Sains Malaysiana 39(4)(2010): 525–532
A Numerical Modelling of Seawater
Intrusion into an Oceanic Island Aquifer, Sipadan Island, Malaysia
(Pemodelan
Berangka Kemasukan Air Laut ke dalam Akuifer Pulau Lautan, Pulau Sipadan,
Malaysia)
Mohd
Harun Abdullah & Sarva Mangala Praveena*
Water
Research Unit, School of Science and Technology Universiti Malaysia
Sabah
Locked Bag 2073 88999 Kota Kinabalu, Sabah, Malaysia
Ahmad
Zaharin Aris
Department
of Environmental Sciences
Faculty
of Environmental Studies, Universiti Putra Malaysia
43400 UPM Serdang, Selangor D.E., Malaysia
Diserahkan:
8 Julai 2009 / Diterima: 23 March 2010
ABSTRACT
The primary
source of water on many small islands is the fragile freshwater lens that
floats on saline water in its shallow aquifer. The management of such a limited
groundwater resource on these islands is seriously constrained by the
occurrence of seawater intrusion. Sipadan Island, the renowned and only oceanic
island in Malaysia, had experienced in the over-extraction of its groundwater
for more than ten years to cater for freshwater demand associated with tourism
activities. This paper discusses the output of modelling of seawater intrusion
into the island’s aquifer using SEAWAT-2000. The findings indicated that the island’s coastal aquifer
has been encroached by seawater. The infiltration of isochlor (chloride
concentration) of 2.5 and 45% of seawater and freshwater mixing ratios has
moved 63.4 m and 12.7 m inland from the coastline, respectively. The upconing
event at the pumping well, as simulated by the three-dimensional model, showed
that 14.5% of seawater-freshwater mixing ratio took place below the bottom of
each well. Intensive and unregulated exploitation of groundwater from such an
unconfined aquifer of the island by pumping wells contributed to the upconing.
In order to protect the fresh groundwater resources in the study area from
seawater intrusion, adjustment of groundwater pumping rate is needed. This
study showed that the model is useful in demonstrating the mechanism and
movement of freshwater-seawater interface in the island, and thus provide a
powerful management tool for such an aquifer.
Keywords:
Groundwater; numerical modelling, oceanic island; seawater intrusion
ABSTRAK
Sumber air
primer bagi pulau-pulau kecil adalah lensa air tawar bawah tanah yang terapung
di atas air masin di dalam akuifer. Pengurusan sumber air bawah tanah yang
terhad di pulau-pulau ini dibebani oleh penyerapan air laut. Pulau Sipadan
merupakan pulau yang terkenal dan satu-satunya pulau lautan di Malaysia,
mengalami pengekstrakan air bawah tanah secara berlebihan lebih dari sepuluh
tahun bagi menampung permintaan air bawah tanah yang dikaitkan dengan aktiviti
pelancongan. Makalah ini membincangkan output model kemasukan air laut ke dalam
akuifer pulau menggunakan SEAWAT-2000.
Peresapan isoklor 2.5 dan 45% (kepekatan klorida) nisbah percampuran air laut
dan air tawar, masing-masing adalah 63.4 m dan 12.7 m dari laut ke daratan.
Pembentukan upconing di setiap telaga
pengepaman seperti yang disimulasi oleh model menunjukkan nisbah percampuran
air laut dan air tawar adalah sebanyak 14.5% yang berlaku di bahagian bawah
telaga pengepaman. Pengunaan air bawah tanah secara intensif dan tidak terkawal
dari akuifer pulau ini menyebabkan pembentukan upconing. Usaha untuk
melindungi sumber air bawah tanah di kawasan kajian daripada kemasukan air laut
memerlukan pengubahsuaian kadar pengepaman. Kajian ini menunjukkan model
tersebut adalah berguna dalam menerangkan mekanisme dan pergerakan antara muka
air tawar dan air laut pulau serta sebagai alat pengurusan yang berguna bagi
jenis akuifer seperti ini.
Kata kunci:
Air bawah tanah; kemasukan air laut; model berangka; pulau di lautan
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*Pengarang
untuk surat-menyurat; email: smpraveena@gmail.com
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