石塊覆蓋對紋溝間土壤沖蝕及薄膜流流速之影響

Abstract

本研究主要目的在於探討石塊覆蓋方式對於薄膜流之流速及紋溝間土壤沖蝕之物理現象及機制。本研究之沖蝕試驗採新店黃壤土利用人工降雨機在低降雨強度(39 mm/hr)變換四種覆蓋率(0%、15%、30%及50%)；兩種放置方式(石塊完全露出及石塊部份嵌入)進行長時間之觀測。其結果顯示，石塊完全露出能隨覆蓋率增加而入滲量增加；石塊部份嵌入趨勢則隨覆蓋率增加而入滲量減少。在土壤沖蝕方面，石塊完全露出及石塊部份嵌入皆能降低土壤沖蝕量，但石塊完全露出隨石塊覆蓋率增加有較佳能力減少土壤沖蝕量；石塊部份嵌入在覆蓋率不一樣造成土壤表面薄膜流流動型態不同造成沖蝕量非線性變化。在經流速量測、試驗影像觀察及文獻回顧後，發現低降雨強度下，薄膜流無法對土壤表面產生剝離作用(detachment)，僅能對雨滴撞擊產生剝離之土壤顆粒進行傳輸，故飛濺沖蝕則會是土壤沖蝕及傳輸之重要營力。

The main purpose of this study is to investigate the effects of rock fragments used as mulch cover on interrill soil erosion and the velocity of sheet flow. The soil used in the soil erosion tests was collected from a mountainside at Sindian, Taipei County. Soil erosion tests were repeated, cover rates of 0%,15%,30% and 50%, types of completely exposed to the surface and partially embedded into the soil, using a rainfall simulator with a rainfall intensity of 39 mm/hr. The results showed that while the rock fragments were completely exposed to the soil surface, the infiltration effectively increased, however the rock fragments were partially embedded into the soil, the infiltration was different. Both types of completely exposed to the surface and partially embedded into the soil were found to be able to decrease soil erosion. The rock fragments which were completely exposed to the surface could reduce soil erosion more effectively. For the rock fragments which were partially embedded into the soil, soil erosion and cover rate seemed to exist a non-linear relationship. The reason for that may because that the sheet flow on the soil surface was different. After measuring sheet flow velocity, watching test’s DV (Digital Video) and reviewing paper, it could be found that sheet flow at the rainfall intensity of 39 mm/hr could not detach soil particles. In this study, sheet flow could only transport soil particles detached by raindrop impact. In other words, Splash erosion dominated the interrill erosion.