Abstract:This study focuses mainly on observing urban development in Taiwan's Wu-Tu watershed from the perspective of urban hydrological theory. An approach is proposed for developing a method for incorporating available meteorological data to define the degree of change in a runoff hydrograph for urbanizing basins. The mean rainfall was estimated using the Kriging method. For calibration, two methods of calculating the effective rainfall (the -index method and the non-linear-programming (NLP) method) were used as model inputs, and the optimal global parameters of the linear reservoir model were then obtained from the shuffled complex evolution (SCE) algorithm. Twenty-six (1966Twenty-six ( -1991 and eight (1994)(1995)(1996)(1997) rainfall-runoff events were used for calibration and verification, respectively. The NLP method yielded better results than the -index method, especially for multipeak rainfall-runoff events. The regression equation determined the relationship between the parameters of the model and impervious areas. A comparison based on the results of the instantaneous unit hydrograph of the study area revealed that three decades of urbanization had increased the peak flow by 27%, and the time to peak was decreased by 4 h. The study simply describes the results of the impact of imperviousness on hydrological modelling.

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.

Abstract:Taiwan suffers from heavy storm rainfall during the typhoon season. This usually causes large river runoff, overland flow, erosion, landslides, debris flows, loss of power, etc. In order to evaluate storm impacts on the downstream basin, a real-time hydrological modelling is used to estimate potential hazard areas. This can be used as a decision-support system for the Emergency Response Center, National Fire Agency Ministry, to make 'real-time' responses and minimize possible damage to human life and property. This study used 34 observed events from 14 telemetered rain-gauges in the Tamshui River basin, Taiwan, to study the spatial-temporal characteristics of typhoon rainfall. In the study, regionalized theory and cross-semivariograms were used to identify the spatial-temporal structure of typhoon rainfall. The power form and parameters of the cross-semi-variogram were derived through analysis of the observed data. In the end, cross-validation was used to evaluate the performance of the interpolated rainfall on the river basin. The results show the derived rainfall interpolator represents the observed events well, which indicates the rainfall interpolator can be used as a spatial-temporal rainfall input for real-time hydrological modelling.

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An impervious surface cover is continuously spreading over the Wu-Tu upstream watershed due to the concentrated population and raised economical demands, while that area also frequently suffers from heavy storms or typhoons during the summer season. The increased flood volume due to this extended imperviousness causes a greater potential hazard than that of the past. In order to evaluate the urbanized impacts on the watershed, a set of methods were used to estimate the changes of the watershed storage. This research chose 51 observed events from three raingauges on the Wu-Tu upstream watershed, Taiwan, to study the volume characteristic of abstracted rainwater. In the study, the block Kriging method was used to estimate the area rainfall and the hourly excess was derived through the non-linear programing (NLP). A total of 40 samples were calibrated through the hydrological model and the Soil Conservation Service (SCS) model using the optimum seeking method in order to search out and establish the best parameters that illustrate the hydrological and geomorphic conditions at that time. Eleven cases were used to examine the established relationship of the parameters and the impervious coverings. A design storm approach was used to view the changes of the volume for various scale storms/typhoons because of the different degrees of urbanization. Then, a diagram was designed to show the relationships that exist among the runoff coefficient, return period, and impervious surface. The satisfactory results show that storage capability of rainwater for various scale storms on the Wu-Tu watershed would be respectively reduced about 42-156 cms in different decrements up to now.

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.

A semi-distributed model with a parallel connection was applied to examine the effects of urbanization variables. Data were obtained from watershed divisions that were characterized by various degrees of urbanization. The mean rainfall was calculated using the kriging method. The model inputs were obtained by subtracting mean rainfall from Ф-index values, based on the spatially uniform loss assumption. Regression analysis was applied to determine the relationship between the parameters of 64 calibrations and urbanization variables among the divisions. The results showed that overland parameters produced more consistent change in response to imperviousness than to population. Conversely, the channel parameter was unaffected by changes in urbanization. The verification results of 46 cases showed that power linkage was a potential option for linking division parameters with the corresponding imperviousness based on four evaluation criteria. The changes in imperviousness on overland parameters show the hydrological effects of division urbanizations.

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.