Study on the Actual and Optimum Water Use in Ohishi Diversion Weir Command Area (2）

The farmworkers in Yoshii-town which is located in Fukuoka prefecture are decreasing and aging gradually. The ratio of part-time farm households having more nonfarm income than agricultural income is increasing. As a result, the rationalization of the farm work would be needed. The control of water intake in the paddy field was reversibly estimated from the observation of water intake using the water level indicator in 600ha study site of Yoshii-town. The estimation could describe the change of the water management with the weather. The calculation using model including the reverse estimation had good agreement with the observation and it proved that this model is effective. According to the simulation using the model, the amount of water intake would be reasonable under condition that the present water management would be maintained. However, Much water intake would be necessary if the water management is rationalized.（1）福岡県朝倉郡吉井町における就農状況は，年々少人数化・高齢化が進んできている．また全農家に対する2種兼業農家の占める割合が増加してきている．その結果，今後農作業の合理化が求められることが予想される．（2）対象地区において行なった自記水位計を用いた取水実態をもとに，当地区における水田水操作の逆推定を試みた．逆推定結果を検証したところ，1日単位での用水操作をうまく再現することができた．（3）逆推定結果を組み込んだモデルによる計算結果は実測値と良い一致を示しており，本モデルの妥当性が実証された．モデルを用いて行なったシミュレーション結果から当地区では現状の管理状態ならば適切な取水が行なわれていると判断できた．しかし，今後用水管理の粗放化，合理化が進んだ場合は，多量の用水もしくは現状の管理状態を維持することのできる設備が必要になると思われる