福山森林集水區之輸沙與剝蝕速率研究

Abstract

本研究以福山植物園內之兩個實驗集水區為標的，研究其沈積物搬運特性與其剝蝕速率，以瞭解集水區內地形作用之規模與速率。本研究的研究方法主要是將河川所搬運的物質分為推移質、懸移質與溶解質三大類，進行整體的分析研究。 本研究以堆積區量測法估算集水區推移質總量，以抽樣法建立流量與懸移質和溶解質濃度之率定曲線，再由流量估算懸移質與溶解質總量。由三主物質加總計算集水區沈積物搬運總量，再計算其剝蝕速率。其中哈盆西溪集水區的三年沈積物總量為738公噸，平均年剝蝕量為2.7公釐，而推移質佔7％、溶解質佔90％、懸移質佔3％；哈盆東溪集水區的三年沈積物總量為4372公噸，平均年剝蝕量為5.1公釐，而推移質佔57％、溶解質佔42％、懸移質佔1％。 由航照與衛星影像判識結果顯示在此期間，兩個試驗集水區雖然有茂密的植被，也少有人為干擾，但是依然有大量的沈積物被搬離集水區。由航空照片與衛星影像判識，發現兩個集水區的範圍內並未發生崩塌的情形，因此可判定集水區所搬運的沈積物主要是原本已堆積在河道中或兩側河岸的物質，經過河川的再次搬運作用而移動，並非由新形成崩塌所提供。 研究結果顯示推移質的搬運主要受到颱風與豪雨的控制，這種低頻高能量的事件產生大量的推移質搬運。同時也呈現非線性特性，相同流量的事件並不一定產生類似的推移質搬運量。顯示除了水文條件外，沈積物的分布、體積，以及河道微地形等也是重要因子。

The observation of sediment transportation and denudation of two drainage basins in northeastern Taiwan during 1998 to 2000 shows that significant amounts of sediment have been evacuated from the fluvial system, although the watersheds were well vegetated and not disturbed by human activities. No landslide activity can be observed in aerial photos of this study area during 1998-2000, which implies that the sediment accumulation in the channel systems is the main source of sediment production at the drainage outlets. In this study, bedload was collected in the deposition area at the outlet of each catchment. The quantities of suspended and dissolved sediments were obtained by sampling and the construction of rating curves. The total sediment of the two catchments was 738 tons and 4372 tons, during 1998 and 2000, respectively. The average denudation in this period was 2.8 mm and 5.1 mm, and the bedload, dissolved load and suspended load were about 7%, 90% and 3%, respectively, for Catchment No. 1, and 57%, 42% and 1%, respectively, for Catchment No. 2. The results also show that bedload transportation was controlled by typhoons and heavy rainfalls. These low-frequency and high-energy events can produce large quantities of bedload, but the magnitude of the events and the bedload they transported were not linear. There are also factors that influence bedload transportation other than hydrological conditions, such as the volume and distribution of sediments and the micro relief of the channel.