leufú (Lican=pebble and Leufu=river, in Mapuche’s language, the native inhabitants of Central Patagonia, Argentina). The model consists of three components: a hydrodynamic, a sedimentological, and a morphological model. The flow of water is described by the depth-averaged Reynolds equations for unsteady, free-surface, shallow water flows. It includes the standard k-e model for turbulence closure. Sediment transport can be divided in different size classes (sand-gravel mixture) and the equilibrium approach is used for Exner’s equation. The amour layer is also included in the structure of the model and the surface grain size distribution is also allowed to evolve. The model simulates bank slides that enable channel widening. Models predictions were tested against a flume experiment where a static armour layer was developed under conditions of sediment starvations and general good agreements were found: the model predicted adequately the sediment transport, grain size of transported material, final armour grain size distribution and bed elevation.

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