It is important to have a reasonable estimation of sediment transport rate with respect to its significant role in the planning and management of water resources projects. The complicate nature of sediment transport i...It is important to have a reasonable estimation of sediment transport rate with respect to its significant role in the planning and management of water resources projects. The complicate nature of sediment transport in gravel-bed rivers causes inaccuracies of empirical formulas in the prediction of this phenomenon. Artificial intelligences as alternative approaches can provide solutions to such complex problems. The present study aimed at investigating the capability of kernel-based approaches in predicting total sediment loads and identification of influential parameters of total sediment transport. For this purpose, Gaussian process regression(GPR), Support vector machine(SVM) and kernel extreme learning machine(KELM) are applied to enhance the prediction level of total sediment loads in 19 mountain gravel-bed streams and rivers located in the United States. Several parameters based on two scenarios are investigated and consecutive predicted results are compared with some well-known formulas. Scenario 1 considers only hydraulic characteristics and on the other side, the second scenario was formed using hydraulic and sediment properties. The obtained results reveal that using the parameters of hydraulic conditions asinputs gives a good estimation of total sediment loads. Furthermore, it was revealed that KELM method with input parameters of Froude number(Fr), ratio of average velocity(V) to shear velocity(U*) and shields number(θ) yields a correlation coefficient(R) of 0.951, a Nash-Sutcliffe efficiency(NSE) of 0.903 and root mean squared error(RMSE) of 0.021 and indicates superior results compared with other methods. Performing sensitivity analysis showed that the ratio of average velocity to shear flow velocity and the Froude number are the most effective parameters in predicting total sediment loads of gravel-bed rivers.展开更多
Based on the research into the physical-chemical properties and distribution of sediments and the characteristics of pore water in sediments of Miyun reservoir, the release flux of the total phosphorus (TP) from sedim...Based on the research into the physical-chemical properties and distribution of sediments and the characteristics of pore water in sediments of Miyun reservoir, the release flux of the total phosphorus (TP) from sediments is estimated by simulating deposit environment of reservoir bottom in laboratory. They are 0.018 mg·cm-2·d-1 and 0.821 mg·cm-2·d-1 at 2℃ and 8℃ respectively. The gross TP released in a year is 11.34t. As a contrast, the pore water diffusion simulation method is used to measure gross TP released and gains 11.56t. The two results are relatively close and prove that experiment simulation has some reliability. On the basis of experiments, some conclusions can be drawn: (1) Endogenous phosphorus from sediments accounts for 27.9 percent of the TP entering the reservoir, and it cannot be ignored; and (2) increasing temperature is helpful to TP releasing from sediments.展开更多
The morphological changing trend of the Yangtze Estuary,the largest estuary of Asia,has become a focus of research in recent years.Based on a long series of topographic data from 1950 to 2015,this paper studied the er...The morphological changing trend of the Yangtze Estuary,the largest estuary of Asia,has become a focus of research in recent years.Based on a long series of topographic data from 1950 to 2015,this paper studied the erosion-deposition pattern of the entire Yangtze Estuary.An alternation between erosion and deposition was found during the past 65 years,which was in correspondence to the alternation between flood and dry periods identified by multi-year average duration days of high-level water flow(defined as discharge≥60,000 m 3/s,namely,D≥60,000)from the Yangtze River Basin.A quantitative relationship was further developed between the erosional/depositional rate of the Yangtze Estuary and the interpreting variables of yearly water discharge,D≥60,000 and yearly river sediment load,with contributing rates of 1%,59%and 40%,respectively.Mechanism behind the alternate erosion and deposition pattern was analyzed by examining residual water surface slope and the corresponding capacity of sediment transport in flood and dry periods.In flood periods,a larger discharge results in steeper slope of residual water level which permits a greater capacity of sediment transport.Therefore,more bed materials can be washed to the sea,leading to erosion of the estuary.In contrast,flatter slope of residual water level occurs in dry periods,and deposition dominates the estuarine area due to the decreased capacity of sediment transport and the increased backwater effect of flood-tide.Coastal dynamics and estuarine engineering projects alter the local morphological changes,but slightly affect the total erosional/depositional rate of the whole estuarine region.Heavy sedimentation within the Yangtze Estuary after the impoundment of the Three Gorges Dam can be attributed to the reduced occurrence frequency of flood years due to water regulation by the dam,and largely(at least 36%-52%)sourced from the sea.Deposition is still possible to occur in the Yangtze Estuary in the future,because the multi-year average D≥60,000 is unlikely to exceed the critical value of 14 days/yr which corresponds to the future equilibrium state of the Yangtze Estuary,under the water regulation of the large cascade dams in the upper Yangtze.Nevertheless,the mean depositional rate will not surpass the peak value of the past years,since the total sediment load entering the Yangtze Estuary has presented a decreasing trend.展开更多
文摘It is important to have a reasonable estimation of sediment transport rate with respect to its significant role in the planning and management of water resources projects. The complicate nature of sediment transport in gravel-bed rivers causes inaccuracies of empirical formulas in the prediction of this phenomenon. Artificial intelligences as alternative approaches can provide solutions to such complex problems. The present study aimed at investigating the capability of kernel-based approaches in predicting total sediment loads and identification of influential parameters of total sediment transport. For this purpose, Gaussian process regression(GPR), Support vector machine(SVM) and kernel extreme learning machine(KELM) are applied to enhance the prediction level of total sediment loads in 19 mountain gravel-bed streams and rivers located in the United States. Several parameters based on two scenarios are investigated and consecutive predicted results are compared with some well-known formulas. Scenario 1 considers only hydraulic characteristics and on the other side, the second scenario was formed using hydraulic and sediment properties. The obtained results reveal that using the parameters of hydraulic conditions asinputs gives a good estimation of total sediment loads. Furthermore, it was revealed that KELM method with input parameters of Froude number(Fr), ratio of average velocity(V) to shear velocity(U*) and shields number(θ) yields a correlation coefficient(R) of 0.951, a Nash-Sutcliffe efficiency(NSE) of 0.903 and root mean squared error(RMSE) of 0.021 and indicates superior results compared with other methods. Performing sensitivity analysis showed that the ratio of average velocity to shear flow velocity and the Froude number are the most effective parameters in predicting total sediment loads of gravel-bed rivers.
文摘Based on the research into the physical-chemical properties and distribution of sediments and the characteristics of pore water in sediments of Miyun reservoir, the release flux of the total phosphorus (TP) from sediments is estimated by simulating deposit environment of reservoir bottom in laboratory. They are 0.018 mg·cm-2·d-1 and 0.821 mg·cm-2·d-1 at 2℃ and 8℃ respectively. The gross TP released in a year is 11.34t. As a contrast, the pore water diffusion simulation method is used to measure gross TP released and gains 11.56t. The two results are relatively close and prove that experiment simulation has some reliability. On the basis of experiments, some conclusions can be drawn: (1) Endogenous phosphorus from sediments accounts for 27.9 percent of the TP entering the reservoir, and it cannot be ignored; and (2) increasing temperature is helpful to TP releasing from sediments.
基金Youth Project of National Natural Science Foundation of China,No.41601275Open Research Fund of Key Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province,No.2019SS06Scientific Research Key Project in Hunan Province Education Department,No.2014A006。
文摘The morphological changing trend of the Yangtze Estuary,the largest estuary of Asia,has become a focus of research in recent years.Based on a long series of topographic data from 1950 to 2015,this paper studied the erosion-deposition pattern of the entire Yangtze Estuary.An alternation between erosion and deposition was found during the past 65 years,which was in correspondence to the alternation between flood and dry periods identified by multi-year average duration days of high-level water flow(defined as discharge≥60,000 m 3/s,namely,D≥60,000)from the Yangtze River Basin.A quantitative relationship was further developed between the erosional/depositional rate of the Yangtze Estuary and the interpreting variables of yearly water discharge,D≥60,000 and yearly river sediment load,with contributing rates of 1%,59%and 40%,respectively.Mechanism behind the alternate erosion and deposition pattern was analyzed by examining residual water surface slope and the corresponding capacity of sediment transport in flood and dry periods.In flood periods,a larger discharge results in steeper slope of residual water level which permits a greater capacity of sediment transport.Therefore,more bed materials can be washed to the sea,leading to erosion of the estuary.In contrast,flatter slope of residual water level occurs in dry periods,and deposition dominates the estuarine area due to the decreased capacity of sediment transport and the increased backwater effect of flood-tide.Coastal dynamics and estuarine engineering projects alter the local morphological changes,but slightly affect the total erosional/depositional rate of the whole estuarine region.Heavy sedimentation within the Yangtze Estuary after the impoundment of the Three Gorges Dam can be attributed to the reduced occurrence frequency of flood years due to water regulation by the dam,and largely(at least 36%-52%)sourced from the sea.Deposition is still possible to occur in the Yangtze Estuary in the future,because the multi-year average D≥60,000 is unlikely to exceed the critical value of 14 days/yr which corresponds to the future equilibrium state of the Yangtze Estuary,under the water regulation of the large cascade dams in the upper Yangtze.Nevertheless,the mean depositional rate will not surpass the peak value of the past years,since the total sediment load entering the Yangtze Estuary has presented a decreasing trend.
