| 摘要: | 台灣地區近年來由於社會經濟環境的改變以及人口不斷的增加，造成工商業及公共給水等標的對淡水資源需求大幅增加，加上環境保護及生態保育概念的興起，使得在有限的水資源供給條件下，如何量化水稻田生態及生活之公益機能及充分掌握及運用回歸水以減少灌溉用水量為當前之要務。本研究首先以田區現地試驗與砂箱模型試驗，進行水稻田補注地下水的機制及其入滲率之探討，以量化水稻田之地下水補注功能；其後在考慮灌溉水深、晒田排水及水平滲流量之情形下，進行水稻田灌溉系統之水平衡與最佳化模式之建置。 經於桃園農田水利會桃園大圳二支線灌區中，選擇休耕田區約3分地、硬盤層破壞區3分地、及未休耕區（一般田區）5分地等三處田區進行試驗。結果顯示：在水田湛水之情況下，水稻生長初期之前40天，一般田區之地下水補注率為3.8 mm/day；而硬盤層破壞區之地下水補注率為13.6 mm/day，約為一般田區（具硬盤層）之3.6倍。顯示硬盤層經破壞後，可提高入滲率以增加地下水補注量。唯經由二次的整田及作物生長期間之乾濕交替過程，將逐漸降低土壤入滲率，並於下一期作完全恢復原有硬盤層之機能。 水平衡及最佳化模式對桃園農田水利會11-2輪區以民國89年一期作之氣象資料進行運算結果顯示︰由於第4及第5單區有來自第3單區等上游灌區之回歸水量，第4單區灌溉水量由原計畫（未考慮回歸水再利用）灌溉水量的539.2mm降為247.6mm；第5單區亦由原計畫灌溉水量的539.2mm降為324.4mm。整個輪區經由回歸水再利用，使得灌溉用水量由原灌溉用水量（250,990m3）降低至197,644m3，即減少灌溉用水量達21％，顯示經由本模式可提供上游田區回歸水量及利用上游回歸水之最佳灌溉水量及灌溉時程，以減少灌溉水量，增加水資源使用效益。 Due to changes in the social environment and fast increasing population in Taiwan, the industry and domestic water demand is growing at a fast pace. In addition, the concepts of environment and ecology protection are more and more popular. Consequently the existing water resources become limited. How to quantify the functions from paddy rice field and to utilize efficiently return flow in the farm so as to reduce irrigation demand are the current major tasks. This study is to use field and sandbox model experiments to investigate and quantify the mechanisms of groundwater recharge and infiltration rates in paddy rice field. Furthermore, this study constructs a water balance model with optimization scheme for paddy field irrigation, in which irrigation water depth, drainage when the field is drying, and horizontal infiltration are taken into account. The field investigation was conducted in the irrigation area of Taoyuan main canal for Taoyuan Irrigation Association (TIA), which consists of recession field, hardpan broken field and common field. The results show that at the first 40 days the groundwater recharge rate in common field with flooding is 3.8mm/day, and 13.6mm/day for hardpan broken field. These indicate that after hardpan is broken, the infiltration rate can be raised to increase groundwater recharge. However, after twice field preparation and plant growing periods, the infiltration rate will be reduced and the hardpan function can be fully recovered in the following cultivation. With the climatologic data at TIA 11-2 rotational area at the first cultivation term in 2000, the water balance model with optimization scheme gives the following results. Based on the fact that the fourth and fifth strips collect the return flow from the third strip upstream, the fourth strip needs only 247.6mm of irrigation water, which originally needs 539.2mm without any consideration of return flow. The fifth strip needs 324.4mm instead of 539.2mm. With return flow utilization, the irrigation demand for the whole rotational area drops from 250,990m3 to 197,644m3. It is concluded that this model could be applied to estimate return flow in upstream area and to provide optimum irrigation demand and schedule to conserve water and increase the benefits. |
