THE EFFECT OF TYPES OF VEGETATION ON SLOPE ALONG THE NORTH-SOUTH EXPRESSWAY

North-South Expressway is an infrastructure network constructed to link North area and
South area in Peninsular Malaysia. The expressway involves of many cut-off slopes
during its construction. The disturbance slope will change its stability that lead to slope
failure such as erosion and landslide. The main objective of this study is to investigate,
determine and analyze the effect of types of vegetation on slopes along the North-South
Expressway. Eight selected slopes are chosen as study site. The study involves some
methodologies. Research, data collection of slope data, rainfall data and vegetation data,
data analysis using USLE method, distribution particle size test to determine soil types
become very helpful methods in verifying results to meet the goals of project. The result
from the USLE calculation shows tree or woody vegetation provides greater mechanical
reinforcement and buttressing action because it has stronger and deeper rooted, so it is
best for slope protecting, compared to fern and bushes that protect only surficial slope.
Slopes with tree give the lowest value of soil loss in the range of 95.54 to 162.23 tons
for all years, followed by slopes with bushes by 17134.92 to 60153.61 tons. Slopes with
fern give the highest amount of soil loss with 24552.69 to 95059.04 tons. Hence, bushes
give better protection towards soil erosion compared to fern. Thus, tree is the type of
vegetation that works best in protecting soil erosion, followed by bushes and fern. Error
in this estimation can occur because the USLE is an empirical equation that does not
mathematically represent the physical processes of soil erosion. However, the relative
results from different years may still be useful to predict the trend of soil erosion.