Chaiyuth Chinnarasri

Numerical modelling of dam failure due to flow overtopping

Abstract A one-dimensional numerical model for dam failure due to flow overtopping is developed. The MacCormack explicit finite difference scheme is used to solve the one-dimensional equations of continuity and momentum for unsteady varied flow over steep bed slopes. In the computation of erosion process, sediment transport equations are considered and the modified Smart formula developed for steep bed slope is selected. The sliding stability of the overtopped dam is checked by modified ordinary method of slices. The model has been successfully calibrated and verified using laboratory experimental data. By comparing with the experimental results, it was found that the model accuracy depends largely on the sediment transport formula and pore water pressure coefficient. The model was found to predict actual breach outflow of the Buffalo Creek Dam reasonably well and closer than other existing numerical models.

Embankment dam breach and its outflow characteristics

With nine experimental data, the correlations of important relevant variables to the embankment-breaching phenomena are proposed. During the rise of the outflow through the breach, the amount of outflow depends largely on the breach size. The averaged final breach width is found to be in the range of , where H d is the original dam height. The peak outflow through a breach (Q p) for non-cohesive homogeneous embankment is correlated from the present measured data and the number of historical data. In addition, the relation of breach deformation time (t f) is also presented. This depends largely on the characteristics of reservoir shape and peak outflow through the breach. Given a specified reservoir volume, the breach deformation time can be extended when a smaller median grain size of soil and a flatter slope of the downstream embankment dam are used.

Effects of rainfall intensity and slope gradient on the application of vetiver grass mulch in soil and water conservation

Abstract The objective of this study is to investigate the effect of rainfall intensity and slope gradient on the performance of vetiver grass mulch(VGM) in soil and water conservation. The study involved field experiments on 2m × 10m plots with 2 slopes of 3% and 30%. Two rainfall intensities of 55 mm hr −1 and 140 mm hr −1 were selected with a 1 hr for 2 year to 500 year return period. A set of artificial rainfall simulators was constructed and calibrated as part of the research project. Six dry matter quantities of VGM were used in the study. The runoff volume per unit surface area decreased with an increase in the quantity of VGM. For the 3% land slope, they varied from 5.6 to 13.4 mm and from 22.8 to 46.1 mm for rainfall intensities of 55 and 140 mm hr −1 , respectively. For the 30% land slope, they varied from 8.0 to 21.4 mm and from 29.4 to 59.6 mm for rainfall intensities of 55 and 140 mm hr −1 , respectively. The average soil losses were 0.32–2.85 kg m −2 on the bare soil plots, and 0.07–1.80 kg m −2 on the VGM plots. The VGM showed good potential for reducing runoff by 31.5–68.4% and soil loss by 33.7–82.4%, compared with the case without VGM. The quantity of VGM equal to 0.75 kg m −2 presented the best performance in reducing runoff and soil loss.

Non-linear turbulence models for multiphase recirculating free-surface flow over stepped spillways

The flow over a stepped spillway is free surface, multiphase and turbulent. Moreover, a recirculation region occurs at each step of the spillway. The flow characteristic is hence complicated and difficult to predict. In previous work on stepped spillways (Chen et al. Journal of Hydraulic Engineering, ASCE, 128 (7), 683–688 and Xiangju et al. Science in China Series E: Technological Sciences, 49 (3), 674–684), only the linear turbulence model was applied which gave low accuracy. Furthermore, there are still no optimised model constants for this kind of flow. The present work therefore aims to apply the large eddy simulation (LES), the non-linear and the modified non-linear turbulence models to simulate the flow over the spillways with various slopes and step heights. It is found that the modified model is able to predict the flow close to the LES but requires less computational time by a factor of up to 4. Moreover, the modified model gives higher accuracy than the LES for the cases of the spillways with higher slopes and step heights.

Numerical simulation of flow velocity profiles along a stepped spillway

The velocity profiles on stepped spillways are analyzed using computational fluid dynamics simulations and large-scale laboratory experiments. Five different turbulence models are considered in the analysis: the Standard k-ɛ, the Realizable k-ɛ, the Renormalization group k-ɛ, the Standard k-ω and the Shear stress transport k-ω model. The computational fluid dynamics simulation results are compared with laboratory measurements from a large-scale physical model with flow velocities up to 15 m/s. It is indicated that the numerical model involving any of these turbulence models can satisfactorily simulate the velocity profiles. All five turbulence models performed satisfactorily well on large-scale stepped spillways. The k-ω models may be slightly better suited in the lower region, while the realizable k-ɛ model provided slightly better results in the upper part of the velocity profile. A power law with n = 5.09 also provides a useful first approximation with a limitation of the flow along stepped spillway with the Reynolds number of 1 . 68 × 10 6 ≤ Re ≤ 7 . 21 × 10 6 .

Field validation of two river morphological models on the Pasak River, Thailand

Abstract A comparison is made of the quasi-two-dimensional GSTARS2.1 mathematical model, which can analyse lateral erosion, and the well-known one-dimensional HEC-6 model. Also, both models are validated by means of comparison with observations. The study emphasizes the differences in principle, concept, results and efficiency of the two models. The morphological processes over the 56-km reach of the Pasak River, downstream of Pasakjolasid Dam in Thailand, are considered. The analysis was carried out on a 14-year continuous period (1990–2004). The computational results are compared with the observed data, collected from six river cross-sections in 1990 and 2004. Compared with the observed bed level data, the results computed by using HEC-6 and GSTARS2.1 are similar for one-dimensional simulation without the consideration of lateral change of bed elevation. However, when both bed change and lateral erosion were considered, the GSTARS2.1 model gave better agreement to the measured river cross-sections than the HEC-6 model, due to the advantage of the stream tube technique.