Abstract:An increasing impervious area is quickly extending over the Wu-Tu watershed due to the endless demands of the people. Generally, impervious paving is a major result of urbanization and more recently has had the potential to produce more enormous flood disasters than those of the past. In this study, 40 available rainfall-runoff events were chosen to calibrate the applicable parameters of the models and to determine the relationships between the impervious surfaces and the calibrated parameters. Model inputs came from the outcomes of the block kriging method and the non-linear programming method. In the optimal process, the shuffled complex evolution method and three criteria were applied to compare the observed and simulated hydrographs. The tendencies of the variations of the parameters with their corresponding imperviousness were established through regression analysis. Ten cases were used to examine the established equations of the parameters and impervious covers. Finally, the design flood routines of various return periods were furnished through use of approaches containing a design storm, block kriging, the SCS model, and a rainfall-runoff model with established functional relationships. These simulated flood hydrographs were used to compare and understand the past, present, and future hydrological conditions of the watershed studied. In the research results, the time to peak of flood hydrographs for various storms was diminished approximately from 11 h to 6 h in different decrements, whereas peak flow increased respectively from 127 m 3 s 1 to 629 m 3 s 1 for different storm intensities. In addition, this study provides a design diagram for the peak flow ratio to help engineers and designers to construct hydraulic structures efficiently and prevent possible damage to human life and property.

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This study mainly explores effects of urbanization factors on hydrograph parameters. Urbanization impacts of the developing watershed are evaluated based on rainfall-runoff simulations. A total of 51 rainfall-runoff events occurred from 1966 to 2002. Forty of these were calibrated, and effects of urbanization factors on runoff hydrographs resulting from a simple hydrological model were assessed. The block Kriging method was used to estimate the mean rainfall of the Wu-Tu watershed, and its hourly excesses were calculated by using the non-linear programming method. The remaining 11 cases were used to test the established relationships. The calibration and verification results confirm that the integral methods used in this study effectively illustrate the hydrological and geomorphic conditions in complex urbanization processes. Parameter n responds more sensitively than parameter k to increasing impervious areas and population densities. Additionally, parameter n responds more strongly to imperviousness than to population. Therefore, an impervious area is an important reference for analyzing hydrological changes of urbanization in the Wu-Tu watershed.

This study examines relationships between model parameters and urbanization variables for evaluating urbanization effects in a watershed. Rainfall-runoff simulation using the Nash model is the main basis of the study. Mean rainfall and excesses resulting from time-variant losses were completed using the kriging and nonlinear programming methods, respectively. Calibrated parameters of 47 events were related to urbanized variables, change of shape parameter responds more sensitively than that of scale parameter based on comparisons between annual average and optimal interval methods. Regression equations were used to obtain four continuous correlations for linking shape parameter with urbanization variables. Verification of 10 events demonstrates that shape parameter responds more strongly to imperviousness than to population, and a power relationship is suitable. Therefore, an imperviousness variable is a major reference for analysing urbanization changes to a watershed. This study found that time to peak of IUH was reduced from 11.76 to 3.97 h, whereas peak discharge increased from 44.79 to 74.92 m 3 /s. Identification des paramètres d'un hydrogramme et leurs relations aux variables d'urbanisationRésumé Cette étude examine les relations entre les paramètres d'un modèle et des variables d'urbanisation afin d'évaluer les effets de l'urbanisation dans un bassin versant. La simulation pluie-débit utilisant le modèle de Nash est la principale base de l'étude. La pluviométrie moyenne et les surplus résultant de pertes variant au cours du temps ont été estimés en utilisant respectivement le krigeage et la programmation non linéaire. Les paramètres calés de 47 événements ont été reliés à des variables d'urbanisation, les changements du paramètre de forme étant plus sensibles que ceux du paramètre d'échelle sur la base des comparaisons entre les moyennes annuelles et des méthodes d'intervalle optimum. Des équations de régression ont été utilisées pour obtenir quatre corrélations continues reliant le paramètre de forme avec les variables d'urbanisation. La vérification sur 10 événements démontre que le paramètre de forme réagit plus fortement à l'imperméabilisation qu'à la population, et une relation en puissance est appropriée. Par conséquent, une variable d'imperméabilisation constitue une référence majeure pour l'analyse des changements dus à l'urbanisation d'un bassin versant. Cette étude a révélé que le temps de montée de l'hydrogramme unitaire instantané a été réduit de 11.76 à 3.97 h, alors que le débit de pointe a augmenté de 44.79 à 74.92 m 3 /s.

This study investigates the shape characteristics of hydrograph components of the Wu-Tu watershed in Taiwan based on observations of rainfall and streamflow. Component hydrographs were modeled using a model of three serial tanks with one parallel tank. The block kriging method was used to calculate the hourly mean rainfall of events, and eight model parameters of 34 cases were derived from the shuffled complex evolution optimal algorithm. The remaining 18 events were used to verify the applicability of the calibrated parameters. Results show that (1) times to peak of hydrograph components are positively nonlinearly correlated to peak time of rainfall; (2) peak discharges of hydrograph components are linearly proportional to those of streamflow hydrograph; and (3) relationships of total discharges also have direct ratios between hydrograph components and observed streamflow. Using the procedures proposed in this study, three evaluated shape characteristics of component hydrographs can be easily used to rapidly determine shapes of simple hydrographs.

Rainfall analysis is important to managing water resources. Mean rainfall is usually used to calculate the spatial rainfall status of a region and is the input into various rainfall-runoff models. However, this method relies on an adequate raingauge network. This study identifies the effects of raingauge distribution based on estimation results of areal rainfall using the Thiessen polygon and block Kriging methods. Twelve rainfall events with complete data from 14 raingauges were selected to complete the goal of this study. The block Kriging method in this study uses a dimensionless semivariogram to obtain hourly semivariograms based on a standardized rainfall depth. The power semivariogram model was used to describe the temporal-spatial variation of rainfall. The analytical process in this study uses raingauge weight and rainfall volume as evaluation criteria. All raingauges were in turn removed from the original raingauge network. The effects of removing each raingauge were compared with computations using all raingauges. Comparison results indicate that (1) the block Kriging method can accurately describe rainfall processes in terms of the spatiotemporal structure of a semivariogram. (2) the block Kriging method is better than the Thiessen polygon method at obtaining exact mean rainfall, and (3) the effects of different raingauge distributions on a mean hyetograph warrant further investigation.

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