Sunday, April 19, 2009

Vetiver! Now there's a plant you can take to the (em)Bank!

During the last couple of months, I've met many people on Oahu who were affected by the December flooding. Mother Nature's handiwork is pretty remarkable. She quickly carved out huge hunks of earth, displaying none of her typical finesse. Owners of property adjacent to waterways lost as many as 15 feet of land. Dwellers in the affected areas cleaned up silt and debris for weeks. I don't need to tell Hawaii residents that the dirt ultimately landed in the ocean. The governor declared a disaster and a flood of federal money was finally released. Now's the perfect time to take a measured approach to stabilizing our banks--not only the multinational institutions that profited mightily while ruining our economy, but the embankments that protect our waterways and ensure that our homes remain "flood-free" areas.

Not surprisingly, Dick Grimshaw has wise perspective on the subject. Refreshed after his recent trip to Africa, where farmers still sing praises to the World Bank agronomists, like Dick, who introduced them to the Vetiver System more than 20 years ago, he shares some prescient observations:

We face major economic and environmental problems from river bank erosion and the collapse of dikes and levees. Climate change accelerates these changes by bringing extreme wind and rainfall events. Although many people are familiar with the Vetiver System and have carefully studied the supporting research data and results of actual site applications and promote its use to stabilize water-related structures, others find it difficult to accept the fact that Vetiver is uniquely suited for such purposes. The latter normally cite three main reasons for not using Vetiver: (1) a preference for native plants; (2) fear that Vetiver will escape and invade the environment, and; (3) other species are better suited to slope stabilization.

Let me address these concerns.

1. Native plant preference. If native plants can solve the problem at reasonable cost and for the long term, we certainly support their use. Remember, though, that native plants typically are very site specific, and perform well under some conditions. They generally cannot withstand the wide range of challenges posed by a particular site, including prolonged flooding, wave action, erosion, changes in soil composition, human activity and misuse.

2. Vetiver might become invasive. All evidence suggests otherwise for cultivars of Chrysopogon zizanioides that have been derived from the south Indian non-fertile Vetiver. These cultivars are named "Sunshine," "Monto," "Karnataka," "Silent Valley," and others. DNA research performed by Adams and Dafforn clearly link these cultivars as a single clone that is widely used throughout the tropics, and are all non-fertile.

The USDA Forest Service maintains a risk assessment data base called Pacific Island Eco-system at Risk (PIER). Applying 50 criteria, this data base classifies all potentially risky plants based on their potential for invasiveness. Plants with ratings of 1 or less are acceptable. Vetiver's rating is -8, the lowest risk of invasiveness. Compare Vetiver's rating with some other plants commonly used for soil conservation and bank stabilization:

Bahia grass (Paspalum notatum) Rating 18
Bermuda grass (Cynodon dactylum) Rating 5
Elephant grass (Pennisetum purpureum) Rating 18
Guinea grass (Panicum maximum) Rating 17
Kikuyu grass (Pennisetum clandastinum) Rating 18
Rhodes grass (Chloris gayana) Rating 18
Switch grass (Panicum virgatum ) Rating 11
Vetiver grass (Chrysopogon zizanioides) Rating -8

You can review these ratings and those of other species at:

3. Choice of species for river and levee stabilization. River banks collapse because of current damage, wave action, the wetting and slumping of non-cohesive soils and/or by piping caused by the rotting of dead lateral tree roots. A cardinal engineering rule is not to allow trees to grow on embankments next to water. Past designs for bank protection have included rock and rip rap or a combination of rip rap and turf grasses such as Bahia grass. However, under extreme flooding and storm conditions, these measures have failed quite dramatically and expensively. On the other hand, the Vetiver System is an effective alternative. Forty provinces in Vietnam now use VS to stabilize sea dikes and levees, with a high degree of success and at great cost savings. Research underlying this work has been completed by the Vietnamese and by Delft University of Technology in the Netherlands, one of the world's leading centers for hydraulic research.

Let me quote some concluding remarks of the study entitled "Vetiver Grass for River Bank Stabilisation" by D.J. Jaspers-Focks and A. Algera, Delft University of Technology, C.B. van Bossestraat 11, 5612 SC Eindhoven, The Netherlands (

Vetiver grass is a sustainable and innovative solution to protect river banks and dikes. It thrives under a wide variety of conditions. Although growth rates are lower with a high groundwater level, it still thrives around the SWL, in contrast to sod-forming grasses. This clearly shows that Vetiver can be used at SWL as well as on dikes where the phreatic level can be low.

Vetiver is able to establish a full-stop of bank erosion caused by rapid drawdown. Therefore it provides us with strong indications that it is highly suitable as an anti-erosion measure. A combination of cohesive soil and Vetiver provides the best protection against erosion, which implies that it is highly suitable for banks in delta areas, which consist predominantly of cohesive soil.

A single hedge of Vetiver planted on the outer slope of a dike can reduce the wave runup volume by 55%, in contrast to sod grasses that provide no reduction. Planting multiple hedges along the contour of the outer slope might result in even more reduction. Installing Vetiver on existing dikes may substantially reinforce them.

The advantages of Vetiver over conventional methods with the use of stone are many:

Vetiver is not invasive and no significant diseases are known. Vetiver will, in contrast to traditional methods, increase in strength over time. Vetiver is an economically attractive solution. In most Southeast Asian countries countries Vetiver can be planted cheaply, while solutions consisting of stone and concrete are expensive in delta areas.
Vetiver allows people to protect their own property. Since its cost is low and it is easy to use, local initiatives can be easily achieved.
Vetiver can be an aesthetically good solution and is a socially-acceptable solution for bank protection.

This research study also found:

Influence of soil type and phreatic level on Vetiver:

* Cohesive soil reduced the growth rate of Vetiver by approximately 50% compared to a noncohesive soil, which is significant. Further, a decrease in phreatic level of 0,17 m resulted in significantly higher growth rates, in the order of 10-20%.

Vetiver as bank protection against vessel-induced loads:

* The influence of Vetiver on small scale mass failure was tested using a physical model test. The drawdown caused by passing ships was reproduced using a wave flume. The amount of eroded material of cohesive soil (clay) was approximately 8-10 times smaller using Vetiver. The erosion of non-cohesive soil was also reduced dramatically. A combination of cohesive soil and Vetiver had the lowest amount of erosion and, after approximately 800-1000 cycles,the erosion fully stopped.

Given its high evaporation rates, Vetiver in hot climates can act as a pump to remove excess water in embankments and thus reduce hydraulic pore pressure in the soil. The likelihood of slope collapse increases significantly when hydraulic pore pressure increases. Add to this Vetiver roots' high tensile strength (4-6 times greater than Bahia and other grasses), and we have a very formidable and useful plant for slope stabilization.

Although other nations are using VS applications, I remain very concerned that Vetiver's potential is not being exploited here in the United States. We certainly recognize that people have different agendas. However, although the profitability of using hard engineering techniques is much higher and undoubtedly more attractive to the designer and vendor, it's not to the taxpayer who ultimately shoulders the cost of porkbarrel or ill-conceived Federal and state projects, as well as the cost of their damage and failure.

The greatest block to wider use in this country is the unfounded fear that Vetiver might become an invasive plant--which it most definitely is NOT--and an often deliberate neglect and even scorn of good science (of which there is A LOT) by people who should know better and who fail to properly investigate the true value of this remarkable plant and its applications.