曾文溪及高屏溪流域動態儲水量之評估與比較

Abstract

本研究以臺灣南部四個流量測站（曾文水庫、里嶺大橋、大津橋、六龜）所圍的集水區為研究對象，透過質量平衡與退水速率-流量函數方法，分別估算2003-2020年間總動態儲存（ST）、直接儲存（Sd）與間接儲存（Si）之長期趨勢及年際變化。結果顯示，各測站總動態儲存變化具有明顯的年際差異，曾文水庫於莫拉克颱風（2009年）前後儲水行為呈現顯著轉變，降雨期間波動幅度由大至小，反應儲存空間的減少。四個集水區直接儲存與間接儲存佔總動態儲存比例排序顯示，曾文水庫直接儲存占比最高，或許受到壩體攔截對流量觀測包含地表下逕流之影響；里嶺大橋則以間接儲存占比最高，顯示其沖積扇地形及厚層沉積物對地下水儲存的潛在影響。進一步計算總動態儲存變化占年雨量比例，結果顯示不同集水區間存在明顯差異，反應各流域儲水的空間異質性。此比例可作為衡量流域將降雨轉化為可變動儲存之指標，適用於跨流域與年際間的比較分析。本研究亦針對間接儲存於流域管理的應用提出討論，認為其可作為傳統地下水位監測之外之補充指標，特別適用於監測井稀少地區，並有助於辨識具補注潛力之關鍵區域。本研究成果可為區域地下水管理與補注規劃提供參考，並建立後續相關研究之基礎。This study examines the catchments delineated by four streamflow gauging stations in southern Taiwan—Zengwen Reservoir, Liling Bridge, Dajin Bridge, and Liugui—using water balance and recession rate–discharge function methods to estimate the long-term trends and interannual variations of total dynamic storage (ST), direct storage (Sd), and indirect storage (Si) for the period 2003–2020.The results show marked interannual differences in total dynamic storage among the stations. At Zengwen Reservoir, a distinct shift in storage behavior occurred before and after Typhoon Morakot (2009), with the amplitude of fluctuations during rainfall periods decreasing, reflecting a reduction in available storage capacity. Ranking the proportions of direct and indirect storage relative to total dynamic storage across the four catchments revealed that Zengwen Reservoir had the highest proportion of direct storage, potentially influenced by the dam’s interception effect on streamflow observations, including subsurface runoff. In contrast, Liling Bridge exhibited the highest proportion of indirect storage, indicating the potential influence of its alluvial fan geomorphology and thick sedimentary deposits on groundwater storage.Further analysis of the ratio of total dynamic storagechange to annual rainfall showed clear differences among catchments, reflecting spatial heterogeneity in storage responses. This ratio can serve as an indicator for assessing the efficiency of converting rainfall into variable storage, facilitating inter-catchment and interannual comparisons. The relevance of indirect storage in watershed management was also discussed, noting its potential use as a supplementary indicator to conventional groundwater-level monitoring, particularly in areas with sparse observation wells, and its value in identifying zones with recharge potential.The findings provide reference information for regional groundwater management and recharge planning, and establish a basis for future related research.