Paul Truong, D.E. Baker and I.H.Christiansen. Resource Management Institute, QDPI,
Indoorrrpilly, Queensland, Australia.
A large number of field trials were carried out to verify the effectiveness of Monto Vetiver in soil erosion and sediment control in Queensland. The followings are results to date of some case studies:
Steep slope stabilization:
Embankment of both cut and fill slopes can be effectively stabilized by establishing Vetiver on contour lines. The deep root system stabilizes the slope while the hedges reduce runoff, increase infiltration and trap sediment providing a very favorable environment for the colonization by local volunteer species. This is well illustrated in the following two examples.
A very steep (1:1) and highly erodible sodic soil on a railway embankment near Cairns collapsed and needed to be rebuilt after almost every wet season. Obviously, the solution to this problem is a very costly engineering structure. As a trial, six rows of Vetiver were established on mini benches (0.25m wide) on the slope at l m VI (Vertical Interval). A total of approximately 250 m embankment was stabilized with Vetiver in June 1992. The Vetiver established and grew well despite the dry season and by December 1992, the slope was reasonably stabilized by the young Vetiver plants and local species began to establish between the Vetiver rows. In March 1993, nine months later, the slope was completely covered with local vegetation between the Vetiver hedges. Fifteen months later the embankment was completely stabilized with a mixture of Vetiver and mature local grass species. This embankment has withstood up to the last three wet seasons.
On another site, an old quarry at Henlies Hill in Cairns where the old rubble surface has remained bare of vegetation since the quarry operation stopped five years earlier. Four rows of Vetiver, established on an 80% slope at 1 m VI. Despite the extremely poor and hostile conditions of the coarse gravelly ground, Vetiver established well (with NPK fertilizer) and started trapping debris from upslope. The stiff stems of Vetiver provided a very effective barrier trapping debris and rocks up to 70 mm in diameter. Twelve months later the old gravelly slope was 75% covered with local vegetation between the rows of Vetiver hedges which had grown to 1- 2 m tall. Eighteen months later the slope was completely stabilized and revegetated with Vetiver and other local species including a pasture legume (Stylosanthes).
When established across drainage lines and water courses, Vetiver hedges filter and trap both coarse and fine sediment resulting in cleaner runoff water. At Excel Quarry north of Brisbane, Vetiver was used to stabilize steep slopes of overburden and waterways. When planted across a long (500 m) and steep (20%) waterway, Vetiver hedges stopped the erosion on the waterway floor and trapped both coarse and fine sediment in runoff water from this working quarry . On another waterway leading to a dam, Vetiver hedges trapped most fine sediment resulting in less polluted water in the dam. Following the success of these trials, Vetiver is now being used as a standard method of trapping sediment and land stabilization at the quarry.
Vetiver hedges are very effective in stabilizing gully erosion. When planted on contour line above gully head, Vetiver hedges will spread and slow down runoff water and stop the advancement of gully heads. This is well illustrated at a number of gullies in both cropping and grazing lands. Following the control of active erosion at the gully heads, gully floors are normally revegetated naturally with native species.
On large and long gullies where active erosion occurs both on gully floors and walls, Vetiver hedges established on gully floor will reduce flow velocity, trap sediment and reduce further erosion on the floor. At Ashall Creek, a very large gully system in the black earth on the Darling Downs, more than 0.3m of sediment was trapped by a series of 17 hedges over an area more than 400 m long and 50 m wide during the 1994 summer.
Wave erosion control:
Being able to establish and thrive under waterlogged conditions, Vetiver has proved to be very effective in reducing erosion caused by wave action on big farm dam walls. The erosion caused by wave action on the inside wall of a very big farm dam near Cloncurry was effectively controlled by establishing a Vetiver hedge along the high water mark.
Rehabilitation of mining waste and contaminated land:
With its very wide range of tolerance to adverse soil conditions such as pH, soil salinity and mineral including heavy metal toxicities, Vetiver is highly suitable for the rehabilitation of mining waste and contaminated lands. Early results have shown that Vetiver is the most promising species grown on coal mine tailing in Central Queensland (Radloff pers. comm.).
With its wide ranging tolerance of adverse climatic and edaphic conditions the Vetiver hedge system offers a simple and low cost alternative to constructed soil erosion and sediment control measures.
On disturbed lands, where conventional methods of stabilization and reclamation are limited and costly, the Vetiver system offers a unique means of rehabilitation of these highly erodible lands.
More specifically with its high level of tolerance to extreme soil pH, soil salinity, Al and Mn toxicities, Monto Vetiver has great potential for reclamation work in mining and other industrial waste and contaminated lands.