Browsing by Author "Tung, YK"

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Identification and stochastic generation of representative rainfall temporal patterns in Hong Kong territory
(2006-04-01)
Wu, SJ
;
Yang, JC
;
Tung, YK
;
土木工程學系
;
Department of Civil Engineering
In hydrosystem engineering design and analysis, temporal pattern for rainfall events of interest is often required. In this paper, statistical cluster analysis of dimensionless rainfall pattern is applied to identify representative temporal rainfall patterns typically occurred in Hong Kong Territory. For purpose of selecting an appropriate rainfall pattern in engineering applications, factors affecting the occurrence of different rainfall patterns are examined by statistical contingency tables analysis through which the inter-dependence of the occurrence frequency of rainfall patterns with respect to geographical location, rainfall duration and depth, and seasonality is investigated. Furthermore, due to inherent variability of rainfall mass curves or hyetographs within each classified rainfall pattern, a practical procedure to probabilistically generate plausible rainfall patterns is described. The procedure preserves the inherent stochastic features of random dimensionless rainfall hyetograph ordinates, which in general are correlated non-normal multivariate compositional variables.
Method for performance evaluation of hydrologic and hydraulic models
(1996)
Yang, JC
;
Yeh, KC
;
Tung, YK
;
土木工程學系
;
Department of Civil Engineering
Regionalization of unit hydrograph parameters .1. Comparison of regression analysis techniques
(1997-04-01)
Tung, YK
;
Yeh, KC
;
Yang, JC
;
土木工程學系
;
Department of Civil Engineering
Hydrologic regionalization is a useful tool that allows for the transfer of hydrological information from gaged sites to ungaged sites. This study developed regional regression equations that relate the two parameters in Nash's IUH model to the basin characteristics for 42 major watersheds in Taiwan. In the process of developing the regional equations, different regression procedures including the conventional univariate regression, multivariate regression, and seemingly unrelated regression were used. Multivariate regression and seeming unrelated regression were applied because there exists a rather strong correlation between the Nash's IUH parameters. Furthermore, a validation study was conducted to examine the predictability of regional equations derived by different regression procedures. The study indicates that hydrologic regionalization involving several dependent variables should consider their correlations in the process of establishing the regional equations. The consideration of such correlation will enhance the predictability of resulting regional equations as compared with the ones from the conventional univariate regression procedure.
Regionalization of unit hydrograph parameters .2. Uncertainty analysis
(1997-04-01)
Yeh, KC
;
Yang, JC
;
Tung, YK
;
土木工程學系
;
Department of Civil Engineering
Hydrologic model parameters obtained from regional regression equations are subject to uncertainty. Consequently, hydrologic model outputs based on the stochastic parameters are random. This paper presents a systematic analysis of uncertainty associated with the two parameters, N and K, in Nash's IUH model from different regional regression equations. The uncertainty features associated with N and K are further incorporated to assess the uncertainty of the resulting IUH. Numerical results indicate that uncertainty of N and K from the regional regression equations are too significant to be ignored.
Reliability analysis of hydraulic structures considering unit hydrograph uncertainty
(1997-02-01)
Zhao, B
;
Tung, YK
;
Yeh, KC
;
Yang, JC
;
土木工程學系
Unit hydrographs (UHs), along with design rainfalls, are frequently used to determine the discharge hydrograph for design and evaluation of hydraulic structures. Due to the presence of various uncertainties in its derivation, the resulting UH is inevitably subject to uncertainty. Consequently, the performance of hydraulic structures under the design storm condition is uncertain. This paper integrates the linearly constrained Monte-Carlo simulation with the UH theory and routing techniques to evaluate the reliability of hydraulic structures. The linear constraint is considered because the water volume of each generated design direct runoff hydrograph should be equal to that of the design effective rainfall hyetograph or the water volume of each generated UH must be equal to one inch (or cm) over the watershed. For illustration, the proposed methodology is applied tb evaluate the overtopping risk of a hypothetical flood detention reservoir downstream of Tong-Tou watershed in Taiwan.
Risk analysis of reservoir level during rehabilitation
(2000)
Wu, SJ
;
Yang, JC
;
Tung, YK
;
土木工程學系
;
Department of Civil Engineering
After five decades of service since 1953, the storage capacity of Ah-gong-dein reservoir in Taiwan has been reduced by about 71% due to accumulated sedimentation. Its ability to serve flood control function has been greatly compromised. The Taiwan Department of Water Resources currently is undertaking measures to vitalize its flood control function over an eight-year period. The paper addresses probabilistic behavior of reservoir surface level during the rehabilitation period. In particular, randomness of monthly rainfall amounts is considered in developing function relationship between monthly probability of water surface elevation exceeding certain target level and various factors. Information such as these is useful to examine the implications of proposed rehabilitation schemes on overtopping risk and to monitor the required revitalization progress and reservoir storage condition.
Storm resampling for uncertainty analysis of a multiple-storm unit hydrograph
(1997-07-01)
Zhao, B
;
Tung, YK
;
Yeh, KC
;
Yang, JC
;
土木工程學系
Due to various types of uncertainties involved in the estimation of a unit hydrograph (UH), the UH derived by any method is subject to uncertainties. Based on the concept of the bootstrap resampling technique, a practical methodology called storm resampling is proposed to quantify the uncertainties of multiple-storm UH ordinates and any parameters involved in the estimation of the multiple-storm UH. The important UH ordinates and parameters may include UH peak discharge, UH time-to-peak, UH volume, condition number related to the effective rainfall matrix, mean square error of the UH, and ridge parameter. The proposed bootstrap-based storm resampling technique, along with the least squares and ridge least squares solution techniques, is applied to typhoon storm events over a watershed in Taiwan. The methodology can be applied to other UH solution techniques and other hydrological and hydraulic simulation/optimization models. (C) 1997 Elsevier Science B.V.
Storm resampling for uncertainty analysis of a multiple-storm unit hydrograph
(1997-07-01)
Zhao, B
;
Tung, YK
;
Yeh, KC
;
Yang, JC
;
土木工程學系
Due to various types of uncertainties involved in the estimation of a unit hydrograph (UH), the UH derived by any method is subject to uncertainties. Based on the concept of the bootstrap resampling technique, a practical methodology called storm resampling is proposed to quantify the uncertainties of multiple-storm UH ordinates and any parameters involved in the estimation of the multiple-storm UH. The important UH ordinates and parameters may include UH peak discharge, UH time-to-peak, UH volume, condition number related to the effective rainfall matrix, mean square error of the UH, and ridge parameter. The proposed bootstrap-based storm resampling technique, along with the least squares and ridge least squares solution techniques, is applied to typhoon storm events over a watershed in Taiwan. The methodology can be applied to other UH solution techniques and other hydrological and hydraulic simulation/optimization models. (C) 1997 Elsevier Science B.V.
Uncertainty analysis by point estimate methods incorporating marginal distributions
(1997-03-01)
Chang, CH
;
Yang, JC
;
Tung, YK
;
土木工程學系
;
Department of Civil Engineering
The model performance of an engineering system is affected by many variables subject to uncertainty. Point estimate (PE) methods are practical tools to assess the uncertainty features of a model involving multivariate stochastic parameters. Two PE methods have been developed for engineering applications. One is Rosenblueth's PE method, which preserves the first three moments of random variables and the other is Harr's PE method, which reduces the computations of Rosenblueth's method but only as appropriate for application to random variables with normal distributions. In this study, two algorithms are proposed to encompass the advantages of the two PE methods: computational practicality and the handling of mixture distributions. Through a numerical experiment, the proposed methods yielded mom accurate estimations than those of Rosenblueth's method with about the same amount of computation as Harr's method. The two proposed methods were also applied to estimate statistical moments of a pier scouring model output to demonstrate their performance in an engineering application.