|摘要: ||台灣西部沿海地區飛砂問題嚴重，雖防風林帶已廣泛種植以防杜風害與砂害，然防風林帶樹種組合之不同，對於定砂效果必然相異，且近年來國內廣泛推廣混交林以強化更新林相之防護機能。本研究針對低木、高木與混交林等三種林況，分別設計十組不同林型，每種林型厚度皆為4H，分別為純高木組成之A-8型、純低木組成之B-8型與林型1～8之混交林型等共十組，利用風洞設備進行吹砂試驗，探討定砂功效之異同，低木樹種選擇黃槿(Hibiscus tiliaceus L.)，高木樹種則選擇木麻黃(Casuarina equisetifolia L.)作為代表，實驗用砂取自大安溪與大甲溪出海口處飛砂嚴重區域，並配合砂粒物性分析以了解砂粒之特性。|
The coastal areas at the western Taiwan have serious problems of aeolian sand. Although the windbreak forest belt has been extensively planted to prevent wind damage and sand damage, however, the different sand fixation effect between difference combination of tree species of windbreak forest belt will be dissimilar inevitable. Moreover, in recent years, mixed layered forest has been widely promoted in Taiwan to enhance the protection function of renewal forest. The research aimed at three kinds of forests conditions of low woods, high woods, and mixed forest to design ten different forest types. The thickness of each forest type was 4H, and they were: Type A-8 consisted of pure high wood, Type B-8 consisted of pure low wood, and eight mixed forest types of Type 1~8. The sand blowing test in wind tunnel was utilized to explore the difference of sand fixation effect. The tree species of low wood adopted Linden hibiscus (Hibiscus tiliaceus L.), and Beef Wood (Casuarina equisetifolia L.) was chosen as the representative of the tree species of high woods. The experiment sands were got from the districts of serious aeolian sand at the mouths of Da-an River and Dajia River, and the research cooperated with the physical property analysis to understand the features of sands.
The results of physical property analysis: The on-site moisture content of Da-an River and Dajia River was both under 1.2%; the average grain diameter was 0.14mm and 0.22mm; the average density was 2.72g/cm3 and 2.66 g/cm3; the texture was both sandy soil, but the sands of Dajia River was closer to ball shape.
The results of wind tunnel test: The start-up wind speed was between 5.0 and 8.0m/s when the range of sand grain diameter was 0.25～0.84mm; the start-up wind speed was 4.0m/s when the sands diameter was smaller than 0.25mm; the best sand fixation thickness was 2.5H~3H; different duration did not have much influence on the variation of aeolian sand quantity behind the forest; the air flow field measuring results: the boundary layer thickness was 25cm approximately.
Type B-8 of pure forest of Linden hibiscus had the most sand accumulation quantity behind the forest belt; the sand hill accumulated behind the forest primarily, and its sand fixation effect was the worst. Therefore, the sand fixation effects of forest types with high woods were better than the forest type with pure low wood. Forest Type 4’s sand fixation effect achieved 90%; however, the sand hill within the forest belt had the phenomenon of stretching to the place behind the forest belt. If considering the forest type of slow sand accumulation, better protective property to the place behind the forest belt, and second sand fixation effect, Type 1 (low wood and high wood staggered by single row) was the best sand fixation forest type.