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Effect of tributary inflow on reservoir turbidity current

Yining Sun, Ji Li Orcid Logo, Zhixian Cao Orcid Logo, Alistair G. L. Borthwick, János Józsa

Environmental Fluid Mechanics

Swansea University Author: Ji Li Orcid Logo

  • Accepted Manuscript under embargo until: 16th April 2023

Abstract

Fluvial flows carrying high sediment loads may plunge into reservoirs to form turbidity currents. However, the effects of tributary inflows on reservoir turbidity currents have remained poorly understood to date. Here a 2D double layer-averaged model is used to investigate a series of laboratory-sca...

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Published in: Environmental Fluid Mechanics
ISSN: 1567-7419 1573-1510
Published: Springer Science and Business Media LLC 2022
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa59842
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Abstract: Fluvial flows carrying high sediment loads may plunge into reservoirs to form turbidity currents. However, the effects of tributary inflows on reservoir turbidity currents have remained poorly understood to date. Here a 2D double layer-averaged model is used to investigate a series of laboratory-scale numerical cases. By probing into the hydro-sediment-morphodynamic processes, we find that tributary location and inflow conditions have distinct effects on the formation and propagation of reservoir turbidity currents, and lead to complicated flow dynamics and bed deformation at the confluence. Two flow exchange patterns are generated at the confluence: turbidity current intrusion from the main channel into the tributary; and highly concentrated, sediment-laden flow plunging from the tributary into the turbidity current in the main channel. Tributary sediment-laden inflow may cause the stable plunge point to migrate downstream and is conducive to propagation of the turbidity current, whilst the opposite holds in the case of clear-water inflow from the tributary. Tributary inflow leads to a lower sediment f lushing efficiency as compared to its counterpart without a tributary. Yet a high sediment concentration in the tributary may reinforce turbidity current in the reservoir, thereby increasing sediment flushing efficiency. Around the confluence, the planar distributions of velocity and bed shear stress of the turbidity current resemble their counterparts in confluence flows carrying low sediment loads or clear water. Yet, the bed exhibits aggradation near the confluence due to the turbidity current, in contrast to pure scour in a river confluence with a low sediment load. Appropriate account of tributary effects is required in studies of reservoir turbidity currents, and for devising strategies for long-term maintenance of reservoir capacity.
Keywords: Reservoir; Turbidity current; Tributary; Sediment flushing efficiency; Double layer-averaged model
College: College of Engineering
Funders: This work has been funded by the National Natural Science Foundation of China under Grant No. 12072244.