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Sadra Shadkani Akram Abbaspour Saeed Samadianfard Sajjad Hashemi Amirhosein Mosavi Shahab S.Band 《国际泥沙研究》2021,36(4):512-523
Monitoring sediment transport is essential for managing and maintaining rivers.Estimation of the sediment load in rivers is fundamental for the study of sediment movement,erosion,and flood control.In the current study,three machine learning models-multi-layer perceptron(MLP),multi-layer perceptron-stochastic gradient descent(MLP-SGD),and gradient boosted tree(GBT)-were utilized to estimate the suspended sediment load(SSL)at the St.Louis(SL)and Chester(CH)stations on the Mississippi River,U.S.Four evaluation criteria including the Correlation Coefficient(CC),Nash Sutcliffe Efficiency(NSE),Scatter Index(SI),and Willmott’s Index(WI)were utilized to evaluate the performance of the used models.A sensitivity analysis of the models to the input variables revealed that the current day discharge variable had the most effect on the SSL at both stations,but in the absence of current-day discharge data(Qt),a combination of input parameters including SSLt-3,SSLt-2,SSLt-1,Qt-3,Qt-2,Qt-1 can be used to estimate the SSL.The comparative outcomes indicated the high accuracy of MLP-SGD-5 model with a CC of 0.983,SI of 0.254,WI of 0.991,and NSE of 0.967 at station CH and the MLP-SGD-6 model with a CC of 0.933,SI of 0.576,WI of 0.961,and NSE of 0.867,respectively,at station SL.The results of MLP models were improved by SGD optimization.Therefore,the MLP-SGD method is recommended as the most accurate model for SSL estimation. 相似文献
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One of the main problems in reservoirs is sedimentation which reduces the operating life of dams if a proper plan and analysis method are not in place.The techniques to manage sediment in reservoirs include several sustainable management techniques that route sediment through or around the reservoir.One of the main economical methods in arid and semi-arid regions is pressurized flushing using moderate drawdown of the water level of the reservoir to evacuate sediment deposited behind dams.In the current study,the effect of a new structure called a dendritic bottomless extended(DBE)outlet structure at three angles of 30°,45°,and 60°on pressurized flushing efficiency was investigated.Consequently,45 experiments were designed for three discharge rates (Qo),three sediment levels(Hs),four types of structure,and a no-structure condition(reference test).The results indicated that the DBE structure with a 30°angle between the branches,a sedimentary dimensionless index of Hs/Do=4.59,and a flow dimensionless index of Qo=/√gD05=1:43(where g is the acceleration of gravity and Do is the diameter of the bottom outlet)lead to 10-fold increase in the sediment flushing cone dimensions and sediment removal efficiency compared to the results of the reference test.Finally,according to a statistical analysis of the results,a dimensionless equation for calculating the sediment flushing cone dimensions was developed for the tested sediment characteristics. 相似文献
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《国际泥沙研究》2020,35(2):125-133
The current study modifies the representation of the Shields parameter using turbulent strength,i.e.the root-mean-square(rms) fluid velocity.Experiments were done under a steady,uniform flow using eight sediment sizes with particle Reynolds numbers(Rep) ranging between 1.0(fine sediment) and 183.4(coarse sediment).Utilising the peak rms horizontal(u) values,the critical Shields parameter,θ_c,was calculated and a trend similar to the well-established Shields curve was developed.The analysis was extended to the Shields curve obtained based on the critical shear velocity,Reynolds shear stress,and data extracted fro m the oscillating grid-turbulence experiments.Results show that turbulent fluctuations are crucial for the incipient sediment motion and are essentially better predictors than the commonly used critical shear velocity.A quadrant analysis to identify the role of turbulent bursting events in incipient sediment motion also was done where sweeps and ejections are dominant for finer and coarser sediment sizes,respectively. 相似文献
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Jinlin Li Xiubin He Jie Wei Yuhai Bao Qiang Tang Jean de Dieu Nambajimana Gratien Nsabimana Dil Khurram 《国际泥沙研究》2021,36(4):489-500
The Three Gorges Reservoir(TGR)in China is the largest hydroelectric project in the world,but the threat of sediment affecting ecological sustainability of the reservoir is a topic of concern.Sediment particlesize distribution(PSD)is informative in understanding sediment transport dynamics and biochemical functions.It is,therefore,important to quantitatively characterize the distribution of sediment particles.In the current study,fractal theory is applied to determine the PSD of suspended sediment in the TGR.The results show that the volumetric fractal dimension(D_v)exhibits a significant seasonal difference(p<0.05),reflecting sediment source and hydrodynamic sorting control the granularity of suspended sediment in the TGR.More specifically,suspended sediment particles are coarser in the wet season than in the dry season for the Yangtze River,and the opposite is true for the Ruxi River,an important tributary.The generalized dimension spectrum,D(q)-q,and multifractal singularity spectrum,f[α(q)]-α(q),were calculated for each suspended sediment sample.Thereafter,the parameters,D(0),D(1),D(2),α(0),Δα(q),andΔf[α(q)],were determined to characterize the PSD.As a result,the coarser suspended sediment during the wet season is characterised by a more complex PSD pattern,with a wider range of particle sizes,greater heterogeneity,and greater homogeneity of distribution over the measurement interval.However,the multifractal structure of the PSD of suspended sediment is more complex during the dry season than during the wet season,with higher local dispersion and variability.The findings of the current study highlight that multifractal analysis provides important insight for understanding the PSD of suspended sediment in the TGR. 相似文献
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