Browsing by Author "ZHAO, B"

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DETERMINATION OF UNIT HYDROGRAPHS BY MULTIPLE STORM ANALYSIS
(1994-12-01)
ZHAO, B
;
TUNG, YK
;
YANG, JC
;
土木工程學系
;
Department of Civil Engineering
This paper discusses the derivation of a unit hydrograph by multiple storm analysis using least squares methods. Variations of least squares method was generalized using the framework of weighted ridge analysis. The paper also shows two theorems to support using multi-storm analysis to derive UH. In addition, an issue was addressed on the scaling effect in the conventional multi-storm analysis which could create potential bias toward large storms in deriving a multi-storm UH. For that, a simple scaling procedure was proposed to reduce such potential bias problem. Numerical investigations were conducted to examine the performance of the scaling procedure by comparing with the conventional multi-storm analysis (without scaling) and the HEC-1 weighing procedures. Based on various performance criteria using a total of 39 storms from three watersheds, the proposed scaling procedure was found to produce a quite desirable UH.
ESTIMATION OF UNIT-HYDROGRAPH BY RIDGE LEAST-SQUARES METHOD
(1995-05-01)
ZHAO, B
;
TUNG, YK
;
YANG, JC
;
土木工程學系
;
Department of Civil Engineering
Least squares (LS) methods are frequently used to determine an optimal unit hydrograph (UH) for a watershed. However, the conventionally used ordinary LS method could potentially produce a UH with unwanted fluctuation among hydrograph ordinates. When that occurs, the ridge LS method can be used to reduce noise fluctuation in a derived UH. In the framework of the ridge LS method, a UH can be obtained by minimizing the mean-squared error (MSE) of the estimated UH or direct runoff hydrograph (DRH). Therefore, the ridge LS method theoretically would enhance the predictability of the derived UH. This paper describes methodologies of obtaining the optimal ridge parameter for use in the ridge LS method to estimate a UH. Furthermore, the unit volume constraint is considered in the determination of the optimal ridge parameter. A statistical validation study is also conducted to show that a UH obtained by the ridge LS method has a better predictive capability than the one derived by the ordinary LS method.
STATISTICAL VALIDATION METHODS - APPLICATION TO UNIT HYDROGRAPHS
(1995-08-01)
ZHAO, B
;
TUNG, YK
;
YEH, KC
;
YANG, JC
;
土木工程學系
In hydraulic and hydrologic studies, engineers develop new models or calibrate existing models by various techniques. One is often concerned with the model validity regarding its ability to predict future events. Five potentially useful statistical validation methods are presented. For illustration, they were applied to examine the predictability of unit hydrographs derived by various methods in the framework of the least squares and its variations. It was found that storm-stacking (conventional multistorm analysis) together with storm-scaling yields the most desirable UH, The general framework of these validation methods can also be applied to a validation study of other hydrologic and hydraulic models.