Due to the occurrence of ponding during the period of rice growth, the analyses of rainfall-runoff in paddy fields are different from those in general lands. The diffusive tank model has been successfully applied in rainfall-runoff simulations in paddy fields because it can well describe the features of the local water flow. In most of the applications of this model, although the determination of the related model parameters is important, detailed investigations on each individual parameter are definitely needed to improve the accuracy of the results. In the study, an improved procedure is proposed to determine certain variables involved in the diffusive tank model and the application is conducted in a field area in Taiwan. In the application, the roughness of the river channel was assessed according to the actual field conditions. Instead of using the observed water levels in each rainfall event, the notch width of the rectangular contracted weir per unit area was evaluated by direct field measurements to calibrate the discharge coefficient. Test results from the selected field in six rainfall events showed that the local average value of the notch width of the rectangular contracted weir per unit area was 1.025 m/ha. Compared to the results of field measurements, the relative errors of the predictions were within 3% in all tests of rainfall events. In addition, for different types of catchment partitions, it was found that the corresponding weir discharge coefficients remained roughly unchanged. Copyright (C) 2003 John Wiley Sons, Ltd

Many automatic calibration processes have been proposed to efficiently calibrate the 16 parameters involved in the fourlayered tank model. The Multistart Powell and Stuffed Complex Evolution (SCE) methods are considered the best two procedures. Two rainfall events were designed to compare the performance and efficiency of these two methods. The first rainfall event is short term and the second designed for long term rainfall data collection. Both rainfall events include a lengthy no-rainfall period. Two sets of upper and lower values for the search range were selected for the numerical tests. The results show that the Multistart Powell and SCE methods are able to obtain the true values for the 16 parameters with a sufficiently long no-rainfall period after a rainfall event. In addition, by using two selected objective functions, one based on root mean square error and one based on root mean square relative error criteria, it is found that the no-rainfall period lengths necessary to obtain the converged true values for the 16 parameters are roughly the same. The SCE method provides a more efficient search based on an appropriate preliminary search range. The Multistart Powell method, on the other hand, leads to more accurate search results when there is no suitable search range selected based on the parameter calibration experience. (KEY TERMS: surface water hydrology; rainfall/runoff modeling; tank model; parameter estimation; Multistart Powell method; SCE method.)

Terraced paddy fields play a crucial role in water and soil conservation because their water-storage capacity reduces flood peaks in mountainous areas. The water-storage capacity of a paddy field is mainly dependent on the size of the field, the height of the bund, and the outlet within the bund. However, the height of the bund and outlet can be reduced due to a lack of maintenance, especially when rice paddies have been abandoned. This study assessed the flood-control function of a terraced paddy field during heavy-rainfall events. The four-layered tank model calibrated by in situ rainfall-runoff measurements was applied to determine the effects of reducing the height of the bund and the outlet within the bund, on the drainage peak flow of terraced fields. The simulation results from two heavy-rainfall events indicated the excellent flood-control function of terraced paddy fields. The simulation results showed that the drainage peak flow underwent considerable changes when the height of the bund and outlet was reduced by more than 50%. Therefore, sustainable rice planting in the terraced paddies or maintenance of the water-storage capability in abandoned arable land is necessary to release downstream flood pressure.

Terraced paddy fields play important roles in water and soil conservation because their water storage effect reduces and delays flood peaks. This study applies the terraced paddy field rainfall-runoff mechanism to the tank model. Though the traditional four-section tank model can easily simulate rainfall-runoff in a terraced paddy field, it has many parameters that are difficult to calibrate. To address the shortcomings of the traditional four-section tank model, this study develops a revised tank model to simulate rainfall-runoff. This study selects a terraced paddy field located in Hsuing-Pu village in Hsiuing-Chu County as the experimental field. The field under investigation was equipped with automatic monitoring stations, water-stage, and rain gauges. These stations collected data on rainfall and water flow to simulate the rainfall-runoff model in that region. To simulate the runoff behavior of the experimental terraced paddy field, two rainfall events were selected from the gathered data and five normal evaluation indexes based on static and hydrological theory were applied to calculate the results of simulation simultaneously. The revised tank model performed better than expected, and precisely predicted the variations and trends in flow charge. Comparison with representation indexes proved that the revised tank model is an appropriate and valuable tool for rainfall-runoff simulation

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.