Uniform Slope Research Articles

A sheet erodibility parameter for water erosion modeling in regions with low intensity rain

Soil erodibility reflects the soil effect on the detachment process by rainfall and runoff; an evaluation of this parameter for single storm events was carried out using natural runoff plot data collected for two rainfall seasons in northern Iraq. The region is characterized by a semiarid Mediterranean-type climate with normal rainfall intensity below 20 mm/h and dominant sheet erosion on agricultural land. The plots were three 30 × 3 m and three 10 × 3 m, in fallow, situated on a 6% uniform slope; the soil at the site has a silty clay loam texture and belongs to the Calciorthid suborder. Sheet erosion rate was assumed linearly proportional to the storm power and the sheet flow power; a steady-state turbulent and kinematic sheet flow was also assumed. The results indicated a dominant detachment by rainfall with a substantial variability in storm by storm calculated sheet erodibility. The two-parameter lognormal probability distribution fitted the obtained sheet erodibility values reasonably well. Using this probability distribution, a representative sheet erodibility value of 0.056 × 10−3kg/J was obtained for use at the experimental site.

Effect of frontal slope on waveform evolution of a depression interfacial solitary wave across a trapezoidal obstacle

Waveform evolution associated with a depression interfacial solitary wave (ISW) over uniform slope or slope-shelf with different front slopes has been observed in many laboratory experiments and field studies since the 1980s, and by numerical modeling in more recent time. However, attention was mainly focused on waveform validation with KdV theory, wave run-up, reflection, energy dissipation and evolution on emergent mild uniform slope, rather on wave evolution and inversion across the plateau of a slope-shelf with steep front slopes, which are common in field conditions. Since it is often difficult to measure the entire process of waveform evolution in the field, laboratory experiments are adopted as an alternative to compliment field observations. This paper presents the results of laboratory experiments on ISW evolution across a submerged trapezoidal obstacle with four different front slopes, ranging from mild to very steep and vertical. Our results indicate that not only the likelihood of internal hydraulic jump, waveform inversion and the strength of internal wave breaking reduced, but more wave energy dissipated as well, as the front slope steepened. Upon using Hilbert–Huang transform to analyse the wave profiles recorded at four probe locations along the wave flume, the variability in the instantaneous characteristic wave period can be detected while an ISW propagated across a trapezoidal obstacle.

Dynamic monitoring of physical models beach morphodynamics and sediment transport using X-ray CT scanning technique

ABSTRACT Yamada, F., Tateyama, R., Tsujimoto, G., Suenaga, S., Long, B. and Pilot, C. 2013. Dynamic monitoring of physical models beach morphology and sediment transport using X-ray CT scanning technique A medical X-ray CT scanner was applied to dynamic measurements of beach profile changes, sedimentary structures, and sediment transport processes during wave actions in the laboratory experiments. An acrylic flume 7 m long and with an inner rectangular cross-section of 0.3 m × 0.3 m passes through the mobile gantry of a medical X-ray CT-scanner. The experiments were conducted at the Institut National de la Recherche Scientifique (INRS) at the University of Quebec from August 18 to October 16, 2011. The flume was filled with Ottawa sand (d50 = 0.147 mm) with uniform slope of 1/15. The water depth over a horizontal bed is 0.2 m. Regular waves were used with wave height of 4.0 cm and wave period of 0.7 s. In order to measure the cross-shore evolutions both of beach profiles and sediment transport process, th...

遡上波の力学的バランスと流れ構造

This paper presents fundamental features of flow structures and shear distributions in run-up waves on uniform slopes on the basis of experimental image experiments. It was found that there were high velocity gradients near the bottom and surface boundaries within the thin run-up water layer, resulting in multiple shear layers. The local flow structure in the run-up waves depends on the local surface gradient and shear distributions. Typical features of the boundary layer flows during run-up process are also discussed in this paper.

Identification of Forerunners and Transmission of Energy to Tsunami Waves Generated by Instanteneous Ground Motion on a Non-Uniformly Sloping Beach

The problem of generation and propagation of tsunami waves is mainly focused on plane beach, there are very few analytical works where wave generation is considered on non-uniformly sloping beach and as a result those works might have failed to capture important facts which are influenced by bottom-slope of the beach. Some researchers provided solution to the forced long linear waves but on a beach with uniform slope while the importance of including variable bottom topography is mentioned by few researchers but they also stayed away from considering continuous variability of the ocean bed as they were studying runup problem. This paper analyzes tsunami waves which are generated by instantaneous bottom dislocation on a ocean floor with variable slope of the form y=-qxr, q > 0, r > 0. Attempts are made to find analytical solution of the problem and along the way tsunami forerunners are identified while investigating the short time wave behavior, not found even with constant slope beaches. In our study a rather significant phenomenon with regard to energy transmission to the waves at steady-state are observed with some notable features.

WAVE RUNUP ON DIKES AND BEACHES

In the United States, the Federal Emergency Management Agency (FEMA) is in the process of updating its coastal flood risk maps in order to determine which locations are threatened by storm surge and wave action. These maps require the prediction of extreme wave runup. A method for predicting the runup height along the entire coast must be robust, reliable, and applicable to many different coastal features. Kobayashi et al. (2008) developed a time-average probabilistic model that predicts wave runup statistics instead of the time series of shoreline elevation. This numerical cross-shore model, CSHORE, is extended to the wet-dry zone above the still water level to predict irregular wave runup on impermeable dikes and gentle impermeable slopes. To show the CSHORE's capability in predicting runup on beaches with different geometries, the computed results from the model are compared to measured data from a variety of experiments. CSHORE is tested against 40 wave runup tests on an impermeable dike on a barred beach, 97 wave runup tests on an impermeable dike with a gently sloping beach, and 120 tests for wave runup on gentle uniform slopes. The measured 2% and 1% exceedence runup heights are predicted within errors of about 20%. The spectral significant wave height, Hmo, and a representative period are used for input to CSHORE.
 The measured and computed cross-shore variations of Hmo are also computed and compared to measured data to show the capabilities and limitations of CSHORE in regards to predicting to wave transformation. Both the spectral period, Tm-1,0, and the peak period Tp at x = 0 are adapted as representative periods used in CSHORE to assess the period effect in CSHORE. The tested CSHORE is ready for practical applications such as FEMA's coastal flood mapping, and is a good practical choice because it can be used to predict beach and dune profile changes.

Design of Nonzero Uniformly Sloping Laterals in Trickle Irrigation Systems

An analytical method was developed to design evenly sloping, pressurized, nontapered, multiple-outlet pipes. Assuming spatiotemporal continuity of emitter flow rates, the approach was derived from the solution of analytical nonlinear differential equations. A straightforward relationship was established between the inlet discharge, the lateral slope, the diameter, and the pressure head at the upstream and downstream ends. Five pressure head grade line profiles were derived: uniformly uphill, level ground, steeply downhill, moderately downhill, and slightly downhill. For moderately downhill laterals, the theoretical analysis revealed that the pressure head at the outermost rim was independent of the inlet discharge. For the other profiles, the pressure head at the downstream edge was parameterized as a function of the inlet discharge. The iterative computation of the inlet discharge is a prerequisite for the inference of the other design parameters. This approach was successfully compared with the stepwise method that is deemed to be the most accurate.

Design and Implementation of an Simulation of Water Wave Transformation Using Higher Order Mild-Slope Equation

A higher-order mild-slope equation (HOMSE) is derived based on theory of Hsu et al. [14]. Depth function is approximated up to third-order accurate in terms of both wave nonlinearity and bottom slope. Classical Galerkin method is used to solve HOMSE. Developed model is verified with a series of benchmark tests, including propagation of a sinusoidal wave past a submerged bar, wave propagating on a sloping bed, wave propagating over an elliptic shoal on a uniform slope, and wave propagating through a semicircular slope bottom, respectively. Computed results are compared with experiment data and prediction of low-order mild-slope equation model as well as Boussinesq equations model, and show good agreement.

Residual currents over a uniform slope due to breaking of internal waves in a two‐layer system

Residual currents due to internal wave breaking on a uniform slope were investigated in a two‐layer system using laboratory experiments and numerical computations for different layer configurations. Internal wave‐induced currents over a slope were measured in an experimental tank using PIV and also reproduced by a hydrodynamic model to quantify the detailed velocity field. The present results reveal that the critical level derived from the KdV theorem is a useful parameter for classifying the dynamics of internal waves breaking over a slope. As the horizontal distance from the critical level point to the internal wave breaking point increases, internal waves break more dynamically over the slope. Consequently, residual currents are enhanced near the breaking point. These findings increase our capacity to understand flux paths of biological and chemical substances in the stratified coastal ocean.

RANS v2–f simulation of a swash event: Detailed flow structure

The flow structure of a swash event over a uniform slope is studied using a RANS-VOF numerical model coupled with a v2–f turbulence closure. The model is compared with experimental data of recent laboratory experiments. The ability of the turbulence modelling for simulating swash flow and the evolution of the computed bed shear stress during run-up and run-down are investigated. The agreement between numerical results and measured data, such as water depth, depth-averaged velocity and bed shear stress is very good during run-up. Main discrepancies are found during run-down. The paper also examines the aeration of the water layer in the swash flow, taking advantage of the PLIC method for computing the air–water interfaces. Air is continuously entrapped in the swash front and released at its rear during run-up. A detailed analysis indicates that the flow reversal is initiated near the bottom at the outer boundary of the swash zone and progresses landward. The study highlights the asymmetry between run-up and run-down. During run-up, the swash front propagation determines the turbulence properties and the bed shear stress profile on the beach, whereas the flow properties are more homogeneously distributed in the swash area during run-down.

Elementary theory of bed‐sediment entrainment by debris flows and avalanches

Analyses of mass and momentum exchange between a debris flow or avalanche and an underlying sediment layer aid interpretations and predictions of bed‐sediment entrainment rates. A preliminary analysis assesses the behavior of a Coulomb slide block that entrains bed material as it descends a uniform slope. The analysis demonstrates that the block's momentum can grow unstably, even in the presence of limited entrainment efficiency. A more‐detailed, depth‐integrated continuum analysis of interacting, deformable bodies identifies mechanical controls on entrainment efficiency, and shows that entrainment rates satisfy a jump condition that involves shear‐traction and velocity discontinuities at the flow‐bed boundary. Explicit predictions of the entrainment rateEresult from making reasonable assumptions about flow velocity profiles and boundary shear tractions. For Coulomb‐friction tractions, predicted entrainment rates are sensitive to pore fluid pressures that develop in bed sediment as it is overridden. In the simplest scenario the bed sediment liquefies completely, and the entrainment‐rate equation reduces toE = 2μ1gh1 cos θ(1 − λ1)/ , where θ is the slope angle, μ1 is the flow's Coulomb friction coefficient, h1 is its thickness, λ1 is its degree of liquefaction, and is its depth‐averaged velocity. For values ofλ1ranging from 0.5 to 0.8, this equation predicts entrainment rates consistent with rates of 0.05 to 0.1 m/s measured in large‐scale debris‐flow experiments in which wet sediment beds liquefied almost completely. The propensity for bed liquefaction depends on several factors, including sediment porosity, permeability, and thickness, and rates of compression and shear deformation that occur when beds are overridden.

Interaction between Tsunami Waves and Isolated Conical Islands

Abstract Chen, J.M.; Liang, D., and Tang, H., 2012. Interaction between tsunami waves and isolated conical islands. A newly developed computer model, which solves the horizontal two-dimensional Boussinesq equations using a total variation diminishing Lax-Wendroff scheme, has been used to study the runup of solitary waves, with various heights, on idealized conical islands consisting of side slopes of different angles. This numerical model has first been validated against high-quality laboratory measurements of solitary wave runups on a uniform plane slope and on an isoliated conical island, with satisfactory agreement being achieved. An extensive parametric study concerning the effects of the wave height and island slope on the solitary wave runup has subsequently been carried out. Strong wave shoaling and diffraction effects have been observed for all the cases investigated. The relationship between the runup height and wave height has been obtained and compared with that for the case on uniform plane sl...

Influence of Anisotropic Internal Friction Angle on the Stability of Uniform Soil Slopes

The effect of anisotropy of friction angle in natural deposited soil on the stability of soil slopes was studied in this paper. Stability analysis was performed on a uniform soil slope with anisotropic friction angle. Spencer’s method was used, and the variation of friction angle was assumed to be linear to the change of direction of the slip surface. It was shown that 7-10 percent of change in safety factor might achieve within a 10m-highed anisotropic soil slope. It was also found from the analysis that that frictional anisotropy had no obvious effect on the location of critical slip surface.

Searching for the Central Coordinates of Critical Failure Surface Based on Simplified Bishop Method

Central coordinates of the critical failure surface of uniform slope are searched by using procedural Simplified Bishop equation. Comparison of stability factor K calculated by the program with existing ones shows that the program is available. The sensibilities of the factors influencing on slope stability are analyzed by orthogonal test method. The results indicate that the sensibilities of the factors are as follows in their magnitude order: slope height H, ratio m, internal friction angle φ, cohesion c and unit weight γ. Central coordinates of the critical failure surface is located at center of the K contours, the results of Fellenius straight-line method and Taylor chart method are different from the program’s. The fitting curves of central coordinates change with γtanφ/c and the corrected values are obtained based on a large number of calculations. It can be conveniently used in actual engineering.

Effects of Monovegetation Restoration Types on Soil Water Distribution and Balance on a Hillslope in Northern Loess Plateau of China

In the Loess Plateau of China, mosaic-vegetation restoration by converting cropland into fallow (to regenerate natural vegetations) and perennials performs well in soil erosion control. However, soil desiccation caused by the planted perennials threatens the sustainability of vegetation restoration. Understanding of soil water distribution and balance in monovegetation systems at hillslope scale is crucial for building a constructive mosaic-vegetation restoration pattern in the Northern Loess Plateau. The objectives in this study were to investigate effects of monovegetation restoration types on soil water distribution and balance and discuss the possible implications of the monovegetation hydrological properties for mosaic-vegetation pattern establishment at hillslope scale. In 2004, the authors chose a one-piece waste hillslope with uniform slope of 12 degrees and established four monovegetation plots subjected to shrub, grass, fallow, and cropland. Shrub, grass, and fallow are the typical vegetation restoration types, whereas cropland presents the traditional land use. Soil water content profiles, down to 400-600 cm depth, along the hillslope were measured with a neutron moisture meter from May-October in 2004, 2008, and 2009. Results showed that the rainfall infiltration depth was approximately 100 cm for shrub and grass but exceeded 300 cm for fallow and cropland. Six growth years later, shrub, grass, and fallow depleted more soil water than cropland, in the amount of 288, 313, and 62 mm, respectively. Soil water depletion in shrub and grass resulted in dried soil layers at the depth of 100-260 cm and 100-360 cm. Water balance results indicated that soil water deficit occurred in June during the rain season. The authors observed that downhill-accumulation of soil water storage, down to 400 cm depth, existed for fallow and cropland in 2004 and 2009. However, 6 growth years of shrub and grass substantially weakened such soil water downhill-accumulation tendency. This fact alone suggests that a mosaic vegetation system of planting shrub/grass downhill and setting fallow uphill would be appropriate from a standpoint of maintaining the sustainable development of vegetation restoration in the study area. Further experiments should be performed to develop the mosaic-vegetation patterns meeting the interests of both erosion control and sustainability of vegetation restoration. DOI:10.1061/(ASCE)HE.1943-5584.0000628. (C) 2013 American Society of Civil Engineers.

QUICK EVALUATION OF RUNUP HEIGHT AND INUNDATION AREA FOR EARLY WARNING OF TSUNAMI

A methodology combining the offshore tsunami calculated by using numerical reciprocal Green's function (RGF) and the runup flow field calculated by using an analytical Green's function (AGF) is proposed to quickly estimate a tsunami hazard.For a vulnerable city, the RGF is computed previously via linear shallow water equations over real bathymetry and the offshore tsunami can be obtained promptly once the initial rupture is known. A transformation from time to space is then applied to obtain an equivalent waveform. With an integral with the AGF, derived by Carrier et al. [2003] based on 1D fully nonlinear shallow water equations over a uniform constant slope, the runup flow field is calculated. Thus, besides saving computation time and reducing the memory requirement, the desired initial condition for the AGF can also be generate by RGF. In this approach, the max wave height and the inundation distance are estimated very quickly and can be applied to broadcast an early warning of tsunami.To verify the method, data obtained during the 2004 Indian Ocean Tsunami from Sri Lanka and Phuket, Thailand is applied. The offshore condition is first verified by comparing with the record at Maldives. The accuracy of RGF is also tested. Then, by taking the nearshore shelf slope as the constant bottom slope for the analytical solution, the max tsunami height agrees reasonably well with the in-situ measurement. Therefore, this method is a useful tool for tsunami early warning by quickly estimating if the max wave height is higher than the seawall or the breakwater. The max inundation distance calculated by the analytic integral solution also has reasonable agreement with the field survey, but the value from the in-situ investigation scatters widely, which suggests that the detailed local topography plays an important role. A different method for the determination of the bottom slope is also tested and the result shows that the slope should be based on the bathymetry nearshore.

Assessment of the major hazard potential of interfacial solitary waves moving over a trapezoidal obstacle on a horizontal plateau

Over the last few decades, a lot of attention has been concentrated on the consequences of marine impacts, especially those caused by the tsunami wave train. Internal solitary waves are similar to the surface waves that commonly occur in the waters of the ocean or large lakes and can have significant effects on oceanic mixing, climate change, the movement of submerged plankton, and the weathering of geological structures. This motion can be severe enough to create natural hazards such as submarine tsunamis in the ocean. These could also even occur in large lakes. The present work aims to contribute to this knowledge base by studying internal wave propagation on a shallow continental shelf following a particular marine impact. A series of laboratory experiments were conducted in order to clarify the movement of an interfacial solitary wave across a uniform slope and a horizontal plateau forming a slope-shelf topography. The results obtained from test runs indicate that the wave maintains its strength, having a direct impact on the natural ecology of the local oceanic environment. Comparison with different seabed topographies is also presented to demonstrate the propagation of an internal wave over a trapezoidal barrier. A better fitting and more appropriate model is employed to examine the relationship between the physical parameters for better predicting the evolution of an internal solitary wave as it moves over a trapezoidal obstacle on a horizontal plateau.

Influence of thermomechanics in the catastrophic collapse of planar landslides

Frictional heating has long been considered a mechanism responsible for the high velocities and long run-out of some large-scale landslides. In this work a landslide model is presented, applicable to large-scale planar landslides occurring in a coherent fashion. The model accounts for temperature rise in the slip zone due to the heat produced by friction, leading to water expansion, thermoplastic collapse of the soil skeleton, and subsequently to an increase of pore-water pressure. The landslide model, comprising equations that describe heat and pore pressure diffusion and the dynamics of the moving mass, is used to analyse the evolution of the Jiufengershan planar landslide as an example. Further, its parameter space is systematically and efficiently explored using a Taguchi parametric analysis in an attempt to quantify dominant parameters. It is shown that the process of sliding is dominated by the softening properties of the material, as expected, but also by the permeability of the slip zone and the thickness of the sliding mass. It is worth noting that the latter two parameters do not enter traditional stability analyses of uniform slopes.

Internal wave–turbulence pressure above sloping sea bottoms

An accurate bottom pressure sensor has been moored at different sites varying from a shallow sea strait via open ocean guyots to a 1900 m deep Gulf of Mexico. All sites show more or less sloping bottom topography. Focusing on frequencies (sigma) higher than tidal, the pressure records are remarkably similar, to within the 95% statistical significance bounds, in the internal gravity wave continuum (IWC) band up to buoyancy frequency N. The IWC has a relatively uniform spectral slope: log(P(sigma)) = -alpha log(sigma), alpha = 2 +/- 1/3. The spectral collapse is confirmed from independent internal hydrostatic pressure estimate, which suggests a saturated IWC. For sigma > N, all pressure-spectra transit to a bulge that differs in magnitude. This bulge is commonly attributed to long surface waves. For the present data it is suggested to be due to stratified turbulence-internal wave coupling, which is typically large over sloping topography. The bulge drops off at a more or less common frequency of 2-3 x 10(-2) Hz, which is probably related with typical turbulent overturning scales.

DCIV measurements of flow fields and turbulence in waves breaking over a bar

The experimental investigation of laboratory waves breaking over a bottom topography resembling a bar is presented in this paper. The experiments were conducted in a glass flume. The instantaneous velocity fields were measured using a video based digital correlation image velocimetry (DCIV). Measurements of velocities were restricted to positions shorewards of the bar crest. Measurements of time averaged velocities, turbulence intensities and turbulent kinetic energies that span the entire water column are provided. As the plunging-like wave at the crest of the bar turns into a spilling-like wave with increasing depth on-shore of the bar, it is shown that a limited transfer of TKE down to the bed is observed compared to spilling breakers on uniform slopes.