The effects of tillage induced surface roughness,slope and discharge rate on soil detachment by concentrated flow: An experimental study     

Jiaqian Sun  Naichang Zhang  Mingxin Shi  Yanbin Zhai  Faqi Wu 《水文研究》2021,35(6):e14261

Soil erosion in sloping cropland is a key water and soil conservation issue in the Loess Plateau region, China. How surface roughness influences soil detachment remains unclear due to the inconsistent results obtained from existing studies. The objectives of the present study were to evaluate the effects of tillage practices on soil detachment rate in sloping cropland and establish an accurate empirical model for the prediction of soil detachment rates. A series of movable bed experiments were conducted on sloping surfaces under three different tillage practices (manual dibbling, manual hoeing, and contour drilling), with a smooth surface (non-tillage) as a control. The research indicated that soil detachment rate significantly increased with roughness (p < 0.05) since the average soil detachment rate was the highest under the contour drilling treatment (6.762 g m⁻² s⁻¹), followed by manual hoeing (4.180 g m⁻² s⁻¹), and manual dibbling (3.334 g m⁻² s⁻¹); the lowest detachment rate was observed under the non-tillage treatment (3.214 g m⁻² s⁻¹). Slope gradient and unit discharge rate were positively correlated with soil detachment rate and proved to be more influential than soil surface roughness. Four composite hydraulic parameters were introduced to estimate soil detachment rate on tilled surfaces. Regression analyses revealed that stream power was the most effective predictor of soil detachment rate compared with unit length shear force, shear stress, and unit stream power. By integrating surface roughness as a variable, the detachment rate could be accurately described as a nonlinear function of stream power and surface roughness. The results of the present study indicate that tillage practice could influence soil loss on sloping cropland, considering the higher soil detachment rates under all tillage practices tested compared with non-tillage. The results are attributed mainly to concentrated flow caused by the high water storage levels on tilled surfaces, which could damage surface microtopography and, subsequently, the development of headcuts.  相似文献   

滇东北山区坡耕地土壤侵蚀的水土保持措施因子   总被引：9，自引：2，他引：7  

杨子生 《山地学报》1999,17(Z1):2

通过对滇东北山区坡耕地５种主要水土保持措施———等高带状耕作、地埂、生物防冲带－绿肥、生物防冲带－苹果、水平梯地（梯田）对土壤流失量的控制作用建立试验小区并进行连续３年实测,得到各种水土保持措施的Ｐ值,为建立坡耕地水土流失方程、进行土壤侵蚀预测预报、制定坡耕地水土保持措施奠定了可靠的基础。  相似文献   

陕甘宁盆地姬塬地区三叠系延长组三角洲前缘的微相组合及特征   总被引：29，自引：0，他引：29  

王峰  王多云  高明书  姚永朝  王志坤  李树同  秦红 《沉积学报》2005,23(2):218-224

以陕甘宁盆地姬塬地区晚三叠系延长统为例,将该区的三角洲前缘划分为“台型前缘”和“坡型前缘”两部分,其识别标志是以水下分流河道、复合河口坝(坝上河)和河口坝三种主要沉积微相为主导的多种微相的不同组合。文中对三角洲前缘中的沉积微相组合进行了精细划分和描述,例如,将水下分流河道划分为截削式和叠加式2种,将河口坝划分为完整式和复合式两大类,其中复合式河口坝(坝上河)还可划分为下残坝上河、完整坝上河和上残坝上河三种亚类型。这种对三角洲前缘的详细解释以及对其沉积微相的精细描述有助于优质储层的鉴别和分布预测,对油藏开发中的细分流动单元也有所帮助。  相似文献   

Floating pontoon breakwaters   总被引：1，自引：0，他引：1  

A. N. Williams  H. S. Lee  Z. Huang 《Ocean Engineering》2000,27(3):3634

The hydrodynamic properties of a pair of long floating pontoon breakwaters of rectangular section are investigated theoretically. The structures are partially restrained by linear symmetric moorings fore and aft. The fluid motion is idealized as linearized, two-dimensional potential flow. The breakwater motions are assumed to be two-dimensional, in surge, heave and pitch. The solution for the fluid motion is obtained by the boundary integral equation method using an appropriate Green's function. Numerical results are presented that illustrate the effects of the various wave and structural parameters on the efficiency of the breakwaters as barriers to wave action. It is found that the wave reflection properties of the structures depend strongly on their width, draft and spacing and the mooring line stiffnesses, while their excess buoyancy is of lesser importance.  相似文献   

A new formula for front slope recession of berm breakwaters     

T. Lykke Andersen  H.F. Burcharth 《Coastal Engineering》2010

The front slope stability of breakwaters with a homogeneous berm was studied in a large number of two dimensional model tests at Aalborg University, Denmark. The results are presented together with a new formula for prediction of the berm recession which is the most important parameter for describing the reshaping. The formula has also been calibrated and validated against model test data from other researchers. The significance of the new design formula is that it predicts berm recession much better than the existing methods, especially in case of more stable structures.  相似文献   

Stability of highway embankments constructed on sloping ground against translational failure     

《Geomechanics and Geoengineering》2013,8(3):191-197

A translational failure of a highway embankment constructed on sloping ground may occur either in the mode of overall instability or in the mode of local instability. The stability analysis of the first mode is based on the assumption that the whole cross-section of the embankment will slide along the inclined base surface, whilst the second mode is based on the assumption of Rankine's active state of stress. In this paper the determination of the prevalent mode of failure – overall or local – is provided via a chart derived from force polygon analysis, with the dimensionless parameter, c′/γH, and the effective friction angle, φ′, as its axes. Furthermore, the determination of the most probable failure plane in the cross-section of the embankment is attempted and additionally the role of the cohesion in the stability is discussed. Finally, an estimation of the amplitude of failure at the road surface in the case of local instability is given. A confirmation of the aforementioned was achieved through case studies of highway embankments that have failed as a consequence of water infiltration and the development of high pore water pressures. A comparison between the local and the respective overall instability safety factor is given.  相似文献   

Equilibrium beach profile model for perched beaches     

M. Gonzlez  R. Medina  M. A. Losada 《Coastal Engineering》1999,36(4):777

A beach profile equilibrium model for perched beaches is presented. The model assumes that wave reflection at the seaward and leeward sides of the breakwater is the most important process that modifies Dean's equilibrium profile model for non-perched beaches. The influence of wave breaking over the submerged structure is also discussed. Several laboratory data sets are used to analyze the merit of the proposed model for describing the equilibrium condition of a perched beach. A good comparison is obtained. Results show that if the ratio between the water depth above the submerged structure, d, and the water depth at the toe of the structure, h_e, is large, d/h_e>0.5, only minor advance of the shoreline is achieved with the construction of a toe structure. A considerable advance is obtained for d/h_e less that 0.1. In these situations, however, resonant effects may result in an inefficient structure. The proposed model is used to provide an estimation for the required sand volume and the associated beach advance for the case of narrow breakwaters.  相似文献   

Observational Study of Surface Wind along a Sloping Surface over Mountainous Terrain during Winter     

Young-Hee LEE  Gyuwon LEE  Sangwon JOO  Kwang-Deuk AHN 《大气科学进展》2018,35(3):276-284

The 2018 Winter Olympic and Paralympic Games will be held in Pyeongchang, Korea, during February and March. We examined the near surface winds and wind gusts along the sloping surface at two outdoor venues in Pyeongchang during February and March using surface wind data. The outdoor venues are located in a complex, mountainous terrain, and hence the near-surface winds form intricate patterns due to the interplay between large-scale and locally forced winds. During February and March, the dominant wind at the ridge level is westerly; however, a significant wind direction change is observed along the sloping surface at the venues. The winds on the sloping surface are also influenced by thermal forcing,showing increased upslope flow during daytime. When neutral air flows over the hill, the windward and leeward flows show a significantly different behavior. A higher correlation of the wind speed between upper-and lower-level stations is shown in the windward region compared with the leeward region. The strong synoptic wind, small width of the ridge, and steep leeward ridge slope angle provide favorable conditions for flow separation at the leeward foot of the ridge. The gust factor increases with decreasing surface elevation and is larger during daytime than nighttime. A significantly large gust factor is also observed in the leeward region.  相似文献   

Caisson breakwaters embodying an OWC with a small opening—Part II: A small-scale field experiment     

Paolo Boccotti  Pasquale Filianoti  Vincenzo Fiamma  Felice Arena 《Ocean Engineering》2007,34(5-6):820-841

A common and intuitive idea is that, before an absorbing breakwater, waves are smaller than before a conventional reflecting breakwater. The theory of Part I has shown that, on the contrary, before a breakwater converter, in some cases, the wave height may be greater than before a conventional reflecting breakwater. Now, an experiment off the eastern coast of the Straits of Messina provides a confirmation of the theory: some huge amplifications of swells are common at a breakwater converter, and as a consequence the energy absorption gets very large. Here, we show the results of the experiment, and, basing ourselves on these results and on the theory of Part I, we suggest some practical way of calculation.  相似文献   

Multidirectional wave transformation around detached breakwaters     

S. Ilic  A.J. van der Westhuysen  J.A. Roelvink  A.J. Chadwick 《Coastal Engineering》2007

The performance of the new wave diffraction feature of the shallow-water spectral model SWAN, particularly its ability to predict the multidirectional wave transformation around shore-parallel emerged breakwaters is examined using laboratory and field data. Comparison between model predictions and field measurements of directional spectra was used to identify the importance of various wave transformation processes in the evolution of the directional wave field. First, the model was evaluated against laboratory measurements of diffracted multidirectional waves around a breakwater shoulder. Excellent agreement between the model predictions and measurements was found for broad frequency and directional spectra. The performance of the model worsened with decreasing frequency and directional spread. Next, the performance of the model with regard to diffraction–refraction was assessed for directional wave spectra around detached breakwaters. Seven different field cases were considered: three wind–sea spectra with broad frequency and directional distributions, each coming from a different direction; two swell–sea bimodal spectra; and two swell spectra with narrow frequency and directional distributions. The new diffraction functionality in SWAN improved the prediction of wave heights around shore-parallel breakwaters. Processes such as beach reflection and wave transmission through breakwaters seem to have a significant role on transformation of swell waves behind the breakwaters. Bottom friction and wave–current interactions were less important, while the difference in frequency and directional distribution might be associated with seiching.  相似文献