VETIVER AND COASTAL EROSION€¦ · environments makes it especially effective and applicable for coastal erosion. Vetiver ... HALF SEA WATER Although Vetiver has a ... soil and water

www.veticon.com.auCopyright Veticon Consulting PTY LTD 2017

V E T I V E R A N DC O A S T A L E R O S I O N



COASTAL EROSIONThe erosion of coastlines and waterways is a natural process through wave action, current energy, winds and storm surges, which create natural fluctuations of coastlines as the sediment supply is moved along coastal foreshores and waterways. High tides, winds and storm surges result in a rise in the sea level, which makes beaches and dunes susceptible to the power of incoming waves. With the down rush of the waves, sand is dragged out to sea, causing erosion to beaches and dunes. This process also serves to weaken the dunes, making them more vulnerable to collapse and further erosion. The natural process allows for sand to be returned to the beach, however, these natural fluctuations are becoming heightened with the impacts of climate change and human interference. Climate change is causing a rise in sea levels, combined with more frequent and powerful storms, which make coastal regions increasingly vulnerable to erosion.

The natural ebb and flow of coastlines starts to become a problem in urbanised coastal zones, whereby erosion begins to impact the utilisation of beaches and the developments within the erosion zone. The increased human activity and developments along coastal areas limits the coastline’s ability to adapt to the natural change process, no longer can the coast accommodate the natural process of erosion, as there is no capacity for the coastline to retreat inland.

Human habitation of coastal areas place sharp constraints on the natural environmental system and as a result, we now need to consider the causes and impacts of coastal erosion. In order to ensure long-term environmentally harmonious and resilient protection of our coastlines, we need to identify solutions for sustainable management and risk reduction.

Vetiver beach application - planted in sandbags


COASTAL EROSION INTERVENTIONS

Traditional hard engineering methods of protecting coastlines against erosion, such as breakwaters, jetties, groynes and rockwalls may serve to protect some areas of the shoreline, however, they have adverse effects on sand flows, causing and accelerating erosion down the coastline. They can also be severely impacted by storm damage, requiring consistent maintenance and redesigns. When considering options for resilience planning and coastal protection, both the long and short-term effects need to be considered. Not only the environmental impacts but also whether the action plans are in the long-term economically viable and sustainable.

Vetiver provides an environmentally harmonious, long-term workable solution, whether used alone or in conjunction with other engineering protection mechanisms. Vetiver has the capacity to act as a reinforcement system for dune and beach protection.


VETIVER GRASSVetiver (Chrysopogon zizanioides) is a fast growing perennial grass with a vast interlinked root system and strong stems, which together create a miracle plant with the capacity to address a multitude of environmental and engineering needs. Vetiver System applications create living walls, filter systems, and act as “live nail” reinforcements.

WHY VETIVERThe combination of these unique characteristics makes Vetiver exceptionally effective for soil bioengineering and coastal erosion protection and stabilisation:

• Stiff and erect stems create dense hedges withstanding high velocity flows, trap sediment, and control water runoff, protecting against erosion

• Deep, extensive and interlocking root system that grow vertically reaching depths of 5+ metres, creating dense underground reinforcing root wall structures

• Strong roots with a tensile strength of 75Mpa equivalent to1/6th of mild steel

• Roots improve soil sheer strength by 45%

• Thrives in a variety of soils; sandy, sodic, saline, water logged, acidic, alkaline and toxic contaminants

• Tolerant to climatic and environmental variations; drought, flooding and submergence, and air temperatures of -15C to 55C

• Roots develop from nodes, if buried, so Vetiver rises with the ground level

• Roots create favourible conditions for soil microbial activity, which improves soil fertility. Allowing Vetiver to create favourable conditions for land regeneration and reforestation


VETIVER AND SALT TOLERANCEThe unique resilience of Vetiver grass and its ability to survive in saline soils and environments makes it especially effective and applicable for coastal erosion. Vetiver’s saline threshold level is at ECse = 8dSm-1, and Vetiver can survive at 47.5 dSm-1 under dry land salinity conditions. When considering the coastal application of Vetiver, seawater has an ECse of about 45 dSm-1. ECse = measurement of water and/or soil salinity.

HALF SEA WATER

Although Vetiver has a high tolerance to salinity, it does not survive below the high tide level. Therefore, in application of Vetiver in areas close to high tide levels, it is beneficial to use it in combination with other salt tolerant plants or protected by hard structures, which Vetiver acts to support and reinforce.

VETIVER FOR COASTAL EROSION:• Stabilises, strengthens and protects soil• Withstands storm surges• Traps sediments• Improves soil biodiversity, assisting in natural revegetation• Stops and reverses erosion• Sustainable long-term solution• Environmentally harmonious


VETIVER SYSTEM FOR EROSION CONTROL AND PROTECTIONThe application of Vetiver as a bioengineering tool in water-based situations, for stabilisation, protection and disaster mitigation, has been utilised across the world. Including for beach, estuary and riverbank erosion control and stabilisation in Australia, Brazil, Venezuela, China, the Philippines, India and Vietnam.

Extensive research and development has resulted in the Vetiver System, which plants Vetiver in rows, forming strong and dense hedges. It is the application of Vetiver hedgerows and the unique characteristics of Vetiver grass which make it exceptional for erosion control and stabilisation.

slipping zone on slopes

usually 0~2 m depths

Vetiver roots

Vetiver hedgerows

Monto Vetiver Grass

The protective effects of Vetiver System hedgerows for erosion and sediment control can clearly be seen in the below image of Vetiver road batter stabilisation and protection in Mackay, Queensland. The Vetiver hedgerows successfully reinforced and protected the soil against erosion.


HOW THE VETIVER SYSTEM WORKSVetiver’s unique characteristics combine to work simultaneously above and below the ground to ensure erosion control, soil and water conservation and steep slope stabilisation, giving it the capacity to withstand floodwaters, and storm and wave surges.

ROOTSBelow the surface the dense, deep and penetrating root system of Vetiver grass can reach vertical depths of 5+ metres, binding and reinforcing soil shear strength by up to 45%. The roots are extremely fine and strong with a tensile strength of 75 MPa, which is equivalent to approximately 1/6th of mild steel reinforcement.

When planted in hedgerow format, due to its clonal nature, the roots of the plants grow and interlock, creating vast underground, dense and strong root wall systems, which serve to bind, stabilise and increase the tensile strength of the soil. Protecting against erosion, instability and flood disasters.

STEMSThe strong, thick and stiff stems create above ground hedges, which protect the topsoil by dissipating wind and water energy, slowing down water flow, trapping sediment and controlling water runoff. These hedges act to protect the topsoil, ensuring that it remains in place and overtime, create natural barriers to flow by trapping soil and sediments.

RESILIENCEA resilient and adaptable grass, Vetiver is disease and pest resistant, can recover after fires, and withstands prolonged periods of flooding and drought, surviving in air temperatures of -15C to 55C. Vetiver can grow and thrive in a variety of soils: sandy, sodic, saline, waterlogged, acidic, alkaline and toxic (from pH 3.3 – 12.5). Most importantly, Vetiver grass is sterile, it has no above or underground runners, which means it has NO WEED POTENTIAL, allowing for Vetiver to be shaped and applied for specific use without the threat of it spreading or competing with other vegetation.


CASE STUDYCOASTAL EROSION PROTECTION BRAZIL

THE ISSUE:Coastal erosion caused by high tide waves and hurricane induced storm surges.

INITIAL INEFFECTIVE ATTEMPTS AT EROSION CONTROL:A native grass, sweet grass (Paspalum maritimum) that is very common in most of Brazil’s coastal zones and easily established, was applied for protection against erosion.

SECONDARY ATTEMPTS AT EROSION CONTROL:Riprap using raffia bags filled with a mixture of soil and cement (12% cement and 88% local soil) was applied. Although this measure partially worked, it was abandoned in search of a more aesthetic and environmentally friendly option.


THIRD ATTEMPT AT EROSION CONTROL:Following the failure of sweet grass and the desire for an environmentally harmonious method for erosion protection, specific guidelines were established.

The requirements for the beach protection were:• Sustainable technology • Low establishment costs• Low operating and maintenance costs• Environmentally green

The following hard engineering methods were considered but were rejected due to high costs and unsustainability:• Rock riprap• Rock mattresses• Rock groyne• Concrete pile wall

Bioengineering methods were also considered:• Native vegetation, Marram and Sweet Grass – Sweet Grass was rejected due to its previous failure and Marram grass was rejected, as it is not effective in protecting eroding sandy beaches• Vetiver grass through the application of the Vetiver System was the chosen and successful method

SUCCESSFUL VETIVER GRASS APPLICATION:

The choice was made to apply the Vetiver System, utilising cocologs in low risk areas and wooden palisades in high-risk areas to increase the security factor of the structure, anticipating sea level rise due to climate change in the future.

The planting of Vetiver grass, associated with sediment retainers and biodegradable blankets was very successful. It was a low cost and effective technique to control erosion and prevent landscape destruction during strong surf and high tides. The strong, deep and penetrating roots of Vetiver allowed it to bide the coastal sandy soil. Vetiver also proved its tolerance to long-term exposure to salinity.


4 months after planting 4 months growth

SUCCESFUL PROTECTION AGAINST STORM SURGES:

Within only 6 weeks of planting, the beach experienced major sea storm surges, which led to strong surf and waves hitting the site. These storm surges damaged the Vetiver plants in the first hedgerow but although badly damaged, they recovered naturally.

Though there was some damage to the Vetiver, it effectively protected the soil during these surges. There was NO soil loss in the first 3 Vetiver rows at the worst area where the waves hit.


LONG–TERM EFFECTS OF VETIVER APPLICATION:

Two years after installation, re-colonisation of native vegetation of herbaceous grasses show the quality of the recovery process of the site, with soil biodiversity and stability.

The stability of the site nine years after implementation has proven that the Vetiver System is a very sustainable and green solution to the beach erosion problem along the Brazilian coastline.

10 months after planting (2010)7 months after planting (2009)

3.5 years after planting (2012) 6.5 years after planting (2015)

THE APPLICATION OF THE VETIVER SYSTEM PERFORMED THE FOLLOWING:

• Protected the beach and coastline• Halted Erosion• Improved soil biodiversity and stability, assisting in the re-establishment of native vegetation.


Complete integration with the beach landscape

WHY NOT USE NATIVE PLANTS:As environmental awareness has evolved, the desire to utilise indigenous plants where possible has developed. However, local native plants are mostly adapted to a low fertility, unpolluted and clean Australian environment. Therefore they generally cannot be used for land stabilisation purposes on artificially disturbed sites, as they do not have the unique attributes of Vetiver, such as:

• Tolerance to extremely adverse growing environments: ➢ High soil salinity, acidity and alkalinity conditions ➢ Heavy metal contaminants and agrochemicals such as weedicides and soil amendments ➢ Prolonged drought and inundation• Penetrating, long and extensive root system• Highly adaptable to various soil types, from beach sand, and heavy clay to decomposing rocks

Vetiver is a sterile grass, it has no above or underground runners, which means it has no weed potential and cannot self-spread. Therefore, it poses no threat to the environment and other vegetation, both native and introduced species.

Strong current flattened the native grass but not Vetiver on this waterway


Lomandra a native plant commonly found on the edge of drainage lines and watercourses in Queensland and NSW. There are two species; the taller and more erect Lomandra longifolia is commonly used in Australia for erosion control and stabilisation. The shorter Lomandra hystrix is not commonly used. Lomandra is of the sedge family and thus is shallow rooted and normally grown in a wetter environment. As a native species it does possess properties making it adaptable to Australian climatic conditions, however when compared with Vetiver, it is inferior for effective erosion control and stabilisation.

VETIVER COMPARED TO NATIVE LOMANDRA

Shallow rooted Lomandra - roots grow up to 30cm

LOMANDRA COMPARED TO VETIVER

LOMANDRA VETIVER

ROOTS

- Shallow roots, grow to depth of

about 30cm

- Improve soil shear strength by 50%

but only to the depth of the roots

- Deep roots, grow to depth of 5+

metres

- Improve soil shear strength by

45%

- Tensile strength of 75Mpa

equivalent to1/6th of mild steel

SOIL

- Grows in sandy, sandy loam & clay

soils

- Best growth in pH neutral soil (6.5 –

7.5)

- Commonly grows in non-saline soils

- Moist, well-drained, moist

moderate drainage

- Thrives in a variety of soils; beach

sand, and heavy clay to

decomposing rocks

- Survives in sodic, saline, water

logged, acidic, alkaline and

toxic soils

- Grows in pH 3.3 – 12.5 soils

STEMS - Blades grow up to 1.2 metres high

- Perennial tufted

- Blades can grow up to 3 metres

high

- Perennial tufted

- Can resist high velocity water

flows, up to 5 metres per second

TOLERANCE

- Moderately drought tolerant

- Can survive in temperatures of -10

to 31C

- Drought, flooding and

submergence tolerant

- Survives in air temperatures of

-15C to 55C

ISSUES

- Does not like prolonged wet

conditions

- Cannot withstand high rainfall and

flooding conditions

- Does not like overshading


THE SANTOS ROMA HUB BLYTHE CREEK CROSSING

This is AFTER the rehabilitation attempt – the lomandra died off through the dry months and also cattle grazed all the grasses (Rhodes etc), and damaged the jute mesh.

ADVANTAGES OF VETIVER• Sustainable• Non-invasive• Environmentally harmonious • Stabilises and strengthens soil• Slows water flow, allowing for proper water infiltration • Can withstand water flows of 5m/sec• Long-term solution: gets stronger as it grows• Traps sediments• Exceptional resistance to high velocity water flows – thrives through storm seasons• Carbon sequestration (estimated 150 tons per hectare per year)• Erosion control – above and below the surface• Drought tolerant• Survives flooding• Improves water quality – nutrient and toxic contaminants removal • Aesthetically appealing • Creates grassland habitat for wildlife • Minimal ongoing maintenance costs (compared to hard-armour methods)

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COPYRIGHT VETICON CONSULTING PTY LTD 2017

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VETIVER AND COASTAL EROSION€¦ · environments makes it especially effective and applicable for coastal erosion. Vetiver ... HALF SEA WATER Although Vetiver has a ... soil and water