利用蓄水設施提升灌溉機動性

Abstract

台灣近年來因社會經濟及生活形態改變導致專業農戶日漸減少，兼業農戶無法完全配合水利會依排定之時間進行灌溉作業，另因加入世界貿易組織後面臨之國際農產品競爭壓力，農民希望夠依意願及市場機制種植不同的作物，並依耕作需要進行機動性灌溉，但因渠道系統配置與水利會管理人力上限制，短期內要水利會改變其灌溉管理方式實不容易，因此本研究乃探討農民灌溉行為改變對於灌溉需水量之影響，並對於傳統水利會以供給為導向的灌溉管理制度所造成的衝擊提供較佳解決方案。 研究中以嘉南水利會佳里小組所轄之灌區為研討區域，建立相關資料庫並採用系統模擬的方式模擬出農民自主灌溉下之灌溉水量，其中有關農民決策分析是先列出影響灌溉的評估要素並利用層級分析法建立灌溉意願指標，並由時間與水量上探討灌溉需水量與水利會供給水量之差異，研究中並針對水利會以供給為導向之供水系統與田間農民以需求為導向間之供需不平衡，進行蓄水池之容量設計與風險評估，供作灌溉規劃與管理之依據。 研究中發現農民之灌溉決策受降雨與作物生長期兩個因素影響最大，且農民自主性灌溉將會使得灌溉用水量增加，其中又以旱作用水增加的幅度最高，主要是因為頻繁的灌溉使得土壤水分保持在較高之水準，因而使蒸發散量增加及有效雨量利用量降低。設置蓄水池確能減緩缺水的問題，但仍無法避免缺水，因此本研究提供各種容量設計下之缺水風險曲線，做為設計與管理之依據。

The ChiLi Command area of ChiaNan Irrigation Association was used as the study area. Factors, such as soil, weather, crop kind, crop phenology, time from last irrigation, distance to the diversion source, etc that affecting farmer irrigation behavior were identified and the relation importance of each factor was studied by using Analytic Hierarchy Process. An irrigation will index was proposed by combing the above factors to simulate the irrigation behaviors of farmers. The irrigation demand under farmers’ freewill was estimated by system simulation using historical weather data and was compared with the traditional one. Intermediate storage was also proposed to regulate the mismatch of demand and supply. It is found that the two most important factors affecting farmers’ irrigation decisions are weather and crop phenology. The irrigation demand increased under irrigation management with farmers’ freewill because the effective rainfall decreased as the irrigation frequency increased. Evaportranspiration also increased as the soil moisture was maintained at higher level under frequent irrigation. This is especially true for crops other than paddy. The water shortage decreased with intermediate storage. The design capacity of the storage was also studied with respect to the risk of irrigation shortage.