Hydraulic properties of concentrated flow of a bank gully

What is it about?

To quantify spatiotemporal variation in hydraulic properties of bank gully concentrated flow, a series of scour experiments were run under water discharge rates ranging from 30 to 120 L min-1. Concentrated flows were found to be turbulent and supercritical in the upstream catchment area and downstream gully beds. As discharge increased, values of the soil erosion rate, Reynolds number (Re), shear stress, stream power, and flow energy consumption (ΔE) increased while values of the Froude number ( ) and the Darcy–Weisbach friction factor (resistance f) did not. With the exception of gully headcut collapse under discharge rates of 60, 90, and 120 L min-1, a declining power function trend (P < 0.05) in the soil erosion rate developed in the upstream catchment area, headcuts, and downstream gully beds. However, increasing trends were observed in temporal variations of hydraulic properties for downstream gully beds and the upstream catchment area. Despite significant differences in temporal variation between the soil erosion rate and hydraulic property values, relative steady state conditions of the soil erosion rate and ΔE were attained following an initial period of adjustment in the upstream catchment area, headcuts, and downstream gully beds under different discharge rates. A logarithmic growth of flow energy consumption per unit soil loss (ΔEu) was observed in bank gullies and the upstream catchment area as the experiment progressed, further illustrating the actual reason behind the discrepancy in temporal variation between soil erosion rates and ΔE. Results demonstrate that ΔE can be used to estimate headcut erosion soil loss, but further quantitative studies are required to quantify coupling effects between hydraulic properties and vertical variation in soil mechanical properties on temporal variation for bank gully soil erosion rates.

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Photo by Jim Witkowski on Unsplash

Photo by Jim Witkowski on Unsplash

Why is it important?

The objective of this study were to construct field-scale gullies in an in-situ channel to (1) examine the differences in temporal variation of hydrodynamic properties in response to a range of overland flow between gully heads and upstream areas (2) evaluate a prediction technology of headward erosion in bank gullies. Gully erosion is one kind of soil degradation phenomena in a wide variety of environments around the world, yet little attention has been paid to the hydrodynamic properties of the concentrated flow in the process of gully headward erosion. Additionally, in Dry-hot valley region of southwest China, gully erosion processes have not been well documented.

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