BIO-ENGINEERING
MEASURES BY VETIVER SYSTEM
Background
Growing of Vetiver hedges on
contours and adopting conservation tillage practices between them has been proved
to be an effective method to reduce runoff and soil loss, and increase in-situ
moisture, thereby obtaining higher crop yields. The species of Vetiver System (Chrysopogon
zizanioides), originates in the state of Tamil Nadu, South India, which is now
being promoted in nearly 120 countries. It is sterile, non invasive and has to
be propagated by clump subdivision. Generally nursery multiplication of bare
rooted plants is the preferred method. The average multiplication rate varies
but is normally, in a nursery, about 1:30 after about three months. The Vetiver
System (VS) can reduce or even eliminate landslides, mudslides, road batter instability,
and erosion (river banks, canals, coastlines, dikes, and earth-dam batters).
More than half of India's cropland is losing
productivity because topsoil is being washed or blown away faster than natural
forces can replace it. Reducing the topsoil layer means reducing plants' access
to essential soil nutrients and water. For at least the next decade
environmental issues will dominate the agricultural and natural resource
sectors. Already the focus of much attention are the problems of deforestation,
increased flooding by major rivers, and reduced dry-season water flows for
irrigation and urban and industrial supplies. Not enough attention, however,
has been given to the massive problem of soil erosion and, more specifically,
to the need to reduce soil and water losses caused by excessive rainfall
runoff. Changes in farming practices have made the problem worse in recent
years. In response to the growing need for grain for exploding human and
livestock populations, farmers switched from traditional rotations and multiple
cropping to continuous-row cropping, a practice that encourages rainwater to
run off the land at a faster and more destructive pace. As a result crops are
denied the moisture they need for optimum growth (Truong and baker, 1998).
Results of numerous trial and mass applications of
Vetiver grass in the last 30 years in many countries show that the grass is
particularly effective in natural disaster reduction (flood, landslide, road
batter failure, river bank, irrigation canal and coastal erosion, water
retaining structure instability etc.), environmental protection (reduction of
land and water contamination, treatment of solid and liquid waste, soil
improvement etc.), and many other uses. The species of Vetiver System
originates in the state of Tamil Nadu, South India, which is now being promoted
in nearly 120 countries. It is a perennial bunchgrass of
the Poaceae family.
In western and northern India, it is popularly known as Khus. It
is sterile, non invasive and has to be propagated by clump subdivision.
Generally nursery multiplication of bare rooted plants is the preferred method.
The average multiplication rate varies but is normally, in a nursery, about
1:30 after about three months. Nursery clumps are divided into planting slips
of about 3 tillers each, and typically planted 15 cm apart on the contour to
create, when mature, a barrier of stiff grass that acts as a buffer and
spreader of down slope water flow, and a filter to sediment. A good hedge will
reduce rainfall run off by as much as 70% and sediment by as much as 90%. A
hedgerow will stay where it is planted and the sediment that is spread out
behind the hedgerow gradually accumulates to form a long lasting terrace with
Vetiver protection. It is a very low cost, labour intensive technology (linked
to the cost of labour) with very high benefit: cost ratios. When used for civil
works protection its cost is about 1/20 of traditional engineered systems and
designs. Engineers liken the Vetiver root to a "Living Soil Nail"
with an average tensile strength of 1/6 of mild steel.
What is Vetiver?
Vetiver
is most closely related to Sorghum but shares many morphological characteristics with
other fragrant grasses, such as lemongrass
(Cymbopogon Citratus), citronella (Cymbopogon Nardus, C.
Winterianus), and Palmarosa (Cymbopogon Martinii). It is a tall, tufted, perennial, scented grass,
with a straight stem, long narrow leaves and a lacework root system (Fig. 1)
that is abundant, complex, and extensive. It offers an inexpensive yet
effective and eco-friendly tool to combat soil erosion. The roots have been
used in Asia for centuries for their fragrance, and are woven into aromatic
matting and screens. The roots of some cultivars and ecotypes possess essential
oil that has been utilized as fragrant material since ancient times. The plant
also contains active ingredients used in traditional medicine and as botanical
pesticide.
The
Plant Vetiver belongs to the same group of grass family of rice, maize,
sorghum, sugarcane and lemon grass. It got its generic name Vetiveria, from its
Tamil name 'Vetiver' which means root that is dug up. Its specific epithet,
Zizanioides means 'the river side'. The fact is that the plant is commonly
found along the waterways. Its name was later reclassified as Chrysopogon
zizanioides. There are two types of Vetiver; one is seedling and the other is
non seedling. Seedling type is commonly found in North India, where as non seedling
variety is common in South India. Only the non seedling variety can be
recommended for any purpose connected with Vetiver, because the other variety
is able to spread unwantedly through seeds. The South Indian variety of Vetiver
has existed for centuries under cultivation and is widely distributed throughout
the continents. This variety can be propagated only through vegetative method.
SPECIAL
CHARACTERISTICS OF VETIVER GRASS
Morphological
characteristics:
•
Vetiver
grass does not have stolons or rhizomes. Its massive finely structured root
system that can grow very fast, in some applications rooting depth can reach
3-4m in the first year. This deep root system makes vetiver plant extremely
drought tolerant and difficult to dislodge by strong current.
•
Stiff
and erect stems, which can stand up to relatively deep water flow
•
Highly
resistance to pests, diseases and fire
•
A
dense hedge is formed when planted close together acting as a very effective
sediment filter and water spreader.
•
New
shoots develop from the underground crown making vetiver resistant to fire,
frosts, traffic and heavy grazing pressure.
•
New
roots grow from nodes when buried by trapped sediment. Vetiver will continue to
grow up with the deposited silt eventually forming terraces, if trapped
sediment is not removed.
Fig. 1: Multi-functioning and multi-dimensional
Vetiver system for the complete remediation of bio-environment
Physiological
characteristics
•
Tolerance
to extreme climatic variation such as prolonged drought, flood, submergence and
extreme temperature from -15ºC to +55ºC. The optimal soil temperature for root
growth is 25 °C. Root dormancy occurs
under a temperature of 5 °C. Shoot growth is affected earlier; at
13 °C, shoot growth is minimal, but root growth is continued at a rate of
12.6 cm/day. Under frosty conditions, shoots become dormant and purple, or
even die, but the underground growing points survive and can regrow quickly if
the conditions improve.
•
Ability
to regrow very quickly after being affected by drought, frosts, salinity and
adverse conditions after the weather improves or soil ameliorants added.
•
Tolerance
to wide range of soil pH from 3.5 to 11.0 without soil amendment.
•
High
level of tolerance to herbicides and pesticides.
•
Highly
efficient in absorbing dissolved nutrients such as N and P and heavy metals in
polluted water.
•
Highly
tolerant to growing medium high in acidity, alkalinity, salinity, sodicity and
magnesium.
•
Highly
tolerant to Al, Mn and heavy metals such as As, Cd, Cr, Ni, Pb, Hg, Se and Zn
in the soils
•
Vetiver’s
extremely deep and massive finely structured root system can extend down to two
to three meters in the first year. On fill slope, many experiments show that
this grass can reach 3.6m in 12 months. Vetiver 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.
•
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.
•
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.
•
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. (Truong et al, 1996).
•
This
grass re-grows very quickly following drought, frost, salt and other adverse
soil conditions when the adverse effects are removed.
•
Vetiver
displays a high level of tolerance to soil acidity, salinity, solidicity and
acid sulphate conditions (Le van Du and Truong, 2003)
Erosion control by Vetiver
Vetiver planting has been very effective in erosion control
or stabilisation in the following conditions:
•
Slope stabilisation along highways
and railways. Especially effective along mountainous rural roads, where the
community lacks sufficient funding for road slope stabilisation and where it
often takes part in road construction.
•
Dike and dam batter stabilisation,
reduction of canal, riverbank and coastal erosion, and protection of hard
structures themselves (e.g. rock riprap, concrete retaining walls, gabions, etc.).
•
Slope above culvert inlets and
outlets (culverts, abutments).
•
Interface between cement and rock
structures and erodible soil surfaces.
•
As a filter strip to trap sediment
at culvert inlets.
•
To reduce energy at culvert outlets.
•
To stabilize gully head erosion,
when Vetiver hedges are planted on contour lines above gully heads.
•
To eliminate erosion caused by wave
action, by planting a few rows of
Vetiver on the edge of the high water mark on big farm dam batters or
river banks.
•
In forest plantations, to stabilize
the shoulders of access roads on very steep
slopes as well as the gullies (logging paths/ways) that develop
following harvests.
Benefit of Vetiver Grass
§
A permanent, low maintenance
solution: Vetiver grass is a perennial plant, which provides a permanent
solution with little or no maintenance
§
Strong anchors are spread evenly
over the stabilized area: The Vetiver root mass is very large and the fibrous
roots are very strong
§
Deep anchorage: Vetiver roots
penetrate several meters into native soil or fill material
§
A durable surface: Vetiver foliage
is tough, it survives fire and extended flooding
§
Stops soil erosion: The dense
foliage traps soil particles being washed downhill
§
Improves water quality: Sediments
are trapped by foliage before entering nearby waterways
§
Water harvesting, flood mitigation:
Vetiver greatly increases percolation rates
§
Supports local economies: Vetiver
projects are labor intensive. They employ locals, especially in rural areas
§
A ‘Green’ solution: Vetiver is more
natural and more attractive than stone or concrete
§
Side-benefits: Vetiver foliage may
be harvested for thatching, fodder, composting or other purposes where biomass
is required
Risk Assessment
§
Vetiver is non-invasive: It sets
sterile seed and does not have running stolons
§
Vetiver is non-competitive: Roots
grow vertically downwards, vetiver does not compete with adjacent plants
§
Safe from pests and disease: Vetiver
has been shown to have very few pest or disease problems
§
Precedents: Vetiver has been proven
in many projects in many countries around the world. Vetiver has been promoted
and supported by the World bank for many years
Advantages:
•
The
major advantage of VS over conventional engineering measures is its low cost
and longevity. For slope stabilisation in China, for example, savings are in
the order of 85-90% (Xie, 1997 and Xia et al, 1999). In Australia, the cost
advantage of VS over conventional engineering methods ranges from 64% to 72%,
depending on the method used (Braken and Truong 2001). In summary, its maximum
cost is only 30% of the cost of traditional measures. In addition annual
maintenance costs are significantly reduced once Vetiver hedgerows are
established
•
As
with other bioengineering technologies, VS is a natural,
environmentally-friendly way to control erosion control and stabilize land that
‘softens’ the harsh look of conventional rigid engineering measures such as
concrete and rock structures. This is particularly important in urban and
semi-rural areas where local communities decry the unsightly appearance of
infrastructure development.
•
Long-term
maintenance costs are low. In contrast to conventional engineering structures,
green technology improves as the vegetative cover matures. VS requires a
planned maintenance program in the first two years; however, once established,
it is virtually maintenance-free. Therefore, the use of Vetiver is particularly
well suited to remote areas where maintenance is costly and difficult.
•
Vetiver
is very effective in poor and highly erodible and dispersible soils.
Disadvantages:
•
The
main disadvantage of VS applications is the Vetiver’s intolerance to shading,
particularly within the establishment phase. Partial shading stunts its growth;
significant shading can eliminate it in the long term by reducing its ability
to compete with more shade-tolerant species. However, this weakness could be
desirable in situations where initial stabilisation requires a pioneer to
improve the ability of the micro-environment to host the voluntary or planned
introduction of native endemic species.
•
The
Vetiver System is effective only when the plants are well established.
Effective planning requires an initial establishment period of about 2-3 months
in warm weather and 4-6 months in cooler times. This delay can be accommodated
by planting early, and in the dry season.
•
Vetiver
hedges are fully effective only when plants form closed hedgerows. Gaps between
clumps should be timely re-planted.
•
It
is difficult to plant and water vegetation on very high or steep slopes.
•
Vetiver
requires protection from livestock during its establishment phase.
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