結合降雨逕流模式與蓄水選擇函數探究小型集水區水分通過時間之動態變化

Abstract

集水區內水的通過時間(transit time)反映了集水區內水的流動速度和流動路徑的變化，它受到一系列水文作用及集水區特性的控制並對在集水區內的生物地球化學過程有重大影響。通過時間是研究集水區內複雜的水文過程和生物地球化學作用的基礎。蓄水選擇函數(StorAge Selection function,SAS)為近年來推估通過時間及其分佈的重要工具，目前發現在世界很多集水區存在著「逆蓄水效應」，即集水區蓄水量越高時會越偏好釋放蓄水中較年輕的部分，這可能是集水區在蓄水量變動的條件下不同的流動路徑發揮作用所造成的。本研究結合集塊式降雨逕流模式HBV和蓄水選擇函數SAS開發了HBV-SAS模式，模式可以給出集水區流量和同位素的預測，同時計算不同流動路徑的通過時間和不同儲庫蓄水的年齡，為理解集水區內發生的降雨逕流過程有更深入的理解。 研究發現在台灣的福山一號實驗集水區存在「逆蓄水效應」，但這種效應並非見於不同的流動路徑，而是集水區作為一個整體呈現出來的現象。其原因可能是集水區內佔主導的流動路徑會隨降雨強度和集水區蓄水的大小而變動，而儲存在不同儲庫的蓄水彼此之間的年齡相差極大。福山一號集水區的地下水中存在大量不直接貢獻到逕流量的被動蓄水，集水區長期釋放的水都是集水區總體蓄水中較為年輕部分。

The transit time of water reflects the velocity and pathway of water flow through the watershed which is controlled by a series of hydrological processes and characteris-tics of the watershed and plays an important role in biogeochemical processes. Transit time is the basis for research on complicated hydrological processes and biogeochemical processes that take place in the watershed. The StorAge Selection function is an efficient tool for estimating the transit time and its distribution which has been developed in recent years. There is an "inverse storage effect" in most of the watersheds around the world that watersheds prefer to release more young water when their storage is higher. This effect is due to the different flow paths in the watershed under fluctuating storage condi-tions. In this study, the HBV-SAS model has been developed by combining a rainfall-runoff model HBV and the StorAge Selection(SAS) function to estimate the transit time and age of different runoff and reservoirs. this study aims to infer the possible causes of the inverse storage effect. This study found that there is an "inverse storage effect" in the Fushan No.1 exper-iment watershed, a small subtropical watershed in North Taiwan. This effect, which is not shown in every pathway in the watershed, is a phenomenon when the watershed is considered a whole system. The reason is that the dominant pathway varies with rainfall intensity and water storage of the watershed, and the age of different storage reservoirs varies greatly. There is a large amount of passive storage in groundwater that does not directly contribute to runoff. The long-term runoff of the watershed comes from the younger part of the storage.