Hydraulic properties of concentrated flow of a bank gully in the dry‐hot valley region of southwest China

Abstract

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 (Fr) 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. Copyright © 2015 John Wiley & Sons, Ltd.

The impact of flow discharge on the hydraulic characteristics of headcut erosion processes in the gully region of the Loess Plateau

“…In terms of temporal variation, the Froude number was higher than 1 for the gully bed under each flow discharge but less than 1 for the catchment area at 60-180, 18-82, and 14-28 min, with Froude number values This result was attributed to the fact that no increasing trend was observed among flow velocity with increasing flow discharge; however, the runoff depth increased due to the well development gully, especially under relatively high flow discharge.The data analysis showed that the flow velocity in these periods were 0.91-1.12, 0.84-1.05, and 1.03-1.22 times the value of the mean flow velocity, while the runoff depth was 1.10-1.42, 0.72-1.2, 1.15-1.31 times the mean runoff depth, respectively. The reason for the discrepancy with this study may be that the flow discharge inSu et al (2015) was 1.8 m 3 hr −1 and the gully height was 0.7 m, while the gully bed was 2 m. The lower flow discharge and gully height decreased the flow energy. In contrast, F I G U R E 1 2 Flow energy consumption at gully head and at total plots under different flow discharges F I G U R E 1 3 Sediment discharge under different flow dischargesSu et al (2015) found that Froude number far exceeded 1 in the catchment area but was less than 1 in the gully beds under 1.8 m 3 hr −1 in the dry-hot valley region of China.…”

“…Once the rainfall was larger than the daily rainfall intensity threshold, headcut erosion was initiated. Therefore, an increase in runoff would accelerate the headcut erosion process (Bennett et al, 2000;Bennett & Casalí, 2001;Su et al, 2014Su et al, , 2015. Additionally, the runoff flushing capacity increases, and more energy is consumed to transport the soil particles.…”

“…Therefore, the responses of hydraulic characteristics to soil erosion have received considerable attention in the scientific literature worldwide. Some researchers have introduced flow energy, such as kinetic energy, potential energy, and flow energy consumption to illustrate headcut erosion mechanisms (Su et al, 2015;Zhang et al, 2016;Zhang, Xiong, et al, 2018). However, the object in these studies mainly focused on slope erosion or watersheds.…”

“…Similarly,Wei, Li, Li, & Shen (2009) andGong et al (2011) concluded that the concentrated flow was turbulent in the loess landscapes with an ephemeral gully. In contrast, F I G U R E 1 2 Flow energy consumption at gully head and at total plots under different flow discharges F I G U R E 1 3 Sediment discharge under different flow dischargesSu et al (2015) found that Froude number far exceeded 1 in the catchment area but was less than 1 in the gully beds under 1.8 m 3 hr −1 in the dry-hot valley region of China. Therefore, the influence of runoff depth on Froude number in the catchment area was more significant than the influence of flow velocity.…”

Influence of bare soil and cultivated land use types upstream of a bank gully on soil erosion rates and energy consumption for different gully erosion zones in the dry-hot valley region, Southwest China

“…Su et al (2014) investigated temporal variations in bank gully morphology and headcut erosion rates in response to a range of concentrated flows in this region. At a specified initial headcut height and water discharge rate, Su et al (2015) found spatiotemporal variations in hydraulic properties from a bare gully catchment down to a gully headcut as well as correlations between flow energy consumption (DE) and soil erosion rates. Distribution of and factors influencing vegetation within a downstream gully bed has also been ascertained by data taken at the Yuanmou Gully Erosion and Collapse Experimental Station ).…”