吉井

The water level of the irrigation and drainage canal was observed using the water level indicator in the 6ha paddy fields which is selected as the study site and located in the Ohishi diversion weir command area along the Chikugo River. The characteristic of water management in paddy field concerning the weather or growth stage of rice could be clear using the result of the observation. The variation of the water requirement rate depending on the growth stage of the rice or the location of the field could be estimated. The tank model of the paddy field was introduced in the study site. The method of Shuffled Complex Evolution Algorithm (SCE-UA) which is one of the global optimization method was adopted for the tank model parameter estimation. The advantage of this method is that algorithm is relatively easy, the local optimum value can be avoided and it is independent of the initial value. The effectiveness of the SCE-UA method for the parameter identification was proved in this study. The calculated value under the precipitation had good agreement with the observed data, but the calculation in the sunny days didn't fit the observation. There are errors between calculated and observed values under the condition of the manual operation for the water intake. The water level of the paddy field was simulated assuming the future change of water intake in the study site. According to the result of simulation, it proved that it would be difficult that water level of the paddy fields is maintained under the condition of the present water intake of 80%. The present water intake is appropriate in the study site and it is probable that much water intake would be necessary in case of the future decrease and aging of farmworkers.