| 摘要: | 由於全球氣候變遷影響，對於具備灌溉設施的農業生產系統而言，頻繁且明顯的用水不均現象正在持續地發生，而對於屬於看天田之區域，用水短缺現象則更為嚴重。臺灣年降雨達2,500公釐，但80%的雨量發生在夏季，而且大多的降雨是由颱風所造成，由於降雨在時間與空間上的分佈不均，更加遽了乾旱及洪水的發生頻率。臺灣除了面臨極端氣候造成的問題，在佔用水量最大宗的農業用水方面，若能於有限的水資源條件下，增加用水的精確性，則可提升水情不佳時期的用水調整彈性。由於現有的灌溉系統多以人工操作為主，以致操作及輸送水源時，造成相關的輸水損失仍有必要的精進空間，因此提升田間灌溉用水管理績效及以現代化灌溉系統增加用水調控之精確，乃為乾旱時期提供足夠水量予作物生長及確保產量的良方。
於此，本研究以位於中部臺灣的彰化地區，屬莿仔埤圳灌溉系統的三條圳幹線灌區，以現地環境及水文條件，引用水平衡理論，經由系統動力模型建立研究區域水、旱田用水估算模式，除了降雨的補充，地表水與地下水於此管理模式中，均被視為灌區用水來源。本研究建立之智慧灌溉管理系統，經由田間監測設備回傳現地水深及相關水文參數，可自動計算水田及旱田之需水量，並自動判別渠道水源是否充足，而選擇以明渠或地下水水源進行灌溉，透過精密灌溉系統有效提升田間灌溉管理之精確，使研究區域水、旱田混作區域達到精密灌溉及提升灌溉管理績效。
本研究以102年水文氣象資料模擬缺水時期減供灌溉計畫水量30%及50%等兩種情境，探討其對於灌區作物之影響，結果顯示，於減供灌溉計畫30%水量之條件下，田間作物用水僅少量受到影響，故在抗旱初期，應可將其納為第一階段之應變策略。然於用水條件更為拮据之階段，施行灌溉計畫50%水量減供策略，依模擬結果顯示，應注意用水調節、管控及採輪灌措施，並更頻繁地調整水門，以避免下游灌區因無法獲得水源而達土壤凋萎點，造成下游灌區作物損失。
此外，本研究採104年二期作之水文條件進行模擬，顯示若上游灌區水源得以經模式控制，調整部份水源由地下水提供，則可相對減少其對於渠道水源之取用量；換言之，以此模式可達成調配渠道水量予下游灌區使用，並以地下水源為上游灌區進行補充灌溉，可使各個輪區渡過枯旱缺水時期。而經本研究延伸探討以位於研究區域上、下游地下水位監測井同時期水位歷史數據，分析比對當地地下水位變化，結果顯示該抽水容積，對於當地地下水位之影響，尚在合理範圍內。故若能於灌溉系統上游灌區，經評估及監測地下水位變化後，適當且適量地使用地下水作為補充灌溉水源，可使地下水更合理且有效被運用於解決乾旱時期之用水調配問題，同時，配合本研究所建立之智慧灌溉管理系統，將可有效應用田間監測所得大量數據，經由物聯網進行雲端運算後，即時為農田灌溉用水量及水源選定作出自動計算及提供決策參考，其成果有助於提升田間灌溉管理績效並達成精進灌溉節水之目標。
;The agroecosystems of irrigated area are experiencing frequent and pronounced water imbalances such as water deficit which is more serious in rain-feed area as a consequence of global climate change.
Taiwan average annual rainfall is approximately 2,500 mm. In particular, 80% of the rainfall occurs in summer, and most of the heavy rainfall is caused by typhoons. The situation is worsening as climate change results in uneven rainfall, both in spatial and temporal terms. Moreover, climate change has resulted the variations in the seasonal rainfall pattern of Taiwan, thereby aggravating the problem of drought and flooding. However, due to increasing demands and continuous competition for high quality water resources in the agricultural-industrial-domestic triangle, it is unrealistic to expect further expansion of agricultural irrigation. But it’s possible to enhance the flexibility of water regulation by increasing the accuracy of water use under limited water resources. Since the irrigation water distribution system is mostly manually operated, which produces difficulty with regard to the accurate calculation of conveyance losses of channels and fields. Therefore, making agricultural water usage more efficient in the fields and increasing operational accuracy by using modern irrigation systems can ensure appropriate irrigation and sufficient yield during droughts. If agricultural water, which accounts for 70% of the nation’s total water usage, can be allocated more precisely and efficiently, it can improve the efficacy of water resource allocation.
In this study, a system dynamic model was used to establish an irrigation water management model for a companion and intercropping field in Central Taiwan. In addition to rainfall replenishment, both surface water and groundwater were considered as water sources for irrigation use. The intelligent irrigation management system established in this study can automatically calculate the water requirement of intercroping fields through the field monitoring equipment to obtain the current water depth and related hydrological parameters and automatically determine whether the channel water sources are sufficient and choose to use open channels or groundwater sources for irrigation. The precise irrigation system effectively improved the accuracy and the performance of field irrigation management in the mixed cropping area in the study region.
The model simulated two scenarios by reducing 30% and 50% of the planned irrigation water in year 2013. Results indicated that the field storage in the end block of the study area was lower than the wilting point under the 50% reduced irrigation water scenario. The original irrigation plan can be reduced to be more efficient in water usage, and a 50% reduction of irrigation can be applied as a solution of water shortage when drought occurs. However, every block should be irrigated in rotation, by adjusting all water gates more frequently to ensure that the downstream blocks can receive the allocated water to get through the drought event.
In addition, this study simulated the hydrological conditions of the 2nd crop season in year 2015. It shows that if the water supply in the upstream irrigation area is controlled by the model and some of the water supplied by the groundwater, the amount of water used from channel can be relatively reduced. In other words, to reach the water allocation for downstream irrigation use, groundwater sources for the upstream area can be appropriately used for irrigation, which enabling each rotation block to pass through the water shortage period. The historical data of groundwater level monitoring wells in the upstream and downstream location of the study area are extended to be discussed in this study. The changes of local groundwater level are analyzed and compared. The results show that the volume of the pumping water is still within a reasonable range for the local groundwater level. Therefore, if the groundwater is properly used as a supplementary irrigation source after assessment and monitoring of the groundwater level changes in the upstream irrigated area, groundwater can be used more reasonably and effectively to solve the problem of water allocation during the drought period. At the same time, the smart irrigation management system established in this research can be operated effectively to use the big data collected from field monitoring. After cloud computing via the Internet of Things (IoT), it will automatically calculate and provide decision-making references for the selection of farmland irrigation water and water sources. The results will help to improve field irrigation management performance and achieve the goal of improving irrigation and water conservation. |
