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This paper analyses an important aspect of the continuum numerical modelling of rapid landslides as debris flows: “By using the same rheological parameter values, are the results obtained with codes that implement the same constitutive equations, but a different numerical solver, equal?” To answer this question, the two numerical codes RASH3D and GeoFlow_SPH are used here to back-analyse the debris flow event that occurred in the Nora stream (northwestern Italian Alps) in October 2000. Comparison of results evidenced that the RASH3D best-fit rheological values for the Nora event back-analysis overestimated both the final depositional heights and the simulated flow velocities if used in GeoFlow_SPH. To obtain thickness values comparable with those measured in situ, it was necessary to re-calibrate GeoFlow_SPH rheological parameter values. This way, with the exception of a larger lateral spreading of the sliding mass given by RASH3D, both thickness and velocity values were similar for the two numerical codes.

A depth-averaged two-phase model is proposed for debris flows over fixed beds, explicitly incorporating interphase and particle-particle interactions, fluid and solid fluctuations and multi grain sizes. A first-order model based on the kinetic theory of granular flows is employed to determine the stresses due to solid fluctuations, while the turbulent kinetic energy - dissipation rate model is used to determine the stresses from fluid fluctuations. A well-balanced numerical algorithm is applied to solve the governing equations. The present model is benchmarked against USGS experimental debris flows over fixed beds. Incorporating the stresses due to fluid and solid fluctuations and properly estimating the bed shear stresses are shown to be crucial for reproducing the debris flows. Longitudinal particle segregation is resolved, demonstrating coarser sediments around the fronts and finer grains trailing the head. Based on extended modeling exercises, debris flow efficiency is shown to increase with initial volume, which is underpinned by observed datasets.

Flow-like landslides commonly happen in mountainous areas and may cause economic and human life losses in the impacted areas. Computer modelling has become an effective tool for landslide risk assessment and reduction. Models based on discrete element method (DEM) have been widely used for landslide prediction; however, this method is computationally too demanding for large-scale applications. Depth-averaged models (DAMs) have been widely reported for simulating run-out and deposition of flow-like landslides over large spatial domains due to its relatively higher computational efficiency. To combine the advantages of both types of modelling approaches, this work introduces a novel landslide model developed by coupling a DEM model with DAM for simulation of flow-like landslides, in which the DEM is employed in the landslide initiation area to better simulate the failure mechanism of slope, and the DAM is adopted in the landslide runout and deposition phase, where the landslide has developed into flow-like landslide with fluid-like behaviour. Finally, the new coupled model is validated against an experimental test case. Satisfactory results have been obtained, demonstrating that the coupled model is able to accurately capture the detailed dynamics of flow-like landslides.

Irregular, unauthorized and non-technical mining of sand and gravel from rivers play an important role in undesirable changes in morphology and environment. The present experimental study investigated sand mining pit modelling in the different scenarios. A two-dimensional flexible mesh, depth averaged model was set-up to simulate the experiments. The results exhibited an acceptable agreement between the numerical and experimental results, so that the maximum error was limited to less than 10%. After verifying the numerical model, a critical reach in Helleh River was selected as a case study. The effect of sand and gravel mining on a bridge at the site was studied. The results also indicated that for a flood event with a return period of 25 years, sand and gravel mining changed the bed profile up to 1.27 m at the bridge foundation. Moreover, initial signs of river meandering emerged in one scenario.

천이류와 같은 급변류에 의한 하상변동을 예측하기 위한 이차정확도의 유한체적법 모형을 제시하였다. 부정류 조건하에서의 유사이송과 하상변동문제에 적용하기 위하여 유사이송모형을 천수방정식과 연계하였다. 지배방정식은 MUSCL 기반의 유한체적법을 이용하였고, 계산요소간 흐름률은 HLLC approximate Riemann solver를 이용하여 계산하였다. 일차원과 이차원 수로에서의 댐붕괴파에 의한 하상변동문제와 월류로 인한 하류부 댐사면의 침식문제에 적용한 결과, 적정한 매개변수를 이용하는 경우에 전반적으로 정확한 수치모의 결과를 얻을 수 있었다. 또한 전반적인 계산결과는 수치적으로 안정적이고 물리적으로 타당한 결과를 나타내었고, 이로부터 제시된 수치모의 기법이 상류와 사류조건하에서의 하상변동 문제에 적용이 가능할 것으로 판단된다. 【A stable second-order finite volume method was proposed to predict sediment transport under rapidly varied flow conditions such as transcritical flow. For the use under unsteady flow conditions, a sediment transport model was coupled with shallow water equations. HLLC approximate Riemann solver based on a monotone upstream-centered schemes for conservation laws (MUSCL) reconstruction was used for the computation of the flux terms. From the comparisons of dam break flow experiments on erodible beds in one- and two-dimensional channels, good agreements were obtained when proper parameters were provided. Lastly, dam surface erosion problem by overtopped water was simulated. Overall, the numerical solutions showed reasonable results, which demonstrated that the proposed numerical scheme could provide stable and physical results in the cases of subcritical and supercritical flow conditions.】

Lateral distributions of depth-averaged velocity in open compound channels with submerged vegetated floodplains are analyzed, based on an analytical solution to the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term included to account for the effects of vegetation. The cases of open channels are: rectangular channel with submerged vegetated corner, and compound channel with submerged vegetated floodplain. The present paper proposes a method for predicting lateral distribution of the depth-averaged velocity with submerged vegetated floodplains. The method is based on a two-layer approach where flow above and through the vegetation layer is described separately. An experiment in compound channel with submerged vegetated floodplain is carried out for the present research. The analytical solutions of the three cases are compared with experimental data. The corresponding analytical depth-averaged velocity distributions show good agreement with the experimental data.

The local scour depth is a key parameter in the design of levee engineering. Based on experiment data, a non-dimensional analysis for the prediction of local scour depth is related to the approach flow velocity, flow depth, flow angle, scope of levee and the particle size of the bed sediment. The results of this study indicate that the local scour depth increases with the depth averaged velocity and junction angle. Finally, an empirical formula of predicting the gravel channel maximum scouring depth was developed and tested with the experimental data.

Many rivers in Taiwan have steep slopes, are subject to typhoon-induced flood flows, and contain soft bedrock that is exposed at many locations and easily erodible. The occurrence of extensive bedrock erosion has been a major threat to river infrastructure at many locations. Soft bedrock erosion, therefore, is an important process to consider for river projects in Taiwan. In this study, bedrock erosion models are reviewed. A specific model is proposed by combining two existing models incorporating both the hydraulic and abrasive scour mechanisms. The proposed bedrock erosion model is incorporated into a two-dimensional mobile-bed model, and the integrated model is tested by simulating bedrock erosion downstream of the Chi-Chi weir on the Choshui River in Taiwan. A calibration study is performed to determine appropriate values of the model parameters based on two and a half years of measured data. The model is then assessed based on a verification study that compares model predictions of bedrock erosion of...

Contraction scour is often encountered in natural rivers due to natural geological controls, bridges, or river restoration structures. Such scour may be better predicted with multi-dimensional than one-dimensional models. The aim of this study is to investigate whether a two-dimensional depth-averaged model is adequate for modelling contraction scour. This study shows that improved predictions are obtained with the present model relative to previous model investigations. The study also shows that the current model is adequate for predicting contraction scour and model results are comparable with those of three-dimensional modelling except for the prediction of aggradation downstream of the contracted channel section.

This paper presents a method to predict depth-averaged velocity and bed shear stress for overbank flows in straight rectangular two-stage channels. An analytical solution to the depth-integrated Navier–Stokes equation is presented that includes the effects of bed friction, lateral turbulence, and secondary flows. The Shiono and Knight method accounts for bed shear, lateral shear, and secondary flow effects via three coefficients, f , λ , and Γ , respectively. A novel boundary condition at the internal wall between the main channel and the adjoined floodplain is proposed and discussed along with other conventional boundary conditions. The analytical solution using the novel boundary condition gives good prediction of both lateral velocity distribution and bed shear stress when compared with experimental data for different aspect ratios.

A nonlinear analysis procedure has been proposed to simulate the spatial variation of velocity profile of pressurized laminar flows between wavy boundaries as an idealized flow model in rock fractures. The main objective of this analysis is to refine the depth averaged flow model for a rock joint, reflecting the results of this analysis. The analysis is based on an assumed general form of velocity profile in the direction of flow, whereby the unknowns are determined through the use of the continuity and momentum equations. Comparison is made between the 2D-vertical model's results and the nonlinear solution through which the applicability of the analysis is verified. The nonlinear solution shows good agreement with the 2D-vertical model's results especially for small amplitude-to-wavelength ratio of the wavy boundaries, but enough to reveal the velocity profile's deformation.

A comparison of four methods for predicting the incipient motion conditions of a uniform sand bed is presented. The four methods are: (1) the Shields diagram, (2) an empirical approach, (3) a method derived from resolution of rotational forces, and (4) a simplified resolution of rotational forces with a variable lift force coefficient. The four methods are used to predict the incipient motion conditions for 97 experimental runs taken from seven independent experimental flume studies. The effectiveness of predicting depth averaged incipient motion velocity for each of the four methods are compared. The simplified resolution of rotational forces model (4) and Shields method (1) were most successful in predicting the incipient motion velocity [R2=0.77, 0.74 and root mean square error (RMSE)=0.18, 0.15, respectively]. The slope of line of best fit for plots illustrating predicted versus measured incipient motion velocity were similar (slope=0.63, 0.65, respectively), illustrating that both methods provide a s...

A flow resistance in a river changes with development or attenuation of sand waves. Therefore, it is necessary to know how the flow resistance varies with transformation of sand bed, in order to predict the water surface variations. In this study, the numerical model to reproduce the formation processes of dunes was developed. A depth averaged flow model considering the effects of vertical acceleration and a nonequilibrium sediment transport model is combined. Calculated results on the temporal development processes, the shape characteristics of dunes and flow resistance are compared with previous experimental studies.

In this short communication the four estimate criteria of the depth-averaged local velocity proposed by Byrd et al. (Earth Surface Processes and Landforms, 2000, Vol. 25, pp. 167-173) are compared both with the three-point method of Bathurst and with the average velocity obtained by integrating the velocity profile (FPa2) suggested by Ferro and Pecoraro (Water Resources Research, 2000, vol. 36, pp. 2761-2770). The comparison was carried out using 84 velocity profiles measured by an acoustic Doppler velocimeter in a rectangular flume with a gravel bed. Copyright © 2002 John Wiley and Sons, Ltd.

The Suez Canal is an important water-transport route all over the world. Two hydrodynamic issues related to the flow within the canal are worthy of consideration: sedimentation in the northern section of the canal and high velocity current in the southern section of the canal. To address the sedimentation issue, a large program of dredging works is being undertaken. A numerical model is presently being developed to simulate flow in the canal with a special attention paid to the south part. This model is the focus of the present study. The model is a two-dimensional depth averaged finite element model utilizing independent open boundaries at the north and south ends of the canal. The radiation and modified long wave boundary conditions are compared. Due to its accuracy and flexibility to suit different forcing conditions, the radiation boundary condition shows superiority over the modified long-wave formulation. The simulation results reflect most of the physical phenomena observed in the canal.

Diffusion and deposition of sediment in a sea area have caused serious problems in various situations. Thus, it has been required to predict the distribution of the sediment more accurately to takesteps.For horizontally large flow fields having particle sources with well-mixed cross sections, we had proposed the depth-averaged model for diffusion and deposition of settling particles by adopting the result of the numerical research by Jobson and Sayre (1970). In this paper, we improved this model to be adaptable to a flow field having a particle source near a water surface or a bottom region. In addition, the new model was applied to simulate the distribution of the sediment generated by the reclamation in Kawatana Port.As a result of this research, it was confirmed that the present model would make it possible to predict a more accurate distribution of sediment in a nearly-plane sea area.

本研究は, 小規模河床波の発達領域までを再現するために, 実用的には水深積分モデルが便利との観点から, 流れの非回転条件と加速・減速効果を考慮することにより流速分布の局所的な変化を積分モデルに導入し, 波状路床上の底面せん断応力分布を解析する方法を示した. 基礎式は鉛直加速度を考慮した水面形方程式であり, 摂動法により導かれた基礎式の2次までの解を求めるとともに, 底面せん断応力分布に関する従来の実験結果と比較することにより, 解析法の適用性を検証した.

Bank erosion in populated areas could cause fatalities and property damage if banks collapse abruptly, compromising the integrity of residential buildings and civil facilities. Bank erosion study is in general a very complex problem because of it involves multi-processes such as bank surface erosion, bank toe erosion and bank material mechanic failure, etc. Each of these processes is related to several parameters: sediment size distribution, bank material cohesion, slope, homogeneity, consolidation, soil moisture and ground water level, as well as bank height. The bank erosion rate is also related to the strength of the flow in the river indicated by the flow shear stress, water depth and channel curvature, etc. In this study, the numerical model CCHE2D has been applied to study real-world bank erosion cases in a mountain river, Khoske Rud Farsan River, Iran, which is a braided river with high sediment loads and channel mobility; the bank erosion of this river is dominated by floods during rainy seasons.

A novel technique was proposed to calculate fluxes accurately by separation of flow area into a part of step face which is dominated by flow resistance of it and an upper part which is relatively less affected by the step face in analyzing shallow-water flows over discontinuous topography. This technique gives fairly good agreement with exact solutions, 3D simulations, and experimental results. It has been possible to directly analyze shallow-water flows over discontinuous topography by the technique developed in this study. It is expected to apply the developed technique to accurate evaluation of overflows over weirs or retaining walls (riverside roads) and areas flooded by the inundation in the city covered in discontinuous topography.

Two-dimensional dispersion model (DISP2D), based on the stream tube concept, has been developed to predict the depth averaged concentration distribution in channels under steady flow conditions. Such water quality model is not feasible for the practical engineering use for channels in case of lacking enough hydraulic data. In this paper, it is intended to couple the DISP2D model with one hydrodynamic model to make the model powerful and feasible. The proposed hydrodynamic model is based on the depth averaged longitudinal momentum equation. To solve the hydrodynamic model numerically, some assumptions have been made to take into account the effect of secondary currents. The flow model was tested using data on prismatic flumes with compound cross-sections. The integrated hydrodynamic and dispersion model was further examine by using the measured velocity and concentration data. Comparison shows that the predicted lateral flow and concentration distributions are in good agreement with the measured data. Successful applications indicate that the proposed model can be used for simulating flow and contaminant transport in open channels.

Results of two-dimensional (depth averaged) and three dimensional computations of a 1750m reach of the Sacramento River are compared with velocity data obtained in a large-scale, distorted physical model of the same reach. The aim was to predict the level of modeling required to predict the occurrence of bank erosion observed in the field. Further results are presented which show the outcome of deploying 5 groins to inhibit bank erosion upstream of a bridge abutment. The simulations are also compared with experimental data to assess the performance of alternative shear formulae. Truncation errors are estimated using two alternative techniques. The results suggest that the occurrence and mitigation of bank erosion in large natural river systems can be predicted to an acceptable degree of accuracy.

A willow post system is a type of bioengineering system used to reduce streambank erosion. In essence, a willow post system is a collection of rigid cylinders placed along a streambank. Herein, an analytical model that was developed to evaluate the hydrodynamics of newly constructed willow post systems is reviewed. The model is founded on wake theory and was originally developed for predicting depth-averaged velocities in straight trapezoidal channels with unsubmerged rigid cylinders. The model was recently modified and now includes a parameter for evaluating submerged vegetation and is referred to as the submergence ratio. Observed depth-averaged velocities from a physical model study are compared to predicted depth-averaged velocities from the original and the modified version of the analytical model. A comparison of coefficient of determination (r 2 ) values shows that the submergence ratio significantly improves the accuracy of predicted velocities in channels with submerged and unsubmerged vegetation.

The bed stress under breaking solitary wave runup was investigated in this study using the Simultaneous Coupling Method (SCM). The SCM couples the shallow water equation (SWE) with k-w model. The depth averaged velocity from SWE is applied as the upper boundary condition in k-w model for bed stress assessment from the boundary layer. It was found that the boundary layer approach provides more accurate bed stress estimation than the empirical method, which leads to a more accurate prediction of runup and wave profile. The accumulation of bed stress in during solitary wave runup was evaluated. The bed stress on the direction leaving the shoreline will have more impact in the overall process. However, during a short period of run up process, bed stress toward the shoreline may have significant effect as well.

Note: [451] Reference LCH-ARTICLE-2005-004View record in Web of Science Record created on 2007-04-24, modified on 2016-08-08