Resistance of soils to concentrated flow erosion: A review

https://openresearch-repository.anu.edu.au/bitstream/1885/33581/2/01_McVicar_Spatially_distributing_monthly_2007.pdf

Spatially distributing monthly reference evapotranspiration and pan evaporation considering topographic influences

http://www.igsnrr.cas.cn/xwzx/jxlwtj/200607/P020090715579800622889.pdf

Change of soil physical properties under long-term natural vegetation restoration in the Loess Plateau of China

Effects of different vegetation restoration on soil water storage and water balance in the Chinese Loess Plateau

Rill erosion: Exploring the relationship between experiments, modelling and field observations

Quantification of soil detachment rates is necessary to establish a basic understanding of soil erosion processes and to develop fundamental-based erosion models. Many studies have been conducted on the detachment rates of disturbed soils, but very little has been done to quantify the rates of detachment for natural soil conditions. This study was conducted to evaluate the influence of flow discharge, slope gradient, flow velocity, shear stress, stream power, and unit stream power on detachment rates of natural, undisturbed, mixed mesic typical Udorthent soil. Flow rates ranged from 0.25 to 2.0 L s -1 and slope gradient ranged from 8.8 to 46.6%. This study was compared with a previous study that used disturbed soil prepared by static compression. The results indicated that the detachment rates of disturbed soil were 1 to 23 times greater than the ones of natural undisturbed soil. It was necessary to use natural undisturbed soil samples to simulate the detachment process and to evaluate the influence of hydraulic parameter on detachment rate. Along with flow rate increasing, detachment rate increased as a linear function. Detachment rate also increased with slope gradient, but the functional relationship between the two variables depended on flow rate. Stepwise regression analysis indicated that detachment rate could be well predicted by a power function of flow rate and slope gradient (R 2 = 0.96). Mean flow velocity was closely correlated to detachment rate (r 2 = 0.91). Flow detachment rate was better correlated to a power function of stream power (r 2 = 0.95) than to functions of either shear stress or unit stream power.

/pdf/detachment-of-undisturbed-soil-by-shallow-flow-1o8sec9k3q.pdf

Detachment of Undisturbed Soil by Shallow Flow

Precise estimation of sediment transport capacity (T c ) is critical to the development of physically based erosion models. Few data are available for estimating T c on steep slopes. The objectives of this study were to evaluate the effects of unit flow discharge (q), slope gradient (S), and mean flow velocity on T c in shallow flows and to investigate the relationship between T c and shear stress, stream power, and unit stream power on steep slopes using a 5-m-long and 0.4-m-wide nonerodible flume bed. Unit flow discharge ranged from 0.625 x 10- 3 to 5 x 10- 3 m 2 s ―1 and slope gradient from 8.8 to 46.6%. The diameter of the test riverbed sediment varied from 20 to 2000 μm, with a median diameter of 280 βm. The results showed that T c increased as a power function with discharge and slope gradient with a coefficient of Nash―Sutcliffe model efficiency (NSE) of 0.95. The influences of S on T c increased as S increased, with T c being slightly more sensitive to q than to S. The T c was well predicted by shear stress (NSE = 0.97) and stream power (NSE = 0.98) but less satisfactorily by unit stream power (NSE = 0.92) for the slope range of 8.8 to 46.6%. Mean flow velocity was also a good predictor of T c (NSE = 0.95). Mean flow velocity increased as q and S increased in this study. Overall, stream power seems to be the preferred predictor for estimating T c for steep slopes; however, the predictive relationships derived in this study need to be evaluated further in eroding beds using a range of soil materials under various slopes.

Sediment Transport and Soil Detachment on Steep Slopes: I. Transport Capacity Estimation

article i nfo Land use change has significant effects on soil properties and vegetation cover and thus probably affects soil detachment by overland flow. Few studies were conducted to evaluate the effect of restoration models on the soil detachment process in the Loess Plateau where a Grain for Green Project has been implemented in the past fourteen years. This study was performed to study the effects of vegetation restoration models on soil detachment by overland flow and soil resistance to rill erosion as reflected by rill erodibility and critical shear stress. The undisturbed soil samples were collected from five 37-year-restored lands of abandoned farmland, korshinsk peashrub land (Caragana korshinskill Kom.), black locust land (Robinia pseudoacacia Linn.), Chinese pine land (Pinus tabuliformis Carr.) and mixed forest land of amorpha and Chinese pine. The samples were subjected to flow scouring in a 4.0 m long by 0.35 m wide hydraulic flume under six different shear stresses ranging from 5.60 to 18.15 Pa. The results showed that the measured soil detachment capacities were affected significantly by the restoration models. The mean detachment capacity of cultivated farmland was 23.2 to 55.3 times greaterthan those of the restored or converted lands. Abandoned farmlandshowed maximum soil detach- ment capacity and was 1.02 to 2.29 times greater than the other four restored lands. Soil detachment capacity of the restored lands was significantly influenced by shear stress, cohesion, bulk density, total porosity and root mass density. Detachment capacities were negatively related to cohesion (p b 0.01) with linear function and root mass density (p b 0.05) with exponential function, but positively to total porosity (p b 0.01) with linear function. The rill erodibility would be negatively related to cohesion (p b 0.01) with power function. Besides, the low rill erodibility in the restored lands always had a low soil detachment capacity, while the critical shear stress in the restored lands varied non-monotonically with detachment capacity. The mixed forest land of amorpha and Chinese pine was considered as the best restoration model for its important role in reducing soil detachment capacity.

Soil detachment by overland flow under different vegetation restoration models in the Loess Plateau of China

A precise understanding of soil detachment rates is necessary to establish a basic understanding of soil erosion
and to develop a fundamentally based erosion model. This study was conducted to investigate the relationships between soil
detachment rates and flow discharge, slope gradient, flow depth, mean flow velocity, shear stress, unit stream power, and
stream power. A 5–m long  0.4–m wide hydraulic flume with constant artificial roughness upstream of and surrounding the
sample area was used. Flow discharge ranged from 0.25 to 2.0 L s –1 and slope gradient varied from 3.5% to 46.6%. The
experimental results indicated that detachment rates increased with both greater flow discharge and slope gradient.
Detachment rate was affected more by discharge than by slope gradient. The influence of slope gradient on detachment rate
was greater at high slopes. The effect of flow depth on soil detachment rate was also dependent on slope gradient. Stepwise
variable selection analyses indicated that detachment rate could be predicted by a power function of discharge and slope
gradient (R 2 = 0.97). Substituting flow depth for discharge gave a poorer prediction (R 2 = 0.92). Mean flow velocity was more
closely correlated to detachment than was any other hydraulic parameter (r 2 = 0.90). Flow detachment rates were better
correlated to a power function of stream power (r 2 = 0.89) than to functions of either shear stress or unit stream power. The
results of this study suggest that soil detachment by shallow flow is more closely related to flow energy than to shear stress.

Soil detachment by shallow flow

Measurements of temporal variations in soil detachability under different land uses are badly needed to develop new algorithms or evaluate the existing ones for temporal adjustment of soil detachability in continuous soil erosion models. Few studies have been conducted in the Loess Plateau to quantify temporal variations in detachment rate of runoff under different land uses. The objectives of this study were to investigate the temporal variations of soil detachment rate under different land uses and to further identify the potential factors causing the change in detachment rate in the Loess Plateau. Undisturbed soil samples were collected in the fields of arable land (millet, soybean, corn, and potato), grassland, shrub land, wasteland, and woodland and tested in a laboratory flume under a constant hydraulic condition. The measurements started in mid-April and ended in early October, 2006. The results showed that soil detachment rate of each land use fluctuated considerably over time. Distinctive temporal variation in detachment rate was found throughout the summer growing season of measurement in each land use. The maximum detachment rates of different land uses varied from 0·019 to 0·490 kg m–2 s–1 and the minimum detachment rates ranged from 0·004 to 0·092 kg m–2 s–1. Statistical analysis using a paired-samples t-test indicated that variations in soil detachment rate differed significantly at the 0·05 level between land uses in most cases. The major factors responsible for the temporal variation of soil detachment were tillage operations (such as planting, ploughing, weeding, harvesting), soil consolidation, and root growth. The influence of tillage operations on soil detachment depended on the degree of soil disturbance caused by the operations. The consolidation of the topsoil over time after tillage was reflected by increases in soil bulk density and soil cohesion. As soil bulk density and cohesion increased, detachment rate decreased. The impact of root density was inconclusive in this study. Further studies are needed to quantify the effects of root density on temporal variations of soil detachment. This work provides useful information for developing temporal adjustments to soil detachment rate in continuous soil erosion models in the Loess Plateau. Copyright © 2009 John Wiley & Sons, Ltd.

Guang-hui Zhang

Papers

Detachment of Undisturbed Soil by Shallow Flow

Sediment Transport and Soil Detachment on Steep Slopes: I. Transport Capacity Estimation

Soil detachment by overland flow under different vegetation restoration models in the Loess Plateau of China

Soil detachment by shallow flow

Temporal variation in soil detachment under different land uses in the Loess Plateau of China.