Slope Stabilization and Protection
Vetiver Grass (Chrysopogon Zizanioides) when implemented correctly as a bio-engineering tool according to the Vetiver System (VS) offers a simple, green and cost-effective tool to assist the stabilization and protection of sloping land, road embankments, etc. The deep and fibrous vetiver root system extends deep into the soil, reinforcing the soil structure, thereby stabilizing the surrounding slopes. As opposed to different types of grasses whose roots are fairly shallow and sometimes grow horizontally, vetiver grass roots grow vertically, as much as ten (10) feet deep and with a tensile strength equivalent to 1/6 mild steel reinforcement, growing in a wide range of soil conditions and penetrating even the toughest soils.
During high rainfall events, surface water picks up speed as it runs off the land causing erosion of soils, and as total flow speeds and volumes increase this can get quite severe causing loss of soils and eventually loss and damage to land, private property and infrastructure. When vetiver plants are installed in horizontal rows on contour perpendicular to the flow of surface runoff, and are able to successfully establish to form continual dense hedgerows, erosion can be diminished or prevented all together. This is made possible since at each hedgerow, water runoff is forced to stop and take its take to percolate through the thick and dense vetiver leaves, spreading out across the contour will dissipating and losing speed. The deep and fibrous roots also bind loose dirt, securing the soil both above and below ground.
Furthermore, topsoil being transported in the runoff water is deposited behind the vetiver hedgerows, ‘repairing’ any existing small-scale erosion gullying which may have been taking place before. For major and severe gullying which has taken place over time, Vetiver System (VS) solutions often need to be combined with other measures in order to successfully repair the gullies – such as check dams, gabion baskets, or earthworks to carry out needed terra-reformation prior to VS installation.
With its extremely deep and fibrous root system, which grows vertically and not laterally, vetiver grass has an enhancing effect on concrete infrastructure by protecting the soil-concrete interface. Common examples of this benefit may be along the edges of roads, drainage channels, riverbanks, retaining walls, bridge abutments etc. Where it is common for soil erosion to take place over time and compromise these structures, in some places leading to their failure and collapse; vetiver grass binds the soil together to protect and prevent any such washout from taking place – keeping soil intact around infrastructure and helping to improve their overall resilience and longevity.
Surface Water Management
As part of the solutions design process, Vetiver TT EES Ltd brings critical water management considerations and recommendations to ensure project success. Where the Vetiver System (VS) provides a medium to long term solutions, in the short term during intense rains if not managed correctly surface water runoff can cause a lot of damage to soil, land property and infrastructure. We therefore offer both short term and long term water management solutions; where in some cases only temporary water management is required until the VS is established. Short term water management can comprise of plastic or geotextile lined surface channels, and other means. Permanent water management measures include grass or gravel lined drains, concrete drainage, subterranean ‘french-drains’, etc. We offer design and implementation of all of these solutions, combining with the Vetiver System (VS), and where applicable other measures such as gabion rock baskets, and other appropriate tree and vegetation species.
The Vetiver System (VS) itself, once established also assists with water management, since runoff water is slowed down dramatically and ‘spread out horizontally’ by hedgerows on contour. If correctly implemented and maintained until established, this effect can eliminate many of the damaging effects of surface water, by combining the effects of vetiver roots to prevent soil erosion with the spreading out and slowing down of rainfall runoff. This also has the benefit of promoting natural groundwater recharge, which can create more fertile and healthier lands during dry periods, and can alleviate the effects of flooding or erosion damage to other properties downstream.
Soil and Water Conservation
Vetiver hedgerows when established on contour are able to significantly slow down the rate of surface runoff on gently or steeply sloping hillside watersheds alike. The reduction in flow velocity is able to reduce and prevent soil loss due to erosion, where the hedgerows themselves capture loss sediments and soils forming ‘natural terraces’ behind them over time.
Moreover though, very importantly for degraded and de-vegetated watersheds, during heavy rainfall events surface water moves downhill very quickly since there is no vegetation to reduce its flow, entering valleys below and contributing to flooding. By successfully establishing several vetiver hedgerows on hillside watersheds, the overall rate of runoff can be effectively reduced with the water flow speed being brought to zero (0) m/s at each hedgerow, effectively changing the hydrology of the watershed and reducing the rate at which water exits hillside lands. This contributes to groundwater recharge since rainfall runoff can stay in contact with the soils for a significantly longer period of time, and as a result, can also assist and reducing flooding in low lying areas if implemented at a large enough scale.
Higher groundwater levels result in rivers and streams flowing for a longer period of time into the dry season months, and greater soil moisture allows natural vegetation or farm crops to thrive better as periods of dry weather set in.
The Vetiver System (VS) can be used for land rehabilitation. It is a cheap alternative compared to traditional methods, though is most effective when implemented in a ‘preventative’ way, where it is apparent that landslides are beginning or could potentially occur. After major landslides have already taken place, the VS can also be an incredibly useful tool in the stabilization and rehabilitation process; however if they are too severe, often combined solutions may be required where recommended designs may entail the Vetiver System (VS) along with other traditional methods such as geotextiles, gabion baskets, etc.
To prevent landslides or rehabilitate existing slips from further movement, the fibrous roots of the vetiver plant penetrate deep into the ground, surpassing the slip surface for cases less than three (3) meters deep. This action changes the overall shear strength of the slope, essentially providing a reinforced soil structure, and has been proven to increase overall slope stability by up to 40%. This can play a major role in preventing future landslides from occurring.
Vetiver Education & Empowerment Project (VEEP)
The Vetiver Education & Empowerment Project (VEEP) is a unique knowledge sharing model which was first developed working in the Paramin Community, Trinidad, alongside the Paramin Development Committee (PDC) and the GEF Small Grants Programme supported by the UNDP. Through VEEP, the Vetiver System (VS) is introduced to communities as a simple, cost-effective and easy to implement bioengineering tool which can be used by anyone (especially farmers whom work so closely with plants), to protect their roads, homes, infrastructure, and agricultural lands.
Rehabilitation of Degraded Lands
The Vetiver System (VS) can serve as a valuable pioneer species and solution to aid with the rehabilitation of degraded lands. These can include: Quarries and mines, devegetated and degraded hillsides, construction projects where land has been cleared of all vegetation and topsoil, and contaminated lands and water such as landfill environments, leachates, and industrial and sewage waste water contaminated sites.
The VS can aid with rehabilitation of these environments in the following ways:
- On hillside terrain, vetiver hedgerows slow down rainfall runoff, reducing erosion and capturing loose topsoil and sediments – which prevents further soil and land damage, and can also help to build back valuable organic matter in the soil. Over time, natural terracing can also take place behind vetiver hedgerows as topsoil accumulates.
- By slowing down rainfall runoff, water gets to spend greater time in contact with the ground especially behind the hedgerows, percolating into the soil, increasing soil moisture and promoting groundwater recharge. Accompanying the captured topsoil and sediments accumulating behind hedgerows, this can lead to fertile environments for other plants to grow.
- Vetiver hedgerows also tend to capture seeds of native species behind them, which find a healthy environment to grow given accumulation of topsoil and soil moisture. It is therefore common to see local shrubs and trees to begin springing up behind hedgerows within 2-3 years of establishment. Vetiver grass planted in this formation thus becomes a ‘pioneer’ species, which in fact assists with the subsequent regeneration of land by native or indigenous species.
- With their deep roots, vetiver grass extracts nutrients from the deeper layers of soil as well as moisture during dry times. It accumulates a lot of this in its leaf biomass, which can be cut regularly and placed on degraded land as mulch. Very high in carbon, vetiver leaves can decompose over time to build back healthy topsoil, while also acting as a soil cover and helping to conserve moisture.
- Vetiver grass is a proven phytoremediator, and can absorb high levels of contamination including nutrients and heavy metals, thus lowering the toxicity of land and helping it return to natural and acceptable levels. Click here to learn more about vetiver use for phytoremediation of contaminated lands and waters.
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