Spatiotemporal changes in flow hydraulic characteristics and soil loss during gully headcut erosion under controlled conditions

Mingming Guo,Tianchao Wang,Wenlong Wang,Lanqian Feng,Qianhua Shi,Man Zhao,Hongliang Kang,Zhuoxin Chen

doi:10.5194/hess-25-4473-2021

Abstract

Abstract. The spatiotemporal changes in flow hydraulics and energy consumption and their associated soil erosion remain unclear during gully headcut retreat. A simulated scouring experiment was conducted on five headcut plots consisting of upstream area (UA), gully headwall (GH), and gully bed (GB) to elucidate the spatiotemporal changes in flow hydraulic, energy consumption, and soil loss during headcut erosion. The flow velocity at the brink of a headcut increased as a power function of time, whereas the jet velocity entry to the plunge pool and jet shear stress either logarithmically or linearly decreased over time. The jet properties were significantly affected by upstream flow discharge. The Reynolds number, runoff shear stress, and stream power of UA and GB increased as logarithmic or power functions of time, but the Froude number decreased logarithmically over time. The Reynolds number, shear stress, and stream power decreased by 56.0 %, 63.8 %, and 55.9 %, respectively, but the Froude number increased by 7.9 % when flow dropped from UA to GB. The accumulated energy consumption of UA, GH, and GB positions linearly increased with time. In total, 91.12 %–99.90 % of total flow energy was consumed during headcut erosion, of which the gully head accounted for 77.7 % of total energy dissipation, followed by UA (18.3 %), and GB (4.0 %). The soil loss rate of the “UA-GH-GB” system initially rose and then gradually declined and levelled off. The soil loss of UA and GH decreased logarithmically over time, whereas the GB was mainly characterized by sediment deposition. The proportion of soil loss at UA and GH is 11.5 % and 88.5 %, respectively, of which the proportion of deposited sediment on GB reached 3.8 %. The change in soil loss of UA, GH, and GB was significantly affected by flow hydraulic and jet properties. The critical energy consumption initiating soil erosion of UA, GH, and GB is 1.62, 5.79, and 1.64 J s−1, respectively. These results are helpful for deepening the understanding of gully erosion process and hydrodynamic mechanisms and can also provide a scientific basis for the construction of gully erosion model and the design of gully erosion prevention measures.

Highlights

Erosion is a typical soil erosion process whereby concentrated runoff from an upstream drainage area recurs in a channel and erodes soil from the area through which runoff passes to considerable depth (Poesen et al, 2003; Zhu, 2012)
This study investigated the spatiotemporal changes in flow hydraulics, energy consumption, and soil loss during headcut erosion based on a series of scouring experiments of gully headcut erosion
The flow was supercritical on upstream area (UA) but subcritical on gully bed (GB), and the turbulent degree was enhanced by the increasing inflow discharge

Summary

Introduction

Erosion is a typical soil erosion process whereby concentrated runoff from an upstream drainage area recurs in a channel and erodes soil from the area through which runoff passes to considerable depth (Poesen et al, 2003; Zhu, 2012). Poesen et al (2003) reported that soil loss amount caused by gully erosion accounts for 10 %–94 % of total soil loss amount based on the collected data from published articles. M. Guo et al.: Spatiotemporal changes in flow hydraulic characteristics over, gully erosion can severely damage infrastructure, enhance the terrain fragmentation, and cause ecosystem instability, land degradation, and compromise food safety J. Zhang et al, 2018; Hosseinalizadeh et al, 2019; Arabameri et al, 2020; Bogale et al, 2020; Belayneh et al, 2020; Wen et al, 2020)

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