Sains
Malaysiana 38(6)(2009): 851–856
Kemasinan Air Perigi dan Subpermukaan
Lembangan Tuba Langkawi dengan Analisis Hidrokimia dan Survei Keberintangan
Elektrik Menegak
(Well
Water and Subsurface Salinity of Tuba Basin Langkawi by Hydrochemical
Analysis
and Vertical Electrical Resistivity Survey)
Umar Hamzah*, Abdul Rahim Samsudin, Abdul Ghani Rafek & Khairul Azlan Razak
Program Geologi, Pusat
Pengajian Sains Sekitaran & Sumber Alam
Fakulti Sains & Teknologi,
Universiti Kebangsaan Malaysia
43600 UKM Bangi, Selangor D.E., Malaysia
Diserahkan: 31 Julai 2008 / Diterima:
15 Januari 2009
ABSTRAK
Lembangan
Tuba adalah satu endapan aluvium yang terletak di antara perbukitan granit di
bahagian barat Pulau Tuba dan tanah tinggi batuan sedimen Formasi Setul di
bahagian barat. Lembangan ini menganjur timur laut ke arah barat daya sepanjang
hampir 3 km dan mempunyai kelebaran sejauh 2 km. Satu survei geofizik permukaan
menggunakan teknik geoelektrik telah dilakukan untuk mengkaji struktur
subpermukaan dan mengesan kehadiran sebarang akuifer serta jenis nya dalam
lembangan ini. Di samping itu, kepekatan unsur-unsur dalam air tanah juga
dianalisis untuk melihat kebarangkalian berlakunya intrusi air laut ke dalam
akuifer pantai. Sebanyak 22 stesen telah dipilih secara rawak di seluruh
kawasan kajian untuk dilakukan survei geoelektrik duga-dalam. Sementara itu air
bawah tanah telah diambil dari 11 telaga untuk analisis kimia di makmal. Hasil
analisis mendapati semua sampel air perigi ini adalah berjenis air tawar.
Profil keberintangan pada arah timur laut - barat daya yang menganjur dari Teluk
Berembang hingga Teluk Bujur mempunyai nilai keberintangan yang berkisar di
antara 4 Ωm sehingga infiniti. Lapisan
teratas yang mempunyai ketebalan sekitar 1-3 meter dan berkeberintangan 4 -12 Ωm
ditafsirkan sebagai lempung manakala lapisan di bawahnya yang berketebalan 10
hingga 50 meter dengan nilai keberintangan 2 - 480 Ωm ditafsirkan
sebagai bahan berpasir dengan air tawar atau pasir berair payau. Keberintangan
berjulat ribuan ohm.m hingga infiniti dianggap mewakili batuan dasar granit dan
batu kapur. Kedalaman maksimum yang dicapai oleh survei keberintangan ialah
sekitar 70 m.
Kata kunci:
Analisis kimia; akuifer, air masin; keberintangan elektrik; survei geoelektrik
ABSTRACT
Tuba basin
is an alluvial deposit located between granitic hill in the western part of
Tuba Island and the Setul formation sedimentary rocks in the eastern site of
the island. This basin stretched along 3 km in the NE-SW direction with an estimated width of about 2 km. A geophysical
survey using geoelectrical technique was carried out to figure out the
subsurface structure, to detect the presence of underground aquifers and to
investigate any saltwater intrusion into these aquifers in the basin.
Concentrations of several elements in the well water were also analyzed to
investigate any occurrence of salt water intrusion into the coastal aquifers.
For this purpose, the vertical electrical sounding surveys were carried out at 22
randomly distributed stations in the study area. Water samples were also taken
from 11 wells for hydrochemical analysis in the laboratory. Our results showed
that all water samples were of fresh water type. Electrical resistivity profile
constructed from stations located in NE-SW direction from Teluk Berembang to Telok Bujur shows a wide range
of resistivities ranging from 4 Ωm
to infinity. The top layer with a thickness of 1-3 m and resistivity values of
4 – 12 Ωm is interpreted as clay zone. This layer is overlying a
much thicker layer of 10-50 m with resistivity values of 2 - 280 Ωm
representing sandy material that may contain fresh water or sand with brackish
water. Layers with resistivity values from thousands ohm.m to infinity are
interpreted as either granite or limestone bedrock. Maximum thickness observed
in this resistivity survey is approximately 70 m.
Keywords:
Aquifer; chemical analysis; geoelectrical survey; resistivity; saline water
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*Pengarang untuk surat-menyurat;
email: umar@ukm.my
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