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Effect of Vetiver Technology on Sediment Loss and Water Quality in Southern Guam

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Watershed Management to Meet Water Quality Standards and Emerging TMDL (Total Maximum Daily Load) Proceedings of the Third Conference 5-9 March 2005 (Atlanta, Georgia USA) Publication Date 5 March 2005  701P0105.(doi:10.13031/2013.18090)
Authors:   Mohammad H. Golabi, Clancy Iyekar and D. Minton
Keywords:   Vetiver, Sediment loading rate, Water quality, Coral reef

Sedimentation as the result of runoff is the principle anthropogenic threat to environment in general and the water quality in particular in the Pacific Island of Guam. Runoff water is characterized by flash floods of high velocity but short duration. The rapid flow is attributed to low soil infiltration, a high proportion of rain converted to overland flow, and scanty or no vegetation cover due to wildfires. In the areas that protective vegetation cover is at its minimum, the soil is subjected to the high shearing force of such an overland flow.

The on site damage from erosion is indeed a problem to environmental ecosystem of the island. Sediment lost due to erosion clogs rivers, lakes, and waterways. Erosion and sedimentation loss are a major source of water-quality problems in Guam. Sedimentation provides a vehicle for the transport of agricultural chemical residues into the canals, streams, rivers and eventually the near-shore coral reef ecosystems, damaging the coral reefs.

The objective of this project is to make an assessment on the sediment-loading rate to the near-shore coral reef originated from the upland watershed. The effect of Vetiver grass as sediment trapping technique, as well as on water quality leaving the upland watershed is evaluated in this study. To achieve these objectives four plots (72ft X 5.5ft) are laid out on a uniformly sloped (12%) selected watershed to estimate the sedimentation rates. Each plot is equipped with 8-inch high flume wall in order to separate the individual plots surface treatments from each other and surroundings. Flumes are equipped with a cone shape weirs, which will direct the runoff and sediments into a collecting tank beneath the weirs.

In order to evaluate the effect of different soil surface management on erosion and quantify the sedimentation and turbidity of the runoff water from each plot, the following treatments are being examined at this particular watershed:

    a) Natural vegetation As it is treatment
    b) Vetiver technology treatment as a restoration technique
    c) Controlled burned treatment
    d) Exposed surface - No-cover treatment
The above-mentioned treatments represent a wide range of conditions that are present in a typical watershed area in southern Guam.

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