農業用水約占全台總水量的 70%以上，因此常有用水量過多的存疑，近幾年的研究提到約有四成的灌溉水會回歸地下水，而地下水資源逐漸成為重要的供水來源之一。台南地區擁有較為成熟的灌溉系統，相對而言高雄地區灌溉系統較不完整，農業用水在乾季時，常因水庫及河川水量不足而無法取得，導致部分地區為了補足農業用水而過度抽取地下水。 本研究以系統動力學模式－VENSIM 建立以屏東平原旗山溪及荖濃溪流域為範圍之農業用地與地下水的關聯模式，利用 2018 年至 2022 年之水文資料進行含水層蓄水量分析，探討農業用水對地下水水位之影響，以了解在有限農業用水中可有效利用之水量，模式以相關係數幾乎高於 0.7 為驗證結果，屬於高度相關，以證明模式之適用性。 本研究將農田分為有灌溉與無灌溉之兩種情形作模擬分析，研究範圍內之灌溉面積約 332.64 平方公里（約 46%），結果表明地下水位在有灌溉時會較無灌溉時平均高約 0.01 至 0.5 公尺，表示農田灌溉對地下水位有一定程度的影響；另將無灌溉的模擬結果與降雨資料作比對，可以看出地下水在不考慮灌溉的情況下其蓄水量主要都是根據雨量在做變化。;Agricultural water accounts for more than 70% of the total water volume in Taiwan, leading to concerns about excessive water usage. Recent research indicates that approximately 40% of irrigation water is replenishing groundwater, making groundwater resources increasingly important as a water supply source. The Tainan region possesses a more mature irrigation system, while the Kaohsiung area′s irrigation system is relatively incomplete. During the dry season, agricultural water availability is often insufficient due to inadequate reservoir and river water levels, leading some areas to excessively extract groundwater to meet agricultural needs.
This study utilizes a System Dynamics model - VENSIM to establish a correlation model between agricultural land and groundwater in the Pingtung Plain, specifically focusing on the Qishan Creek and Laonong Creek watersheds. Hydrological data from 2018 to 2022 are used to analyze aquifer storage, investigating the impact of agricultural water usage on groundwater levels. The aim is to understand the optimal water utilization for agriculture under limited water resources. The validation of the model, with correlation coefficients almost exceeding 0.7, demonstrates a high level of relevance, proving the model′s applicability.
The study simulates and analyzes two scenarios for agricultural land: irrigated and non-irrigated. The irrigated area within the research scope covers approximately 332.64 square kilometers (about 46%). The results indicate that groundwater levels tend to be on average 0.01 to 0.5 meters higher in irrigated areas compared to non-irrigated ones, suggesting that agricultural irrigation has a certain impact on groundwater levels. Moreover, the comparison between non-irrigated simulation results and rainfall data shows that groundwater storage primarily fluctuates based on precipitation when irrigation is not taken into account.
