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).
Filter strips:
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.
Gully stabilization:
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.).
CONCLUSION
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.