Influence of coconut fiber meshes on the scouring characteristics of engineering accumulation slopes

Coconut fiber mesh can be used to reduce the runoff and sediment yield on the surface of the slope after engineering accumulation. The study aims to explore the effectiveness of coconut fiber mesh under hydraulic erosion and runoff scouring. A series of experiments were also carried out to simulate the runoff scour on the engineering accumulation under different flow discharges (1.4, 2.0, 2.6, and 3.2 L/min) and coconut fiber mesh cover with two mesh sizes (5 and 10 cm). A systematic investigation was then performed on the runoff and sediment yield patterns, hydrodynamic characteristics, and rill erosion morphology after surface runoff scour. The results indicated: 1) A mesh with the 10 cm aperture size extended the initial runoff time on the engineering accumulation slope by 11 to 27 s, while the 5 cm mesh size increased the time by 35 to 41 s. The 10 cm mesh significantly reduced the surface runoff on the engineering accumulation slope by 10.21% to 15.65%, while the 5 cm mesh reduced the runoff by 12.12% to 20.73%. Similarly, the 10 cm mesh reduced the sediment yield on the engineering accumulation slope by 25.20% to 33.64%, and the 5 cm mesh was reduced substantially by 42.58% to 73.06%. 2) The resistance coefficient increased significantly to reduce the water flow velocity, shear stress, and runoff power, particularly after the application of the mesh on the slope of engineering accumulation. There was a decrease in the size and connectivity of erosion rills and drop structures on the slope, indicating the high benefits of runoff and sediment reduction. The 5 cm mesh with its denser grid performed better to intercept the water and sediment, compared with the 10 cm mesh. 3) There was a significant linear relationship between the average rill width and both surface runoff and sediment yield (P<0.05) under the coverage of coconut fiber mesh. In terms of runoff, the fitting slope for the 5 cm mesh (24.25) was greater than that of the 10 cm mesh (19.15) and the bare slope (14.43). As such, the 5 cm mesh was better reduced the runoff. In sediment yield, the fitting slope for the 5 cm mesh (0.70) was between the values for the 10 cm mesh (0.66) and the bare slope (0.74). The intersection of the fitting lines for the 5 and 10 cm meshes occurred at x=33.75. The 5 cm mesh shared the superior performance to reduce the sediment at the stage of ephemeral rill erosion, compared with the 10 cm mesh. Coconut fiber mesh with its porous structure and grid layout significantly reduced the runoff and sediment yield on the slope. The internal voids of the coconut rope retained the sediment in the runoff to reduce the runoff shear force and power. The slope was then stabilized to inhibit the expansion of erosion rills. The grid layout was evenly distributed on the sediment deposition to form the low soil banks. The flow velocity was then slowed down to promote the water infiltration. Finally, the soil erosion was effectively reduced on the slope. The findings can provide scientific data to support the soil and water conservation measures for the slopes of engineering accumulation in construction projects. Additionally, new insights can be offered to optimize the temporary protective measures for engineering accumulations.