SEDIMENTOLOGY OF SEDIMENT BACKSHORE
ALONG THE COASTAL OF ESTUARY JENEBERANG MAKASSAR
Langkoke, R and Budi Rochmanto
burochmanto@yahoo.com
Department of Geology Faculty of Engineering, Hasanuddin University
This paper is presented at Scientific Meeting Collaboration between Department of
Geology and JICA Project for the Development of the Faculty of Engineering
Hasanuddin University, Makassar, August 23rd 2011
Abstract
The research was carried out on the coastal of Jeneberang estuary, to understand
the coastal morphodynamic based on sediment backshore. Location of the
research is along the coastal from Barombong Beach in south to the Tanjung
Bunga Beach the north about 8.5 km length. The research method is drilling at
Barombong Beach, Tanjung Bayang Beach, Tanjung Merdeka Beach, and
Tanjung Bunga Beach about 10 meters – 11 meters depths..The sediment of core
drilling were analyzed sedimentary texture, structures and compositions. Data of
sediment backshore was correlated. Based on the analyzed of core drilling, the
backshore sediment on the study area consist of sands, silts, clays, clay and sand
with organic matter content. Sediment backshore at Barombong Beach shows a
model of marine sediment, while at Tanjung Bayang Beach, Tanjung Medeka
Beach, and Tanjung Bunga Beach show a model of fluviatil delta sediment..
These sediments consist of delta plain sediment, delta front sediment, beach sand
sediment, and foreshore sediment. The Barombong Beach is a stable coast,
however others are unstable coasts.
Key Word: Sedimentology, Sediment Backshore, Estuary Jeneberang Makassar
Introduction
Jeneberang River is one of the biggest river in South Sulawesi. The river flows from
mountainous area of Bawakaraeng Mountain to the Makassar Strait in Makassar. At the
Jeneberang river mouth had formed delta which divided the river to two river mouth, north
river mouth and south river mouth. Between these river mouth, the coastal of Jeneberang
estuary had developed. The Northern river mouth has already closed.
The coastal area included Barombong Beach at the south to the Tanjung Bunga at
north about 8,5 km. length. Estuary Jeneberang coast is very dynamic, naturally and human
activities. At this place accumulation sediment come from fluvial, coastal, and marine
processes,
Backshore is a part if coastal area. This area is always change rapidly, and only
covered by sea water when storm wave happened. This study will be carried out on this part
to understand the coastal morphodynamic based on vertical sediment variation at the
backshore. Hopefully the study will show the history of coastal change and what will be
happened on this area, like the geological concept in modern geology ‘Present is the key to
the Past ‘which is developed to ‘Present Is the key to the Future’.
LOCATION OF THE RESEARCH AREA
The research was carried out in January to April 2010, on the vicinity of the
Jeneberang estuary, around 9 km long, from the Barombong river mouth at the south to the
tip of Tanjung Bunga spit at the north. The area is located at coordinate 5º 08’ 40” S to 5º 12’
40” S and 119º 22’ 40” E to 119º 25’ 20” E in geographic coordinate. (Figure 1)
Research Location
• Geographic Position
5º 08’ 40” S - 5º 12’ 40” S
119º 22’ 40” E - 119º 25’ 20” E
• Length of the coast 8,5 km,
• Barombong Beach at the South to the
Tanjung Bunga Beach at the North
Figure 1 Location of study area.
Aims of the research
The aim of the study is to know the coastal morphodynamic of Jeneberang estuary based on
sediment backshore.
Research Methods
The data were collecting and drillings on the backshore of the Jeneberang estuary coast,
Barombong Beach, Tanjung Bayang Beach, Tanjung Merdeka Beach, and Tanjung Bunga
Beach. The depth of the drilling is 10 to 11 meters. The data, then, were analyzed based on
the sedimentary textures and structures.
Results
The cores drilling were described and analyzed based on sedimentary textures, mineral
composition, and organic matter. Sediment of the cores were clssified based on sedimentary
texture. Generally the sediments show coarsening upward. From the bottom to the top, the
sediments are composed of sand, silt, and clay.
Sand, which is unconsolidated, wet, variation color: brown, brownish black, grey, greyish
black, and greenish grey. The color variation are caused by
mineral composition and
differences on sedimentary environments. Vertically, from the base to the surface, the
sediment shows variation in grain size, and sedimentary structures in the sediments are
alternating between sand and silt, sand and clay, planned bedded, lamination, and lenses. The
organic material found in the sediment are moluscs, and vegetation remains. The variation of
sedimentary textures and structures, and organic matters are used to interpretate sedimentary
environment.
Lanau is characterized by wet, and blackish. Generally it found in the depyh of 11 meters
and 5 meters. This sediments are mainly found in the northern part of Jenebeang river mouth.
Clay is found as intercalated layer in sand. It is characterized by wet, stiky, and contain of
organic remains. Generally clay layer as intercalation in sand wee found in the depth of 11
until the surface.The color of the layers are blackish grey to black.
At some places are found fine sand layers in black color and composed of heavy minerals and
remain of vegetation roots. The remain of vegetation roots indicate the materials were
deposited on the continent. The description of the cores are shown coastal morphodynamic
of Jeneberang estuary.
Discussion
Based on the sediment characteristics, the sediment backshore in the study area can be
classified as swamp sediment, channel sediment, delta plain sediment, delta front sediment,
beach sand sediment, foreshore sediment, and near shore sediment. ( see fig. 2 and 3).
Condition of some those sedimentary environment still exist right now, but the others had
already change because of human activities.

Swamp sediments, consist of clay with various sand content, light brown yo brown,
organic matter content, wet and stiky, intercalation of sand and clay layer abaout 1 to 3
cm. This sediment well develop northward, associated and covered by channel sediment
at Tanjung Bayang, Tanjung Merdeka, and Tanjung Bunga

Channel sediments, composed of sand, grey to black color, grain size from medium sand
to fine sand, At Tanjung Bunga Beach the sediments are coarsening upward in the depth
of 4 to 5 meters. At the depth 7 to 8 meters, the grain size of sediment is fining upward.
Distribution of channel sediment dominantly to northward.(bore hole # 2, 3, 4.)

Delta plain sediments, composed of coarse sand to medium sand with alternating of clay
and silt. The thickness of beds is 10 cm. to 40 cm. Remain mollusc shells are found in this
sediment. This sediment is also characterized by alternating of
coarsening upward
sediment and fining upward sediments. Distribution of delta front sediments found at bore
hole # 2, 3, and 4 with 4 meters to 5 meters thick..

Delta front sediments, is characterized by medium sand to coarse samd and grey to
black in color. The sediment is coarsening upwards with broken shells. The delta front
sediment is found at bore hole # 2, 3, and 4, and the thickness is about 3 meters to 4
meters.

Beach sand sediments, consist of medium sand to fine sand, grey to black in color.
Organic matter content, vegetation roots and broken shells, and planar bedding structure
are also found in the sediment. The sediment is fining upward. This sediments are found
at bore hole # 2, 3, and 4. At bore hole #4, developed swamp sediment. Its indicate
channel sediment had stopped.

Nearshore sediments, consist of fine sand to clay, black to grey in color, organic matter,
humusm and broken shells. At the depth of 11 meter, contain Mollusc fossils Pelecypod
Class ,Spondylus victoriae, Sowerby sp.), dan Julia corbula sentata sp. yang berumur
Pleistocene, and Brachiopod, Prasunata sp, (Pleistocene to Recent). The sediment was
formed at Barombong Beach (bore hole #1).
Conclusions
1. Based on the analyzed of core drilling, the backshore sediment on the study area
consist of sands, silts, clays, clay and sand with organic matter content.
2. .Sediment backshore at Barombong Beach shows a model of sediment marine,
while at Tanjung Bayang Beach, Tanjung Medeka Beach, and Tanjung Bunga
Beach show a model of fluviatil delta sediment.. These sediments consist of delta
plain sediment, delta front sediment, beach sand sediment, and foreshore
sediment.
3. The Barombong Beach is a stable coast, however Tanjung Bayang Beach,
Tanjung Merdeka Beach, and Tanjung Bunga Beach are unstable coasts.
Acknowledgment
The researchers would like to thank to the JICA for supported budget to
conduct the research, and to Department of Geology Unhas for a chance to
present this paper in the scientific meeting.
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