Abstract
The proper assessment of design flood is a major concern for many hydrological applications in small urban watersheds. A number of approaches can be used including statistical approach and the continuous simulation and design storm methods. However, each method has its own limitations and assumptions being applied to the real world. The design storm method has been widely used for a long time because of the simplicity of the method, but three critical assumptions are made such as the equality of the return periods between the rainfall and corresponding flood quantiles and the selections of the rainfall hyetograph and antecedent soil moisture conditions. Continuous simulation cannot be applied to small urban catchments with quick responses of runoff to rainfall. In this paper, a new flood frequency analysis for the simulated annual peak flows (FASAP) is proposed. This method employs the candidate rainfall events selected by considering a time step order of five minutes and a sliding duration without any assumptions about the conventional design storm method in an urban watershed. In addition, the proposed methodology was verified by comparing the results with the conventional method in a real urban watershed.
Highlights
Evaluating flood frequency and determining the design flood are the final goals for hydrological analysis and the beginning of integrated flood control [1]
Hydrological research on the determination of the design flood for the evaluation of flood frequency can be classified into two approaches: (1) statistical approach estimates flood quantiles by applying probability models to flood data to determine the design flood; and (2) the design storm method uses the rainfall-runoff model and considers the rainfall quantiles determined by frequency analysis as the input data [3]
The proposed method is used to determine the design flood by applying frequency analysis to the simulated annual peak flows obtained from the selected candidate rainfall events that may produce the annual peak flows in the design storm method, unlike the continuous simulation method where all the rainfall series are used
Summary
Evaluating flood frequency and determining the design flood are the final goals for hydrological analysis and the beginning of integrated flood control [1]. The design storm method is used to estimate flood quantiles by applying rainfall quantiles determined from rainfall frequency analysis to the rainfall-runoff model. Because a continuous simulation method using daily rainfall time-series tends to estimate lower peak flow than the actual peak flow [22], this method is not considered a practical method in a small urban watershed where the runoff process is completed within a day [14]. The proposed method can overcome data homogeneity due to the lack of flood data and land use changes commonly encountered in flood frequency analyses This method does not require the three basic assumptions of the design storm method. The proposed FASAP seems to possess high efficiency and accuracy for small urban watersheds while following the procedures of the existing continuous simulation methodology
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