木瓜溪流域水土資源利用與地方發展──以吉安大圳為例

Water Resource Utilization and Local Development in the Mugua River Basin—A Case Study of the Ji’an Canal

「吉安大圳」從日治時期起，長期以來一直使用木瓜溪作為農業灌溉水源，至今仍是吉安鄉主要的農業水源。然而，近年來的缺水乾旱，使得木瓜溪發電尾水減少，農業不得不採取水資源調配和停灌措施。此現象凸顯了氣候變化對農業經濟的直接衝擊，同時也提醒地方需積極管理水資源。
木瓜溪具備優越的自然條件，成為東部地區重要的水力發電來源，也是台灣水力電廠最集中的溪流之一，水力發電不僅提供東部地區超過80年的穩定電力供應，同時對自然環境的破壞相對較低，符合水資源永續利用的理念。而流域下游沖積扇主要依賴吉安大圳進行農業灌溉，吉安鄉在2017年的種植面積最廣，農業產值達8億元；而在水資源發電產值方面，則約45億元，初步估算，木瓜溪流域的水資源產值每年約達50億元。
此外，避免農業生產中過量肥料使用導致土壤和環境污染，建議在經濟效益和生態環境之間取得平衡，選擇施肥較少但仍能維持收成量的四季豆、食用番茄、胡瓜和食用玉米等作物，實現更環保和永續的農業生產方式。在水質檢測方面，人口數、灌溉面積和牲畜數等變數與土壤中的氮素和磷素呈顯著相關，這些結果強調了對水資源確實地掌握和控管的重要性，以避免對自然環境造成負面影響，並實現「綠色經濟」和「永續農業」的目標。

The ''Ji'an Canal'' has been using the Mugua River as its primary agricultural irrigation source since the Japanese colonial period and remains the main agricultural water source for Ji'an Township. However, in recent years, water scarcity and drought have led to reduced flows in the Mugua River, forcing the adoption of water resource allocation and irrigation suspension measures in agriculture. This phenomenon underscores the direct impact of climate change on the agricultural economy and serves as a reminder to local authorities of the need for proactive water resource management. The Mugua River possesses excellent natural conditions, making it a significant hydropower source in the eastern region and one of Taiwan's most concentrated rivers for hydropower generation. Hydropower does not only provide a stable electricity supply to the eastern region for over 80 years but also causes relatively lower environmental damage, aligning with the principles of sustainable water resource utilization. In the downstream alluvial fan, agriculture heavily relies on the Ji'an Ditch for irrigation. In 2017, Ji'an Township had the widest cultivation area, with agricultural output reaching 800 million NTD, while the water resource power generation value amounted to approximately 4.5 billion NTD. Preliminary estimates indicate that the annual water resource value in the Mugua River basin reached to about 5 billion NTD.
Additionally, in order to avoid excessive use of fertilizers, causing soil and environmental pollution, it is suggested to strike a balance between economic benefits and the ecological environment. Opting for crops like string beans, edible tomatoes, cucumbers, and sweet corn that require less fertilization while maintaining crop yields would promote more environmentally friendly and sustainable agricultural practices.
Regarding water quality testing, variables such as population, irrigation area, and livestock are significantly correlated with nitrogen and phosphorus content in the soil. These results emphasize the importance of accurately managing water resources to prevent negative impacts on the natural environment and to achieve the goals of a ''green economy,'' and ''sustainable agriculture.''