| 摘要: | 本研究之試驗灌區位於濁水溪沖積扇之上游地區，為一水田混作之灌溉系統，灌溉水源主要為雨水及渠道水，若遇上亢旱時期或渠道水不足時，農民將會抽取地下水來補充灌溉。然而濁水溪沖積扇之地下水區因長期超抽地下水，導致沿海地區地層下陷，且下陷中心正逐漸往內陸之溪州地區轉移。因此本研究透過系統動力模式來建立水田混作之精密灌溉系統，探討2018年一期作隨時變之田間用水因子、不同水旱作面積比例下之灌溉用水量、不同年度一期作之地下水抽取量，以及2018年一期作入流量減供情境下之節省水量。
結果顯示2018年一期作真實水旱作面積比例(約0.5：0.5)之灌溉用水量為1.539公尺，該值在臺灣中部第一期作輪灌下水稻灌溉用水量之基準值1.750公尺範圍內，水田灌溉用水量為81.02%，旱田灌溉用水量為18.98%；水旱作面積比0.7：0.3之一期作灌溉用水量為1.768公尺，相近於水稻灌溉用水量之基準值，水田灌溉用水量為87.91%，旱田灌溉用水量為12.09%；水旱作面積比0.9：0.1之一期作灌溉用水量為2.110公尺，高於水稻灌溉用水量之基準值，水田灌溉用水量為96.41%，旱田灌溉用水量為3.59%。
在入流量減供之情境下，2018年一期作入流量減供20%下試驗灌區之平均單位面積抽水深0.294公尺，低於2016年一期作試驗灌區之平均單位面積抽水深0.300公尺，故該情境在合理抽取地下水範圍內，並可節省1.213百萬噸的灌溉水；2018年一期作入流量減供30%之平均單位面積抽水深0.332公尺，雖低於2015年一期作之平均單位面積抽水深0.382公尺，但已高於2016年一期作之平均單位面積抽水深，建議亢旱時期在使用此情境；2018年一期作入流量減供50%之平均單位面積抽水深0.414公尺，已明顯高於2015年與2016年一期作之平均單位面積抽水深，故本研究不建議使用減供50%之情境，以免過度抽取地下水。;The study area is located upstream of the Choushui river alluvial fan. It is an irrigation system that mixes paddy rice and upland crops. The irrigation water in the study area is mainly from rainfall and channel water. In the event of drought or when the channel water is insufficient, farmers will pump groundwater for irrigation. However, the littoral area of the Choushui river alluvial fan has subsided, which is caused by long-term groundwater over pumping, and the central of subsidence area is gradually moving to inland area. Therefore, the purpose of this study is to use system dynamic model to develop a precise irrigation system for mixed paddy rice and upland crops, and to analyze the time-varying water balance of the first crop rice in 2018. Finally, this study evaluates the amount of diversion requirement under different rice and upland crop area ratios, the amount of groundwater under the first crop rice of different years, and the water savings under the channel water supply reduction in 2018.
The simulation results show that in the case of 50% paddy rice and 50% upland crops, the diversion requirement in the first crop rice was 1.539 meters in 2018. This value is within 1.750 meters, which is the reference value for diversion requirement in the first crop rice of central Taiwan. The amount of diversion requirement for paddy rice is 81.02%, and that of upland crops is 18.98%. In the case of 70% paddy rice and 30% upland crops, the diversion requirement in the first crop rice was 1.768 meters in 2018. This value is similar to the reference value for diversion requirement in the first crop rice of central Taiwan. The amount of diversion requirement for paddy rice is 87.91%, and that of upland crops is 12.09%. In the case of 90% paddy rice and 10% upland crops, the diversion requirement in the first crop rice was 2.110 meters in 2018. This value is higher than the reference value for diversion requirement in the first crop rice of central Taiwan. The amount of diversion requirement for paddy rice is 96.41%, and that of upland crops is 3.59%.
In the case of a 20% reduction in channel water, the average pumping depth per unit area in the first crop rice of 2018 was 0.294 meters. This value is less than 0.300 meters in 2016, so the case is reasonable to pump groundwater and save 1.213 million tons of irrigation water. In the case of a 30% reduction in channel water, the average pumping depth per unit area in the first crop rice of 2018 was 0.332 meters. This value is less than 0.382 meters in 2015, but it is more than 0.300 meters in 2016. Therefore, this study suggests that this case should be used during the drought. In the case of a 50% reduction in channel water, the average pumping depth per unit area in the first crop rice of 2018 was 0.414 meters. This value has been significantly more than the average pumping depth per unit area in 2015 and 2016. In order to avoid over pumping of the groundwater, this case is not recommended for this study. |
