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Sains Ma1aysiana 25(3): 77-90 (1996) Sains Bumi/ Earth Sciences
Sungai dan Pantai Kuno di Kompleks Delta Kelantan (Old River and Beach at the Kelantan delta complex)
Kamal Roslan Mohamed & Che Aziz Ali Jabatan Geologi Universiti Kebangsaan Malaysia 43600 UKM Bangi Selangor D.E.
ABSTRAK
Kajian ini dilakukan berdasarkan imej LANDSAT TM tahun 1989, dan dibantu oleh peta topografi serta gambar udara. Beberapa peringkat pembentukan dan perkembangan Delta Kelantan ditafsirkan daripada bentuk dan kedudukan alur-alur dan permatang pantai kuno. Delta lebih tua berbentuk juring ("cuspate") dan beting-beting pasir di bahagian selatannya menandakan arah garis pantai terdahulu. Delta yang lebih tua ini lebih mencirikan delta kuasaan ombak, berbeza dengan delta yang sedang terbentuk sekarang. Perubahan daripada delta kuasaan ombak kepada delta kuasaan sungai terjadi akibat perubahan-perubahan di bahagian daratan dan pesisir pantai. Di bahagian daratan, imej LANDSAT TM menunjukkan Sungai Kelantan telah menukar arah aliran beberapa kali dan ini mengakibatkan perubahan kedudukan muara. Imej yang diperolehi juga menunjukkan terdapat banyak alur-alur sungai tua yang luas tetapi mempunyai aliran yang kecil, ataupun alur-alur yang kering. Selain itu terdapat juga beberapa tasik memanjang dan tasik ladam, hasil tinggalan sungai lampau. Daripada bentuk dan kedudukan alur-alur sungai tua ini, dapat ditafsirkan sungai utama telah berubah berbentuk dari berliku menjadi lurus beberapa kali. Di bahagian pantai pula telah dikesan garis pantai telah berkembang secara progressif ke arah laut (progradasi). Perkembangan garis pantai ditandai oleh permatang pantai yang berkedudukan hampir selari dengan garis pantai sekarang. Permatang pasir ini boleh dikesan hingga 10 km daripada garis pantai sekarang. Pada peringkat awal pembentukan Delta Kelantan, bukit Gunung Panchor (pekan Gunung) dan Bukit Marak merupakan sebuah pulau atau bukit di pesisir pantai sementara kedudukan bandar Kota Bharu masih terletak di laut. Pada masa yang sama muara sungai berhijrah secara berperingkat-peringkat ke arah baratlaut. Muara terawal yang dapat dikesan merupakan muara Sungai Kemasin dan kemudian menghijrah ke muara Pengkalan Datu. Sebelum berubah kepada kedudukan sekarang, muara Sungai Kelantan telah berhijrah daripada Pengkalan Datu ke Kuala Pak Amat. Perubahan kedudukan muara menyebabkan tindakan proses fizikal (rambatan ombak, angin dan arus pantai) berbeza daripada sebelumnya. Pada masa ini sebahagian besar daripada bahagian luar kompleks delta dipengaruhi oleh aliran pesisir pantai yang menghasilkan pembentukan anak tanjung pasir (sand spit) di bahagian pinggir delta. Kehadiran anak tanjung pasir secara langsung melindung kompleks delta daripada tindakan ombak dan menyebabkan pengaruh luahan sungai dan pasang surut lebih dominan di bahagian dalam kompleks.
ABSTRACT
This study is based on a LANDSAT imagery of 1989, topographic maps and aerial photographs. Several stages of the delta's development have been identified based on the shape and the position of the former delta lobes and channels. The older delta complex shows a cuspate shape and a series of beach ridges in the south marks the position of the former shore lines. There is a clear distinction between the former delta complex and the present day complex. The former lobe shows a characteristic of a wave dominated delta system whilst the present complex is more of a fluvival-dominated type. The change in the delta type is believed to have been caused by the change of physiographic processes in the delta area as well as in the inland area. In the inland area, the Kelantan River has changed its course several times that were followed by delta-lobe switching. At the same time the river mouths migrate progressively towards the northwest. The Kemasin River mouth is the oldest river mouth detected from satellite's imagery and aerial photographs. The rivermouth then migrated to the north and forms the present day Kuala Pak Amat before it migrated further northwest to Pengkalan Datu. The migration of river mouth has led to the change of the deltaic processes. Earlier when the river mouth and the delta complex were located in the south they were subjected to direct wave action. At present most of the delta complex is subjected to the northwesterly longshore currents which have produced a series of sand spits. The presence of the sandspits which are sheltering the river mouth from wave action has led to more current and stream domination on the delta. Some older river channels which form dried up channels and dying streams can be clearly observed in the satellite imagery. There are also some remnant river channels which form elongated lakes and ox-bow lakes. Shapes and locations of the older river systems reveal that the main stream has changed its behavior from a meandering stream to a straight channel river system several times in its history. In the coastal areas, we have traced several older shorelines which had prograded progressively towards the sea. The progradation of shorelines is marked by a series of beach ridges which are parallel to the present day shoreline. The beach ridge can be traced up to 10 km inland from the present day beach line. Several topographic highs (Gunung Panchor and Bukit Marak) are believed to represent small hills or near shore islands during the beginning of the progradation.
RUJUKAN/REFERENCES
Boggs, S. 1987. Principles of Sedimentology and Stratigraphy. Galloway, W. E. 1975. Process Framework for describing the morfologic and stratigraphic evolution of deltaic depositional system. Deltas, Models for Exploration, Suntingan M. L. Broussard. Galloway, W. E. & Hobday, D. K. 1983. Terrigenous Clastic Depositional System. Springer-Verl Kamal Roslan Mohamed & Che Aziz Ali 1995. Delta Kelantan: Perubahan geomorfologi berasaskan tafsiran imej LANDSAT TM. Newsletter of the Geological Society of Malaysia 21(3): 200-201. Koopmans, B. N. 1972. Sedimentation in the Kelantan Delta (Malaysia). Sedimentary Geology 7: 65-84. Reading, H. G. 1986. Sedimentary Environments and Facies. Second edition. Selley, R. C. 1988. Applied Sedimentology. Academic Press.
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