SLOPE STABILISATION USING VETIVER SYSTEM

Besides soil erosion, the Vetiver System (VS) can reduce or even eliminate many types of natural disasters, including landslides, mud slides, road batter instability, and erosion (river banks, canals, coastlines, dikes, and earth-dam batters). Vetiver is very effective when planted closely in rows on the contour of slopes. Contour lines of vetiver can stabilize natural slopes, cut slopes and filled embankments. Its deep, rigorous root system helps stabilize the slopes structurally while its shoots disperse surface run-off, reduce erosion, and trap sediments to facilitate the growth of native species.

Characteristic of Vertiver Plant:

a. vetiver plants used in land stabilisation applications behave more like fast-growing trees or shrubs. Vetiver roots are, per unit area, stronger and deeper than tree roots.

b. Vetiver’s extremely deep and massive finely structured root system can extend down to two to three meters (six to nine feet) in the first year. On fill slope, many experiments show that this grass can reach 3.6m (12 feet) in 12 months. (Note that vetiver certainly does not penetrate deeply into the groundwater table. Therefore at sites with a high groundwater level, its root system may not extend as long as in drier soil). Vetiver’s extensive, and thick root system binds the soil which makes it very difficult to dislodge, and extremely tolerant to drought.

c. As strong or stronger than those of many hardwood species, vetiver roots have very high tensile strength that has been proven positive for root reinforcement in steep slopes.

d. These roots have a mean tested tensile strength of about 75 Mega Pascal (MPa), which is equivalent to 1/6 of mild steel reinforcement and a shear strength increment of 39% at a depth of 0.5m (1.5 feet).

e. Vetiver roots can penetrate a compacted soil profile such as hardpan and blocky clay pan common in tropical soils, providing a good anchor for fill and topsoil.

f. When planted closely together, vetiver plants form dense hedges that reduce flow velocity, spread and divert runoff water, and create a very effective filter that controls erosion. The hedges slow down the flow and spreads it out, allowing more time for water to soak into the ground.

g. Acting as a very effective filter, vetiver hedges help reduce the turbidity of surface run-off. Since new roots develop from nodes when buried by trapped sediment, vetiver continues to rise with the new ground level. Terraces form at the face of the hedges, this sediment should never be removed. The fertile sediment typically contains seeds of local plants, which facilitates their re-establishment.

h. Vetiver tolerates extreme climatic and environmental variation, including prolonged drought, flooding and submergence, and temperature extremes ranging from -14ºC to 55ºC (7º F to 131ºF) (Truong et al, 1996).

i. This grass re-grows very quickly following drought, frost, salt and other adverse soil conditions when the adverse effects are removed.

j. Vetiver displays a high level of tolerance to soil acidity, salinity, sodicity and acid sulfate conditions (Le van Du and Truong, 2003).