3-D TRF and various grass growth effects on the Manning’s coefficient in open channel flow

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 Centipede, Carpet and Bahia grass and Rolled Erosion Control Products (RECPs) on the Manning’s coefficient in channel flow. Sandy silt soil obtained from a reservoir in Kaohsiung (Taiwan), a three-dimensional RECP and the different grasses were used. The test conditions included each type of grass planted with and without the RECP at a planting density of 25 g/m2. The grasses were tested at one, two and four month(s) after planting in reference of ASTM D6460 standard.
Installing RECP increased the vegetation area coverage one month from planting. The use of RECP had less or no effect on Carpet and Centipede grass height, only Bahia grass height was increased after one month. 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. The shear stress increased with the growth of vegetation and the use of RECP increased shear stress.