本研究為瞭解防風林林冠組成對飛砂防制之效果，選定大安溪與大甲溪鄰近出海口處，飛砂及揚塵危害嚴重地點設立樣區，採集試驗所需之砂粒樣本，再於室內進行砂粒物性分析，並於風洞從事砂粒起動風速、不同林帶厚度、不同吹風時間及林冠組成對飛砂量影響之觀測；試驗結果顯示，大安溪與大甲溪土壤質地皆為級配不良的砂土，密度為2.72g/cm^3與2.66g/cm^3，平均粒徑與形狀係數分別為0.27mm、0.951及0.32mm、0.940，而砂粒含水率皆在1％以下；再者，粒徑2～0.84mm之砂粒其起動風速為13.5～14.5m/s；粒徑0.84～0.42mm之砂粒其起動風速為7.5～8.5m/s；粒徑0.42～0.25mm之砂粒其起動風速為5.5～6.5m/s；粒徑0.25mm以下之砂粒其起動風速低於4.5m/s。又防風林帶最佳攔砂厚度為2.5～3.0倍木麻黃模型高，而不同吹風時間對林後飛砂量變化影響不大，在實驗個案中，吹風10分鐘後飛砂量皆漸趨穩定。至於林冠組成對定砂效果方面，本研究中選用木麻黃及黃槿兩種樹種，組合成10種不同林型配置，結果以前段高後段低之混交林，具有最佳之定砂效果；而低矮之單純林，定砂效果最差。For investigating the sand fixation effects with the tree species combinations of the windbreaks, we chose the estuaries that the locations were with serious harms such as blown sands and dust emissions near Daan and Dajia Rivers to set up the sampling spots for collecting the required sand samples for tests, then performed the sand property analysis indoors and observed the results caused by different wind speeds, sand particle sizes, woodland belt thickness, wind durations, canopy compositions and clown sand quantities in the wind tunnel. The test results indicated that the soil textures of Daan and Dajia Rivers were poorly graded sands with the densities 2.72 and 2.66g/cm^3, average particle sizes and form coefficients 0.27mm, 0.951 and 0.32mm, 0.940, and that the sand moisture contents were all below 1%. Furthermore, the ranges of the start-up wind speeds for different particle sizes 2~0.84, 0.84~0.42, 0.42~0.25mm and below 0.25mm were 13.5~14.5, 7.5~8.5, 5.5~6.5 and 4.5m/s, respectively. The best sand fixation thickness of the windbreak forest belt was 2.5~3.0 times model of beefwood. The different wind durations did not have much influence on the variation of the aeolian sand quality behind the forest and the sand accumulation quantities of the experiment cases after 10-minute wind duration were all stabilized gradually. As far as the sand fixation effects of the forest types, we combined two tree species beefwood and linden hibiscus to 10 different tree arrangements and found that the mixed forest with high woods in the front and low woods behind had the best sand fixation effects. However, the pure forest of the low woods had the worst fixation effects
