棚田地区における圃場整備後の田面および溜池の水管理 A Case Study of the Water Management of Paddy Field and Irrigation Pond after Farmland Consolidation in the Terraced Paddy Field Area
石川県と富山県にまたがる棚田地域において圃場整備が実施され, 生産基盤が大きく改善された. 本報告は, 整備後における水管理状況について調査し, 検討を加えたものである. 調査の結果, 整備前から利水に不便な受益者は, 整備後も整備前と同様の田面の水管理を行っており, 利水状況が改善されたと判断するまで3年近く要している. 水源である溜池の管理労力は, 整備前と変わらず一日中時間が拘束される過酷な状況にあり, 貯水率が中干し開始時 (6月中旬) までに50%以下になると危機的状況になる. 梅雨期に満水を確保するには, 灌漑開始から梅雨期までに約700mmの降雨が必要であり, これは, 4年確率に相当している. 以上のように, 圃場整備が実施されたとはいえ, 溜池管理労力, 水資源の確保等に多大の労力を払っていることが明らかとなった.
Farmland consolidation was carried out in the terrace paddy field areas in Ishikawa prefecture, and the production basis was greatly improved. Water management investigation was carried out in this region, and the situation after the improvement was examined. The results obtained are as follows: 1) Almost three years were needed after the farmland consolidation for all beneficiaries to have a confirmation that the consolidation had improved the conditions of water utilization. In 1999, the total water supply for the paddy field during the irrigation season was 910mm, 46% of which was from irrigation ponds and 54% from rainfall. The ratio of available rainfall was 77%. 2) Irrigation pond managers carried out supply management following the standard measurement of supply discharge indicated by the levels of the storage set for each Irrigation pond. They had to watch the timing of optimal supply discharges for 24 hours, which was as hard a labor as had been required before the consolidation. 3) The storage rate of the irrigation pond kept decreasing from the start of irrigation. A critical phase would be caused if the storage rate went down to 50% or less by the middle of June (the beginning of intermediate drainage from the paddy field). In order for irrigation ponds to be filled and to maintain storage discharge after the intermediate drainage, the simulation result indicated that about 700mm of rainfall, which corresponds to a period of four return years, would be needed from the beginning of irrigation until the end of the rainy season.
農業土木学会論文集 69(6), 799-805, 2001-12-25
The Japanese Society of Irrigation, Drainage and Rural Engineering