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ABSTRACT
Deforestation activities have been widely known as one of the
devastating factor to the river system and ecological system in a
catchment. Deforestation activities at some areas within the Sungai
Padas catchment has resulted in the changes of land cover
particularly in Tambunan, Sook and Sipitang catchment area. The main
objective of this study is to investigate the direct runoff
hydrograph in Sungai Padas, due to the changes of land cover caused
by deforestation activities using HEC-HMS (version 2.2.2). The
design direct runoff hydrograph resulting from 2, 5, 10, 25, 50 and
100-yr ARI for 72 hours rainfall duration were applied to evaluate
the effect of deforestation on catchment response. The results of
the study indicated that the increase of deforestation approximately
20% has led to the increase of the runoff hydrograph peak and volume
between the ranges of 3.34% to 5.71%, and 3.30% to 5.93%,
respectively, based on 2, 5, 10, 25, 50 and 100-yr ARI for 72-hours
rainfall duration. In addition to the evaluation of runoff
hydrograph due to the land cover changes from forest area into
logged forest area (disturbed forest), the model (HEC-HMS model) has
also been used to evaluate the generation of runoff hydrograph
resulted from the changes of land uses in the future when logged
forest converted into large scale agriculture (e.g. rubber or oil
palm). The result from the study indicated that the cultivation of
large scale agriculture activity causes the additional increase in
runoff hydrograph peak and volume compared to hydrograph resulted
from the logged forest area. The overall results of the study
summarized that the increase of runoff hydrograph peak at Beaufort
discharge station is ranging from 3% to 6% due to 20% increase of
deforestation area without cultivation, and 19% to 30% due to 20% of
the total area converted from deforested area into large scale
agriculture such as palm oil and rubber trees.
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