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ABSTRACT |
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TITLE: |
The Use of Vetiver Grass System for Erosion Control and Slope Stabilization along the Yadana Gas Pipeline Right-of-Way |
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AUTHOR(S): |
Dr. Songkiert Tansamrit - 240299@ptt.or.th
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The 238.5-kilometer Yadana
Gas Pipeline of the Petroleum Authority of Thailand (PTT) passed a
50-kilometer strip of forest in which 20-meter width was allowed for use
during construction, amounting to around 600 rai of
area. Bare soil results from the construction was
immediately exposed to erosion. Without any preventive measure, especially
for the Slope Complex Soil Series in high mountain area, erosion rate may
increase by 100 times. To minimize environmental impact during
construction and to achieve maximum effectiveness in rehabilitation,
construction strategy was formulated to create permanent soil erosion control
structure with physical erosion design approach, i.e., soft plugs,
diversion berms and drainage system, combined with re-vegetation and
agronomic erosion control methodology along the pipeline right-of-way. Vetiver grass was specifically introduced in high-risked
erosion areas. Erosion Rating was calculated and
classified into low risk (E0), moderate risk (E1), high risk (E2) and very high
risk (E3) with the following details: E1 Areas: Building permanent soil
erosion control structure, re-vegetating with 3 kinds of leguminous covers,
sowing of various grass species and immediate re-vegetation before the first
rainy season, and E2 and E3 Areas: Building permanent soil erosion control
structure including soft plugs and berms as well as vetiver
grass planting, sowing of various grass and leguminous species before the
first rainy season and re-vegetation before the second one. Vetiver grass was planted in the E2 and E3 Areas along the
contour line, 10-15 centimeters apart, along the same contour furrow while
hedgerows were spaced about 1-1.5 meters, amounting to 1.5 million slips used
in this project. In the E3 Area with over 35 degree slopes,
berm construction may not prevent erosion during the first rainy season;
therefore, jute sacks filled with a mixture of soil and grass seeds were
arranged in ladder-pattern, pegged with live stakes. Grass and legume seeds
were sowed. Sacks were holed and planted with vetiver
slips so that their roots grew into the soil while sacks naturally decayed.
Those laddered jute sacks naturally formed permanent soil ladders covered
with vetiver grass and other grasses. Vetiver grass indeed plays a very significant part in
making physical erosion control structure a naturally permanent erosion
structure. |
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