Rill erosion constitutes one of the mechanisms of soil loss by water on agricultural land. However, studies on hillslope rill erosion characteristics and its intrinsic mechanisms are still unclear. The objectives of this study were to investigate the impacts of rainfall intensity and slope gradient on hillslope rill erosion processes, rill flow hydraulic characteristics and dynamic mechanisms. A soil pan (10 m long, 1.5 m wide and 0.5 m deep and with an adjustable slope gradient of 0–30°) was subjected to rainfall simulation experiments under three rainfall intensities (50, 75 and 100 mm h −1 ) of representative erosive rainfall and three typical slope gradients (10, 15 and 20°) on the Loess Plateau of China. The results showed that rill erosion exhibited significant contributions to hillslope soil erosion, occupying 62.2–84.8% of hillslope soil loss. The equation between the rill erosion rate with rainfall intensity and slope gradient was generated, which indicated that the impacts of rainfall intensity on hillslope rill erosion were greater than those of slope gradient. For the experimental treatments, the mean headward erosion rates varied between 2.2 and 8.2 cm min −1 , and they increased with an increase in either rainfall intensity or slope gradient. Most rill flow belonged to turbulent and subcritical flow regimes. The critical shear stress, the critical stream power, and the critical unit stream power of rill occurrence were 0.986 Pa, 0.207 N m −1  s −1 , and 0.002 m s −1 , respectively. Additionally, hillslope rill erosion was sensitive to rill flow velocity and stream power. In a word, rainfall intensity and slope gradient exhibited important impacts on rill erosion processes and its hydrodynamic characteristics. Therefore, preventing rainfall erosion and weakening slope gradient effects through conservation tillage are useful for reduction of rill erosion at loessial hillslopes.

Impacts of rainfall intensity and slope gradient on rill erosion processes at loessial hillslope.

Runoff generation and soil loss from slopes have been studied for decades, but the relationships among runoff, soil loss and rill development are still not well understood. In this paper, rainfall simulation experiments were conducted in two neighbouring plots (scale: 1m by 5m) with four varying slopes (17.6%, 26.8%, 36.4% and 46.6%) and two rainfall intensities (90 and 120mmh(-1)) using two loess soils. Data on rill development were extracted from the digital elevation models by means of photogrammetry. The effects of rainfall intensity and slope gradient on runoff, soil loss and rill development were different for the two soils. The runoff and soil loss from the Anthrosol surface were generally higher than those from the Calcaric Cambisol surface. Higher rainfall intensity produced less runoff and more sediment for almost each treatment. With increasing slope gradient, the values of cumulative runoff and soil loss peaked, except for the treatments with 90mmh(-1) rainfall on the slopes with Anthrosol. With rainfall duration, runoff discharge decreased for Anthrosol and increased for Calcaric Cambisol for almost all the treatments. For both soils, sediment concentration was very high at the onset of rainfall and decreased quickly. Almost all the sediment concentrations increased on the 17.6% and 26.8% slopes and peaked on the 36.4% and 46.6% slopes. Sediment concentrations were higher on the Anthrosol slopes than on the Calcaric Cambisol slopes. At 90mmh(-1) rainfall intensity, increasingly denser rills appeared on the Anthrosol slope as the slope gradient increased, while only steep slopes (36.4% and 46.6%) developed rills for the Calcaric Cambisol soil. The contributions of rill erosion ranged from 36% to 62% of the cumulative soil losses for Anthrosol, while the maximum contribution of rill erosion to the cumulative soil loss was only 37.9% for Calcaric Cambisol. Copyright (c) 2014 John Wiley & Sons, Ltd.

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Effects of rainfall and slope on runoff, soil erosion and rill development: An experimental study using two loess soils

Soil microtopography is a property of critical importance in many earth surface processes but is often difficult to quantify. Advances in computer vision technologies have made image-based three-dimensional (3D) reconstruction or Structure-from-Motion (SfM) available to many scientists as a low cost alternative to laser-based systems such as terrestrial laser scanning (TLS). While the performance of SfM at acquiring soil surface microtopography has been extensively compared to that of TLS on bare surfaces, little is known about the impact of vegetation on reconstruction performance. This article evaluates the performance of SfM and TLS technologies at reconstructing soil microtopography on 6 m × 2 m erosion plots with vegetation cover ranging from 0% to 77%. Results show that soil surface occlusion by vegetation was more pronounced with TLS compared to SfM, a consequence of the single viewpoint laser scanning strategy adopted in this study. On the bare soil surface, elevation values estimated with SfM were within 5 mm of those from TLS although long distance deformations were observed with the former technology. As vegetation cover increased, agreement between SfM and TLS slightly degraded but was significantly affected beyond 53% of ground cover. Detailed semivariogram analysis on meter-square-scale surface patches showed that TLS and SfM surfaces were very similar even on highly vegetated plots but with fine scale details and the dynamic elevation range smoothed out with SfM. Errors in the TLS data were mainly caused by the distance measurement function of the instrument especially at the fringe of occlusion regions where the laser beam intersected foreground and background features simultaneously. From this study, we conclude that a realistic approach to digitizing soil surface microtopography in field conditions can be implemented by combining strengths of the image-based method (simplicity and effectiveness at reconstructing soil surface under sparse vegetation) with the high accuracy of TLS-like technologies. Copyright © 2015 John Wiley & Sons, Ltd.

Assessing the performance of structure-from-motion photogrammetry and terrestrial LiDAR for reconstructing soil surface microtopography of naturally vegetated plots

The plant ecosystems are particularly sensitive to climate change in arid and semi-arid regions. However, the responses of vegetation dynamics to climate change in Central Asia are still unclear. In this study, we used the normalized difference vegetation index (NDVI) data to analyze the spatial-temporal changes of vegetation and the correlation of vegetation and climatic variables over the period of 1982–2012 in Central Asia by using the empirical orthogonal function and least square methods. The results showed that the annual NDVI in Central Asia experienced a weak increasing trend overall during the study period. Specifically, the annual NDVI showed a significant increasing trend between1982 and 1994, and exhibited a decreasing trend since 1994. The regions where the annual NDVI decreased were mainly distributed in western Central Asia, which may be caused by the decreased precipitation. The NDVI exhibited a larger increasing trend in spring than in the other three seasons. In mountainous areas, the NDVI had a significant increasing trend at the annual and seasonal scales; further, the largest increasing trend of NDVI mainly appeared in the middle mountain belt (1,700–2,650 m asl). The annual NDVI was positively correlated with annual precipitation in Central Asia, and there was a weak negative correlation between annual NDVI and temperature. Moreover, a one-month time lag was found in the response of NDVI to temperature from June to September in Central Asia during 1982–2012.

Vegetation dynamics and its response to climate change in Central Asia

Post-fire sediment yields can be up to three orders of magnitude greater than sediment yields in unburned forests. Much of the research on post-fire erosion rates has been at small scales (100 m2 or less), and post-fire sediment delivery rates across spatial scales have not been quantified in detail. We developed relationships for post-fire bedload sediment delivery rates for spatial scales up to 117 ha using sediment yield data from six published studies and two recently established study sites. Sediment yields and sediment delivery ratios (SDRs; sediment delivered at the catchment scale divided by the sediment delivered from a plot nested within the catchment) were related to site factors including rainfall characteristics, area, length, and ground cover. Unit-area sediment yields significantly decreased with increasing area in five of the six sites. The annual SDRs ranged from 0.0089 to 1.15 and these were more closely related to the ratio of the plot lengths than the ratio of plot areas. The developed statistical relationships will help quantify post-fire sediment delivery rates across spatial scales in the interior western United States and develop process-based scaling relationships. Published in 2013. This article is a U.S. Government work and is in the public domain in the USA.

https://www.fs.fed.us/rm/pubs_journals/2014/rmrs_2014_wagenbrenner_j001.pdf

Post‐fire bedload sediment delivery across spatial scales in the interior western United States

A total of 15 rainfall simulation experiments were conducted in a 1 m by 2 m box varying slope (10, 20, 30%) and rainfall intensity (60, 90, 120 mm h−1) The experiments were performed to study how rill networks initiate and evolve over time under controlled conditions with regard to the treatment variables considered, and to allow for input in a computer simulation model Runoff and sediment yield samples were collected Digital elevation models were calculated by means of photogrammetry for several time steps of most experiments The soil used in the experiments was a basal till derived Cambisol typical for the Swiss Plateau While significant differences were found for sediment yield, runoff did not vary significantly with treatment combinations Increasing rainfall intensity had a larger effect on sediment yield than increasing slope Rill density and energy expenditure decreased with time, suggesting that energy expenditure was a useful parameter to describe the emergence of rill network at the laboratory scale Copyright © 2010 John Wiley & Sons, Ltd

Marcel Schulze

Papers

Rill development and soil erosion: a laboratory study of slope and rainfall intensity