Monday, January 18, 2010
Elise Pinners who lives and works in Kenya has found that even with all the literature that is available, many people, including scientist do not understand the technology nor do they apply it correctly. Most frequent misapplications include planting too far apart within the line and planting on existing terrace ridges, the latter completely misses the point that a vetiver hedgerow acts as a permeable buffer, spreader of rainfall run off, and a trapper of soil. Elise has created a very useful comparative table showing the differences between a vetiver hedgerow and a constructed terrace, in her case Kenya's "Fanya Juu" system of conservation.
One aspect of vetiver that people either don't know about or disregard is that it is very different from other conservation plants and grasses in its root development. I know of no other grass that develops new roots from the culm and branches as sediment gets trapped behind it. See P.K Yoon's photo 1 below.
Photo 1 (P.K.Yoon)
This feature enables vetiver to recover from deep sediment collection (as after extreme flooding with high sediment loads), and allows it to grow as a complete hedge and at the same time creates its own terrace riser. This creates terrace risers as in photo 2a. Note the vetiver was originally planted along the bottom of the terrace.
Photo 2a - (John Greenfield)
Photo 2b - (John Greenfield)
Photo 2b. shows the top of the terrace behind the hedgerow shown in Photo 2a. Note how this 20% original slope now has a reduced slope due t sediment capture. This in itself will reduce water velocity and erosion.
Photo 3 - vetiver planted across a gully/drainage line in Natal, South Africa, was impacted by a huge storm (over 300 mm of rain) that washed out soil from a neighboring unprotected farm. The vetiver was 1.5 m high and trapped up 75 cm of soil behind it. Most other plants would have never survived, and would have been flattened. Vetiver withstood the flood and trapped the soil and created a new "growing base level" at the sediment top. This is very unique and is why in photo 4 this 30 year old vetiver protected gully in Fiji looks so good and has been nearly filled up with vetiver trapped sediment.
Photo 3 - left (John Greenfield)
Photo 4 (John Greenfield)
Photo 5 from Jano Labat's farm in Zimbabwe shows a 2 year old vetiver hedge across a depression. Note the following: 1. The vetiver hedge is dense (due to correct planting). 2. sediment and water is collecting behind the hedgerow in its lowest area. This will over time become a level area right across the upper side of the hedge row. 3, the water backs up and ponds 4-5 meters back. This water will disperse through: infiltration in front of the hedge (where ponded), at the hedge itself (improved infiltration because of the penetrating roots), and (photo 6) below the hedge row as it oozes through. Photo 6 below the hedge - the water has been trapped by an additional hedgerow below the first. But notice how the water is spread out right across the depression, partly because the first hedge spread the water out.
If these hedges were not in place, most of this water and more would have been added to flood flow discharge into downstream drainage and would have been lost.
Photo 5 (Grimshaw)
Photo 6 - (Grimshaw)
This PLANT is unlike any other, no wonder in Ethiopia, where planted CORRECTLY the results are good, farmers are benefitting and wetlands are being restored. We have to get this message out to our farmers and to the folks who advise them.
One last thing. This technology also works on slopes of less than 1%. "Flat" lands flood and erode, and need just as much protection as steeper slopes. This is nicely demonstrated in Paul Truong's work on the black soil flood prone Darling Downs, Queensland. Australia. Photo 7. note the sediment collected behind the hedgerow. Thus vetiver is not only a soil conservation management tool, but also a WATER management tool.
Photo 7 - (Paul Truong)
ONE last point for the scientists is that when comparing vetiver hedgerows with other species on the standard 10 x 3 m runoff plots over one or two years is not very good science because (1) vetiver performs better with age, and (2) most comparative plants do not have similar longevity and general reduce performance with age!! In addition in real life rainfall runoff velocity and intensity is often quite different because runoff water does not occur the same across the field as a whole but is often naturally directed into areas that concentrate runoff creating rills that carry water at greater velocity. If scientists want to research and compare different hedgerows comprising different plants, the plot size should be at least quarter hectare in area. If this is done then very different results will be created.
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Useful gallery of all blog images (with captions) posted on Picassa