台灣在農業灌溉用水除了使用渠道灌溉供水外，農民會另以抽取地下水來補足渠道水不足之情形，然農業用水於作物生長階段較多，抽取量也隨之增加，因此本研究於台灣中部彰化莿仔埤圳的三條圳幹線重劃區，利用紀錄表及訪談調查灌區取水情形，針對農民灌溉經驗方式及農田灌溉機制，以系統動力學模式建立一套可自動推估地下抽水及估算灌溉用水量模式，此模式可依循作物生長階段之灌溉基準點及灌溉需水點，自動判斷抽水時間及抽取量，達目標水深後即停止，可減少農民個人操作習慣不同而衍生抽水不一之情形。本研究透過模式得到良好的農業用水模擬結果，探討灌區用水情形，進一步提升農業用水之水源分配效率。 本研究利用2016年二期作水文條件，如降雨、蒸發量、作物生長時程等水文資料，透過灌溉用水模式進行不同水旱作面積比例情形下作物需水量變化模擬，探討灌溉用水情形，後續使農業灌溉用水及地下水方便管理。研究模擬水旱作面積比例0.5比0.5(水稻旱作皆約104.5公頃)的情況下，最大作物需水量於第44天約15500CMD，而在水旱作面積比0.9比0.1(水稻面積約為188公頃，旱作面積約為21公頃)的情況下，最大作物需水量亦發生於第44天約17500CMD，結果顯示作物種植比例及作物生長階段顯著影響灌溉用水情形，當水稻面積增加，灌溉需水量增加，若水稻面積增加渠道供水量並無增加時，田間地下抽水量相對提高。 本研究延伸探討地下水抽水情形與地下水位之影響，結果顯示2015年一期作第一輪區最高平均單位抽水量達6公分，2015年二期作第五輪區最高平均單位抽水量約6公分；由於2015年二期作降雨時空分布較一期作多且均勻，其補給量亦較一期作平均且多，因此灌區2015年一二期作地下抽水情形與地下水位之影響，二期作之抽水情形較一期作在合理抽取範圍。;Taiwan′s agricultural water accounts for about 70% of the total nation’s water consumption in which paddy field irrigation has the largest proportion. Farmers choose to irrigate crops with water extracted from irrigation channel or pumped groundwater. The groundwater pumping issue has recently become a great concern in Taiwan. Taking into account the farmers’ irrigation experience and in-field irrigation operating, this study applies system dynamic model to establish an irrigation water management model for mixed paddy rice and upland crops fields in central Taiwan. This model can automatically identify the groundwater pumping time and the rate. It can reduce the possible human errors of the farmers during the operation of pumping. Moreover, this study, through the model to simulate a good agricultural water results, was able to explored the irrigation water use situation and further to enhance the water distribution efficiency of agricultural water use. In general, the application of channel water and/or groundwater irrigation depends on the crop planting condition, such as crops planting ratio and the growth stage of crops. This research indicates in the case of the 50% paddy rice and 50% upland crops (total area is about 209 hectares), the maximum crop water demand (about 15500CMD) occurs on the 44 days of the second rice crop period in 2016; while in the case of the 90% paddy rice and 10% upland crops, the maximum crop water demand (about 17500CMD) happens on the 44 days of the second rice crop period in 2016. The results shown that the ratio of crops cultivation and the growing stage of crops significantly affect the irrigation water capacity. When the area of paddy rice cultivation increase, the need of irrigation water capacity will increase. However, if the water supply of canal do not increase but the area of paddy rice cultivation increase, the groundwater pumping in the paddy field will raise. By comparing the groundwater level for the first and the second rice crop period in 2015, the second rice crop period has received frequent rainfall with spatial and temporal uniformity is directly proportional to the recharge of groundwater and pumping situation.
