水田灌溉後可再利用迴歸水推估模式之研究

中文摘要提高農業用水效率節約水資源呼聲日高，而水田迴歸水利用乃使農業用水達到更高效率之方法。但影響迴歸水相關因素頗多，其中又以引水量多寡及地形坡度為最重要之影響因子。本研究乃以精密觀測方式探討桃園大圳灌區民國88年水稻二期作及89年水稻一、二期作耕種期間之迴歸水變化情形，並依觀測結果推求迴歸水曲線。在地形坡度為1/150、土壤為砂質粘壤土、滲透係數為4.69mm/day之條件下，假設X為引水量/計畫水量之倍數、Y為迴歸水佔引水量之比例，可得Y＝0.6555X3-6.5653X2 +29.4350X-0.0879；X≧0.0030之關係方程式，若依本研究所得模式推估桃園地區之迴歸水量，在引水量為1倍計畫水量時，迴歸水量約佔引水量之23%。為探討坡度因子對迴歸水之影響性，本研究另以可調坡度之砂箱模型，進行1/100、1/150及1/200等三種不同坡度之迴歸水試驗，結果顯示，土壤質地為砂質粘壤土、滲透係數為0.266mm/day條件下，所得三種不同坡度下之迴歸水方程式型態一致，且與田間觀測之迴歸水曲線型態相似，證明砂箱建置如能使其滲透係數與現場一致，則可用砂箱模擬不同土壤在不同地形坡度之迴歸水推估模式。

關鍵字

砂箱；灌溉；迴歸水；水田

並列摘要

Abstract The usage of return flow in paddy field, which is an effective water conserving method, is more and more important in Taiwan. However, calculating return flow is very complex because of so many influential factors. Irrigation water and topographical slope are the most concernful roles of return flow. This research applies accurate observation methods to study the variation of return flow during the period of second rice crop in 1999 to the second rice crop in 2000 in Tao Yuan irrigation area. By using the observation results, the return flow curve can be developed under the condition of topography slope of 1/150, sandy clay loam, coefficient of permeability of 4.69 mm/day. We obtain the following equation Y＝0.6555X3-6.5653X2+29.4350X-0.0879, X≧0.0030,where X is irrigation water/designed irrigation water, Y is the ratio of return flow to irrigation water. In this research, the return flow in Tao Yuan area is 23% to irrigation water as the irrigation water is one time to the designed irrigation water. To investigate the influence of topographical slope in return flow, the study proceed an experiment in three kinds of slope, 1/100, 1/150, and 1/200, with a slope-adjustable sand box. The consequence equations of return flow under the condition of sandy clay loam, coefficient of permeability of 0.266 mm/day, in three slopes develop the same type which is similar to the model established from Tao Yuan irrigation area. It proves that simulating return flow with sand box in different kinds of soil and slope is feasible and workable as the coefficient of permeability of sand box keeping the same with the field coefficient of permeability.