以水泥圓球模擬石塊覆蓋方式對紋溝間土壤沖蝕之影響機制

Abstract

本研究的主要目的在於探討石塊覆蓋方式對紋溝間土壤沖蝕之影響機制。本研究之沖蝕試驗採用台北縣新店山區的黃壤土，並利用特別設計之試驗箱及人工降雨機進行試驗。試驗箱的坡度固定為20%。利用人造之水泥圓球鋪放在土壤表面作為試驗之覆蓋物，並改變其覆蓋率與覆蓋方式，於兩種強度的人工降雨下進行沖蝕試驗。覆蓋率分別為0%、10%、20%、30%、40%及50%等共六種；而覆蓋方式則採用全部露出土壤表面及部分嵌入土壤中兩種，其埋入率分別為0%與50%；降雨強度則分別為40mm/hr與90mm/hr。 試驗結果發現，有石塊覆蓋之試體，在低降雨強度且覆蓋率低於40%時可降低土壤表面之逕流率；石塊全部露出土壤表面時，對降低逕流沖蝕、飛濺沖蝕，及總沖蝕率之效果較石塊部分嵌入時理想，但在覆蓋率10%時對降低逕流沖蝕及總沖蝕率則是石塊部分嵌入時較好，但兩種覆蓋方式皆能有效降低沖蝕。對降低沖蝕效果而言，當石塊全部露出土壤表面、低降雨強度下且覆蓋率大於40%時效果最好。經迴歸分析結果發現，沖蝕量與覆蓋率、覆蓋物的埋入比率及降雨強度有不錯之關係。

The main purpose of this study is to investigate the effects of rock fragments used as mulch cover on interrill soil erosion. The soil used in the soil erosion tests was collected from a mountainside at Sindian, Taipei County. Erosion Boxes and a rainfall simulator were specially designed and fabricated for this study. During the tests, the slope steepness of the erosion boxes was maintained at 20%. Mortar Balls were placed at the soil surface as the mulch cover. The rate and type of cover were changed, and two different rainfall intensities were simulated and applied in this study. The erosion tests were repeated on soil samples at the cover rates of 0%, 10%, 20%, 30%, 40% and 50% and types of completely exposed to the soil surface and partially embedded into the soil (i.e. the embedded ratio was 0% and 50%), and rainfall intensities of 40 and 90 mm/hr. It was found from the test results that while the rainfall intensity was low and the cover rate was less than 40%, the runoff rate decreased. While the rock fragments were completely exposed to the soil surface, the runoff erosion, splash erosion and total erosion rate were found less compared to that while the rock fragments were partially embedded into the soil. At the cover rate of 10%, it was found that while the rock fragments were partially embedded into the soil, the runoff erosion and total erosion rate were found less. Nevertheless, both the two types of cover could effectively reduced the erosion. It was also found that while the rock fragments were completely exposed to the soil surface, the rainfall intensity was low and the cover rate was greater then 40%, the reducing effect of soil erosion was the best. After regression analysis, an equation was proposed to relate soil erosion, cover rate, embedded ratio and rainfall intensity. The relationship were found very satisfactory.