Thursday, March 15, 2007
I was recently (February 2007) visiting Hawaii. Vetiver grass (sterile non-invasive Sunshine cultivar) has been approved by USDA for use on the Islands and has been tested successfully on some of the old Delmonte pineapple farms. Hawaii's climate is similar to Fiji and tropical China (Guangdong Province) where the Vetiver System has been used extensively.
When driving north along O'ahu's windward coast I came across an area of coastal water that was carrying high sediment loads from nearby coastal land. The Google Earth image (June 2004) shown in this blog shows the outflow sediment fans from two rivers (red arrows). Note in February the sediment discharge was even higher due greater rainfall and runoff at this time of year. This sediment is then moved up and down the coast line, damaging coral and fish. Inland is an area of about 1000 acres, approximately half of which is not under forest or other ground cover, that appears to be the main source of this sediment. Marked on the image are a few of the point source erosion sites. (A) beach erosion - probable removal of mangroves; (B) tree removal and what appear as possible land terrain vehicle damage:(C)unprotected crop land (D) and (E) road erosion. (None of these points have been ground truthed, but nethertheless are clearly contributing to the sediment flow to the sea).
These sediment problems could be easily resolved through the application of Vetiver Systems and by local community action. About 500 acres need to be treated which would involve the planting of about 25,000 yards of vetiver grass hedgerows. The planting material would cost approximately $3 per yard of hedge, a total of $75,000. Cost of planting would under Hawaiian labor rates between $125,000 to $250,000, and much less if done by land owners. At the outside the total cost would be in the order of $325,000. Once planted the hedges would need some maintenance every three years (trimming with industrial weed eater. Easily carried out by the landowners).
What are the benefits: (a) nearly 100% reduction in sediment flow to the sea and consequent improvement of marine ecosystem, (b) prevention of flash flooding and land slippage, (c) reduction in road maintenance cost and other infrastructure damage from storm events, (d) stabilized crop land and improved land productivity, (e) near 100% reduction from farm land of nitrate, phosphate and pesticide pollutants flow into groundwater and streams, (f) improved habitat for wildlife, and (g) an enhanced ecosystem that would allow easier natural establishment of native species.
The total area of 1000 acres would be conserved at a rate of $325 per acre, an insgnificant cost compared to the very high property values in this area.
Elsewhere on O'ahu there are other sediment flows into the sea, all could be prevented in a similar way. For more information see http://picasaweb.google.com/VetiverClients
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Useful gallery of all blog images (with captions) posted on Picassa