Effectiveness of Vetiver Grass in Char Land Protection

Numerous land protection techniques are available but all of them are not always suitable due to various factors such as resource limitations, cost-effectiveness and environmental impacts. This research work aims to focus on the protection of char land (small river islands) which are highly erodible and unstable due to high tidal flow and flood actions. Bioengineering technique is effective in increasing bed roughness. In this context, vetiver grass (Chrysopogon zizanioides) has been selected for its special characteristics such as fast growth, submergence tolerance and long root system. Even though there has been studies on the roughness coefficient (n) of vegetated soil, there is still gap in study on char land. For this purpose, a small-scale physical model-based experiment and theoretical studies were conducted. A rectangular wooden model with a dimension of 3.0 m × 0.7 m × 0.6 m filled with char soil and a mild bed slope of 1:60 was constructed. Vetiver tillers were planted with a spacing of 20 cm c/c in both directions. Model tests were conducted after 140 days of vetiver plantation varying the discharge in the range of 0.000111–0.000138 m3/s to determine n. The vetiver root system grew to a depth of 50 cm and anchored the bed soil. Vetiver shoots grew up to 127 cm and retarded the flow velocity and also increased the surface roughness and flow depth. Theoretical relationships have been established using Manning’s roughness equation, and Strickler’s formula for determining the Manning’s Roughness Coefficient, n of the char land for a discharge range of 0.002–0.004 m3/s. Manning’s roughness coefficient was found to be in the range of 0.03–0.07 for different roughness heights. It is concluded that vetiver grass plantation is effective in char land protection and reclamation by increasing roughness, retaining soil and reducing erosion.