- 學位論文
植生毯及草種對草溝曼寧係數之影響
RECP and various grass growth effects on the Manning’s Coefficient in open channel flow
摘要
植被型渠道是一種透過其糙度特性和入滲特性來降低徑流速度和流量的最佳管理實踐。透過實驗室試驗，分析了三種不同草類（假儉草、地毯草和百喜草）和滾筒式抗侵蝕產品(RECPs)對渠流曼寧粗糙係數（n）的影響。本研究採用了從當地河岸獲得的砂質粉土，三維錐形侵蝕控制土工格柵和三種類型的草。渠道試驗情形包括每種類型密度為25 g/m2的草，種植時有或沒有帶有RECPs。試驗在三個不同的植被生長階段進行：一個月、兩個月和四個月。總合來說，在1%斜率下使用90 HP泵容量的一種流量條件測試了十八個測試條件。並採用ASTM D6460標準試驗方法進行了豪雨徑流侵蝕性能試驗。 植被覆蓋率隨植被生長而增大。無論有無RECP，百喜草的植被覆蓋率最高。種植四周後，有RECP的植被覆蓋率略高於無RECP的植被覆蓋率。八周後，有RECP的草比沒有RECP的草高，在所有條件下，八喜草最高，其次是地毯草和最後的假儉草。在計算土壤流失率的兩種方法（深度法和重量法）中，三個生長階段的土壤總流失率在無RECP的條件下更大。地毯、假儉草和百喜草的記錄分別為2.20%、2.04%和2.49%。安裝RECP後，地毯、假儉草和百喜草的總土壤流失率分別降低到1.28%、1.17%和1.31%。曼寧係數與植被生長成正比，在使用RECP四周後係數增加。一個月時，地毯、假儉草和無RECP的百喜草的曼寧係數分別為0.015、0.015和0.016，而有RECP的曼寧係數分別為0.016、0.015和0.016。四個月時，無RECP的係數分別為0.019、0.020和0.021，而有RECP的地毯、假儉草和百喜草的係數分別為0.020、0.021和0.024。無論有無RECP，曼寧係數與流量呈負相關。另一方面，曼寧係數、植被覆蓋率和草的高度成正比。 剪應力隨著植被的生長而增大，使用RECP對剪應力有正向影響。無RECP條件下的剪應力值低於使用RECP條件下的剪應力值。 關鍵字：草地植被；滾筒式抗侵蝕產品；生長階段；曼寧係數；明渠流量
並列摘要
Vegetated soil cover is one of the best management practice used to reduce runoff velocity and quantity through its roughness behavior and infiltration. A laboratory study was conducted to analyze the effects of three different types of grass (Centipede, Carpet and Bahia) and Rolled Erosion Control Products (RECPs) on the Manning roughness coefficient (n) in channel flow. Sandy silt soil obtained from a reservoir in Kaohsiung (Taiwan), a three dimensional curled erosion control geomat and the three types of grasses were used in this study. The channel test conditions included each type of grass planted with and without the RECP at a planting density of 25 g/m2. Testing was conducted in three different stages of vegetation growth; one, two and four month(s). In total, there were eighteen test conditions tested using one flow condition of 90 HP pump capacity at 1% slope. ASTM D6460 standard test method was used to conduct the storm-water induced runoff erosion performance test. The vegetation area coverage increase with vegetation growth. Bahia grass had the highest percentage of vegetation area coverage after four weeks with and without RECP. The vegetation coverage for the vegetation with RECP were slightly higher than without RECP four weeks from planting. After eight weeks the grasses with RECP were taller than without RECP, and Bahia grass was the tallest in all conditions followed by Carpet and lastly Centipede grass. The total soil loss rate for the three growth stages were more for the conditions without RECP in both methods of computing soil loss rate (depth and weight methods). Carpet, Centipede, and Bahia grass recorded 2.20 %, 2.04 %, and 2.49 % respectively without RECP. Installing RECP reduced the total soil loss rates by weight to 1.28 %, 1.17 %, and 1.31 % for Carpet, Centipede, and Bahia grass respectively. The Manning’s coefficient was directly proportional to vegetation growth and using RECP increased the coefficients after four weeks. At one month the Manning’s coefficients of Carpet, Centipede, and Bahia grass without RECP were 0.015, 0.015, and 0.016 while with RECP the values were 0.016, 0.015, and 0.016 respectively. At four months the coefficient values were 0.019, 0.020, and 0.021 without RECP while with RECP were 0.020, 0.021, and 0.024 for Carpet, Centipede, and Bahia grass respectively. The relationship between the Manning’s coefficient and the flow rate was found to be negative with and without RECP. On the other hand, the Manning’s coefficient, vegetation coverage and grass height were directly proportional. During testing, the vegetation without RECP bended more than the one without RECP resulting to increased flow velocity. The Manning’s coefficient was negatively affected by the bending of grass. The shear stress increased with the growth of vegetation and the use of RECP had a positive effect on the shear stress. Shear stress values for conditions without RECP were lower than when RECP was used. A positive relationship between shear stress and the Manning’s coefficient was observed. Keywords: Grass vegetation, RECP, Growth stage, Manning’s coefficient, Open Channel flow