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2020 | Buch

Experimental Erosion

Theory and Practice of Soil Conservation Experiments

verfasst von: Prof. Xiangzhou Xu, Prof. Tongxin Zhu, Prof. Hongwu Zhang, Lu Gao

Verlag: Springer Singapore

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This book is the first to systematically explore experimental erosion by integrating theory, erosion observations, and conservation applications. Although numerous books have been published on soil erosion both in English and in Chinese, none has concentrated on experimental studies on the Loess Plateau of China, in an attempt to establish a new sub-discipline: experimental erosion.

One main objective of this book is to highlight monitoring and modeling methods for soil scientists who design and conduct experimental studies on soil loss. Another objective, and the most important one, is to make the results of these experiments more generally available. Accordingly, we have gathered and integrated a broad range of experimental results, both published and unpublished. In-depth discussions of the experimental data and new data processing methods are also included. The work covered here represents exemplary studies in the field of soil erosion and conservation, while the new methods and findings presented will provide practical guidance for controlling soil erosion. Hence the book offers a valuable resource for graduate students, soil erosion scientists and engineers, and soil and water conservationists.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Introduction
Abstract
An understanding of erosion processes is important for the design and operation of soil conservation projects, and study related to environmental and ecological issues. This collection of work develops new data sets and experimental methods to quantify the dynamics of soil loss that represent different stages in the development of soil functions. The application of the new data tests how simulation and observation can be coupled to guide beneficial intervention in soils in order to control soil erosion, especially that on the steep slope.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao

Theories and Methods for Soil Conservation Experiments

Frontmatter
Chapter 2. Similarity of Model Experiments
Abstract
A successful experiment with a physical model requires necessary conditions of similarity. This chapter presents an experimental method with a semi-scale physical model. Four criteria are mentioned here: similarities of watershed geometry, grain size and bare land, Froude number (Fr) for rainfall event, and soil erosion in the downscaled models. The efficacy of the proposed method was confirmed using these criteria in two different downscaled model experiments. Experimental results show that while the amount of soil loss in the small scale models was converted by multiplying the scale number, the amount was very close to that of the large scale model. Obviously, with a semi-scale physical model, the experiments are available to verify and predict the soil loss in a catchment with the check dam system on the Loess Plateau, China.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Chapter 3. A Conventional Experimental Technique: Rainfall Simulation
Abstract
Rainfall simulation is widely used for the experimental study on soil and water conservation. This chapter reviews the characteristics, application, and prospect of rainfall simulator. The rainfall simulators could be divided into two main groups: the non-pressurized rainfall simulators, including the thread droppers and the needle droppers, and the pressurized water rainfall simulators, including the spout and the sprayer. The former could be hardly found at present due to its drawback that the minimum size of drop produced is far larger and more even than most natural rainfall and the simulator could not easily generate rains with the similar energy to the natural one. Rainfall simulation halls with automatic operation and observation systems are booming in recent years, but the basic simulators will not be completely replaced in virtue of the cheap price and convenient manipulations.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Chapter 4. An Innovative Measurement Instrument: Topography Meter
Abstract
The measurement of failure mass is very difficult because gravity erosion usually occurs randomly and it combines with hydraulic erosion. Here, we present a novel structured-light 3D surface measuring apparatus, the topography meter, which could quantitatively measure the time-variable gravity erosion on the steep loess slopes. With the topography meter, a 3D geometric shape of the target surface could be digitally reconstructed, and then, the slope parameters, including the volume, projected area, and gradient distribution, could be obtained. By comparing the slope geometries in the moments before and after the erosion incident on the snapshot images at a particular time, we could obtain the volume of gravity erosion and many other erosion data. A series of calibration tests were conducted and the results showed that the accuracy of this technique was high and sufficient for exploring the mechanism of slope erosion.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Chapter 5. How to Conduct an Experiment in the Field: A Portable Laboratory
Abstract
Observation of the gravity erosion in the field with strong sunshine and wind poses a challenge. Here, a novel topography meter together with a movable tent addresses the challenge. With the topography meter, a 3D geometric shape of the target surface can be digitally reconstructed. Two methods can be used to obtain a relatively clear video, despite the extreme steepness of the slopes. One method is to rotate the laser source away from the slope to ensure that the camera sightline remains perpendicular to the laser plane. Another way is to move the camera farther away from the slope in which the measured volume of the slope needs to be corrected; this method will reduce the distortion of the image. In addition, the installation of tent poles with concrete columns helps to surmount the altitude difference on steep slopes. Results observed by the topography meter in real landslide experiments are rational and reliable.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao

Soil Conservation Experiments: Case Studies on the Loess Plateau, China

Frontmatter
Chapter 6. A Close Look of the Gravity Erosion on the Loess Plateau of China
Abstracts
Landslide plays an important role in landscape evolution, delivers huge amounts of sediment to rivers and seriously affects the structure and function of ecosystems and society. Here, a statistical analysis together with a field investigation was carried out on the Loess Plateau of China. Since the 1980s, 53 fatal landslides have occurred, causing 717 deaths. As the most important trigger, rainfall induced 40% of the catastrophic landslides, while other factors, i.e., human activities, freeze-thaw and earthquake, accounted for 36, 23 and 1%, respectively. Furthermore, the landslide frequency and death toll related to human activities were increasing as time went on. Landslide also plays an important role in sediment delivery, especially in the areas with steep terrain. In some catchments of the Loess Plateau, landslides contributed over 50% of the total sediment discharge. The result shows that landslide is a widespread geologic hazard in the rural area of the Loess Plateau, China.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Chapter 7. Effects of Conservation Practices on Soil, Water, and Nutrients
Abstract
To comprehensively assess the merits and demerits of the conservation practices is of great importance in further supervising the conservation strategy for the Loess Plateau. This chapter calculates the impact factors of conservation practices on soil, water, and nutrients during the period 1954–2004 in the Nanxiaohegou Catchment, a representative catchment on the Loess Plateau, China. Soil erosion and nutrient loss had been greatly mitigated through various conservation practices. About half of the total transported water and 94.8% of the total transported soil and nutrients had been locally retained in the selected catchment. The retention abilities of the characteristic conservation practices were in the following order: dam farmland > terrace farmland > forest land or grassland. Hence the check dam was the most appropriate conservation practice on the Loess Plateau. The conservation practices were more powerful in retaining sediment than in reducing runoff from the Loess Plateau.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Chapter 8. Sediment-Storage Effects of Check-Dam System in the Small Watershed
Abstract
The building of check-dams is one of the most effective measures for the conservation of soil and water on the Loess Plateau of China, and the hydro-sedimentologic balance is the most important factor influencing the relative stability of the check-dam systems. This means that soil and water in the small watersheds controlled by the check-dams will be absorbed internally, without the need of raising the height of the dams, if some given parameters have reached certain values. A runoff simulation experiment for a single check-dam and a rainfall simulation experiment for the whole check-dam system had been conducted to simulate the induced morphological changes affecting the stability of check dam systems. The results indicate that the main reasons causing the check-dam to show good relative stability are the enlargement of the dam-land area, the alleviation of erosion by the check-dam, and the auto-stabilizing mechanism of the gullies.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Chapter 9. Gravity Erosions on the Loess Gully Bank: Avalanche, Landslide, or Mudslide
Abstract
Gravity erosion is a dominant geomorphic process on the steep loess slopes. Here, we conducted rainfall simulation experiments to monitor occurrence and behavior of the mass failure on steep loess slopes. The results show that the quantity of soil loss caused by the avalanche and landslide was much more than that caused by the mudslide, and the avalanche was the most violent gravity erosion. As the slopes were eroded with five runs of rainfalls each at a duration of 48 mm, the total volume of avalanche, landslide, and mudslide were 150.9 × 103, 82.5 × 103, and 3.9 × 103 cm3/m, and accounted for 62, 36, and 2% of the total gravity erosion, respectively. Furthermore, the slope height and gradient had a remarkable positive correlation with the erosion amount. As a result, the avalanche and landslide, especially the former, played a crucial role in soil erosion on steep slope compacted by hand with loess.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Chapter 10. A Sensitivity Analysis on the Gravity Erosion on the Steep Loess Slope
Abstract
Gravity erosion is a dominant geomorphic process on the widespread steep loess slopes, yet it is not well understood due to the complexity of failure occurrence and behavior. This chapter conducted a series of laboratory experiments to test the stability of different slope geometries and rainfalls and then performed a sensitivity analysis. The following three types of gravity erosion were observed: landslide, avalanche, and mudslide. In an event of rainfall, various types of gravity erosion might emerge in the same period, and mass failures with the same mode and similar size often adjacently appeared. Climate-driven factors and topography triggers had prominent influences on gravity erosion. Whether for the total amount or the peak amount in an experiment, the largest sensitivity parameter on both landslides and mudslides was that of rainfall duration. The experimental results provide an insight into the pre-failure mechanisms and processes of steep loess slopes.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Chapter 11. Detecting Fingerprints of Gravity Erosion Drivers: A Laboratory Experiment
Abstract
The morphology of the failure scar has been a long-debated issue concerning the Loess Plateau of China, and the lack of normative data has hampered vital research in this area. In this chapter, a series of laboratory experiments were conducted to observe the failure geometries and volumes under rainfall simulations. The following six failure-scar types occurred: Tf, Cd, Cu, Ia, Ps, and Co. Tf, Cd, and Cu were the three major types of failure scars during the process of gravity erosion on a steep loess slope, and the scar Tf was the most significant. A relatively dangerous failure scar (Tf) might appear if the slope became steeper, or if the rainfall became more intensive. In addition, a long-duration storm could easily induce a large-volume failure with a Cu scar. The experimental results obtained here provide a morphogenic insight into the gravity-erosion control on a loess gully sidewall.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Chapter 12. Effects of Gravity Erosion on Particle Size Distribution of Suspended Sediment
Abstract
Gravity erosion generates an enormous volume of sediments on steep slopes throughout the world, yet its effect on the particle size distribution of suspended sediments (PSDSS) remains poorly understood. In this chapter, experiments were conducted in a field mobile laboratory in which mass movements were triggered on steep slopes under simulated rainfall. A suite of indexes such as median sediment size (d50), sediment heterogeneity (H), fractal dimension (D), and enrichment/dilution ratio (Red) were used to evaluate the effect of mass movement on PSDSS. Mass movements led to a drastic increase in the sediment concentration and the enrichment of fine particles, which developed into hyperconcentrated flows. \( R_{\text{ed}}{\text{s}} \) for clay, silt, and sand fractions were 13.9, 1.4, and 0.7 respectively. The d50, H, and D were significantly correlated with slope failures. The changes of PSDSS after mass movements reflected a combined complex effect of soil sources, erosion types, selective detachment, and deposition processes.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Chapter 13. Tunnel Flow and Erosion Processes in an Experimental Catchment
Abstract
Soil pipes and tunnels have been reported in a wide range of climatic conditions in the world, yet their hydrological and sediment processes have been much understudied in comparison with surface flows. In this chapter, storm flows and sediment processes were monitored at 6 tunnel systems in an experimental catchment in the Loess Plateau. The results indicate that all the tunnel flow was derived from overland flow entering via inlets. However, both flow discharges and sediment concentrations were highly erratic due to the instability of tunnel systems. Tunnels could be clogged by collapse inside, which reopened in subsequent events. An intensive storm could develop new inlet(s), which either joined the existing tunnel system or started a new one. Partial damming within the tunnel systems also frequently occurred. This chapter showed that at least 43% of water flows and 57% of sediments were routed via tunnels in the experimental catchment.
Xiangzhou Xu, Tongxin Zhu, Hongwu Zhang, Lu Gao
Backmatter
Metadaten
Titel
Experimental Erosion
verfasst von
Prof. Xiangzhou Xu
Prof. Tongxin Zhu
Prof. Hongwu Zhang
Lu Gao
Copyright-Jahr
2020
Verlag
Springer Singapore
Electronic ISBN
978-981-15-3801-8
Print ISBN
978-981-15-3800-1
DOI
https://doi.org/10.1007/978-981-15-3801-8