水資源是二十一世紀人類所面臨最重要的議題之一，由於受到全球氣候變遷的影響，河川流量的枯豐期有極端化的趨勢，使得水資源供需調配趨於困難，因此發展出各種模擬集水區流量的水文模式作為水資源管理與規劃的參考。GWLF(General Watershed Loading Function)為模擬集水區水量水質分析模式，操作上面也相當容易，目前已廣泛被應用在相關研究中。 由於GWLF 模式在蒸發散量和土壤的滲漏量呈現高估的情況，且低估連續不雨的地下水出流量，因此本研究修改模式架構，在蒸發散計算方面加入土壤水分因子增加土壤阻抗，在滲漏量計算中考慮未飽和含水量與水力傳導度，並在表土根層考慮大孔隙流量，使修改後的模式能應用於日流量的模擬。本研究針對蘭陽溪流域，運用土地利用型態資料與收集的水文氣象資料，輸入修正後GWLF 模式中進行集水區流量之模擬。 結果顯示，修正後的模式改善表土根層於水分缺乏時蒸發散量推估過多的情況，而模擬的月流量、旬流量及事件模擬的日流量情況修正了原始模式流量低估的問題，因此改良後的模式能更精確掌握不同時距流量的變化情況。Water resource is an important issue in the 21th century. Due to the climate change, the streamflow is becoming varied extremely in wet seasons and dry seasons. The supply and demand of water resource is much more difficult to meet everyone’s expectations. Therefore, numerous models simulate the streamflow are established which yield good examples of water resource management. General Watershed Loading Function (GWLF) is one of the models that analyzes the quantity and quality of water in catchment areas which is easy to operate so that it’s widely used in related researches. For the original GWLF overestimates evapotranspiration and vertical percolation, and underestimates groundwater flow at periods lacking rains, this research had made some modifications to GWLF model and applied it to simulate the water flow of catchment area of Lan-Yang River by entering the current status of land utilization, hydrological data and meteorological data to the model. This modified model takes soil resistance into consideration when calculating evapotranspiration, and meanwhile adds the parameters of moisture content in unsaturated zone and hydraulic conductivity to the calculation of vertical percolation. This model also considered preferential percolation of rootzone. The modifications enable the GWLF model to simulate the nature of daily streamflow. The result indicated that the modified GWLF model could improve the calculation of percolation and evapotranspiration in root zone in dry seasons. As the penetrated percolation enhances groundwater flow, we adjusted the underestimations at periods lacking rains to simulating daily streamflow. It shows that the modified GWLF model can be more appropriate for simulating not only monthly but daily streamflow.
