Runoff characteristics and application of HEC-HMS for
modelling stormflow hydrograph in an oil palm
catchment
Z. Yusop*, C.H. Chan* and A. Katimon**
*Institute of Environmental and Water Resource Management (IPASA) Univeristi Teknologi Malaysia, Skudai
81310 Johor, Malaysia (E-mail: zulyusop@utm.my)
**Department of Hydraulics and Hydrology, Universiti Teknologi Malaysia, Skudai 81310, Johor, Malaysia
Abstract Rainfall-runoff processes in a small oil palm catchment (8.2 ha) in Johor, Malaysia were examined.
Storm hydrographs show rapid responses to rainfall with a short time to peak. The estimated initial hydrologic
loss for the oil palm catchment is 5mm. Despite the low initial loss, the catchment exhibits a high proportion of
baseflow, approximately 54% of the total runoff. On an event basis, the stormflow response factor and runoff
coefficient ranges from 0.003 to 0.21, and 0.02 to 0.44, respectively. Peakflow and stormflow volume were
moderately correlated with rainfall. The hydrographs were satisfactorily modelled using the Hydrologic
Engineering Centre–Hydrologic Modelling System (HEC-HMS). The efficiency indexes of the calibration and
validation exercises are 0.81 and 0.82, respectively. Based on these preliminary findings, it could be suggested
that an oil palm plantation would be able to serve reasonably well in regulating basic hydrological functions.
Keywords Baseflow; rainfall-runoff modelling; stormflow; storm hydrograph
Introduction
An oil palm (Elaeis guineensis) plantation currently constitutes the second major land use in
Malaysia, covering approximately 4 million ha or about 12% of the country’s total land
mass. The annual export of oil palm products from Malaysia has exceeded USD 8.6 billion
(MPOB, 2005). Due to a lucrative return of this commodity, neighbouring countries,
especially Indonesia, Thailand and Vietnam, are also expanding their palm oil industries. The
establishment of oil palm plantations initially involved the clearing of land, mostly tropical
forests. Replanting to replace less productive old trees is carried out after 25 to 30 years.
Depending on the nature and extent of disturbances, land use activities could have a moderate
to permanent and irreversible impact on the hydrological regimes (Bruijnzeel, 1990).
The population increase and expansion of industrial and commercial sectors have resulted
in greater demands for water. Consequently, the traditional source of clean water from
forested catchments is no longer sufficient to meet the new demand. In this regard, plantation
areas, especially oil palm and rubber, could play a crucial role as the intermediary between
forested landscapes in the upstream and urban or developed ecosystems in the downstream.
If properly managed, plantation catchments can provide substantial runoff with suitable
quality for domestic and non-domestic uses. As such, it is logical to extend more stringent
conservation strategies for water and land resources beyond the forest boundaries.
Despite the importance of plantation ecosystems for socio-economic development and
conservation of water resource, their hydrological role is yet to be fully understood. In the
past, hydrological studies in the tropics were mainly confined to impact forestry activities
(Abdul Rahim and Harding, 1992; Yusop et al.,1998; Yusop et al.,2006). Thus far, the only
report on oil palm hydrology is that of the Sungai Tekam Experimental Catchment in
Pahang, Malaysia (DID, 1989). However, this study only covered the early stage of
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41doi: 10.2166/wst.2007.690

plantation establishment and was terminated before the oil palm reached maturity. The
knowledge gathered from this study is at best inconclusive to support environmentally sus-
tained plantation practice. Therefore, it is timely to have more comprehensive scientific
understanding of the effects of this man-made ecosystem on the environment, particularly
the hydrological regimes. Such information is crucial for the effective and improved manage-
ment of water and other catchment resources. This paper presents the runoff characteristics
and results of hydrograph modelling for an oil palm catchment.
Methods
Study catchment
This study was carried out in a small catchment (8.2 ha) in the upstream of Skudai River
in Johor, Malaysia at 18 43.48
0
N and 1038 32.29
0
E(Figure 1). It is drained by a second
order stream which had been partly straightened during the establishment of the planta-
tion. The catchment’s topography is undulating with an average slope of 7%. The soil
texture is characterised by coarse sandy clay loam of red yellow ultisols and belongs to
Rengam series. Table 1 shows the physiographic conditions of the catchment.
The general climate of the study area is characterised by continuous warm and humid
conditions with annual rainfalls over 12 years ranging from 1,860mm to 2,763mm (average
2,297mm). The mean temperature and relative humidity are 25.6 8C and 87%, respectively.
The monthly rainfall shows two peaks in the months of April and December, suggesting the
influence of south-west and north-east monsoons. With monthly rainfall seldom dropping
below 100mm, the area is not prone to prolonged dry spells (Figure 2). Most of the rainfall
events are of the convective type, characterised by short durations but high intensities.
Figure 1 Location of the study catchment
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