1. water depths and bottom profiles of the mahakam river around

Iwan Suyatna : Water Depths and Bottom Profiles of fhe Mahakam River Around Samarinda Downtown

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Natural Life, Vol. 2. No.1, 2007, 1-11, ISSN: 1829-653X Research Institute of Mulawarman University, Samarinda, Indonesia

WATER DEPTHS AND BOTTOM PROFILES OF THE MAHAKAM RIVER AROUND SAMARINDA DOWNTOWN

Iwan Suyatna

Faculty of Fisheries and Marine Science, University of Mulawarman Jln. Muara Pahu, Kampus Gunung Kelua, Samarinda 75119, Indonesia

Abstract

Mahakam river plays an important role for the people of Samarinda and East Kali-mantan such as for transportation; raw material of drinking water and other daily eco-nomic activities. Physically, nowadays water condition of the river is much different compared to previous time especially the color of water and the sedimentation rate. These two environmental factors may affect water depth of the river.

Related to the problem and to get an idea how deep the river of Mahakam at present day, water depths at certain location around Samarinda downtown were surveyed. Survey was carried out at 5 stations : 1) Ship port area of the hinterland/gas station Loa Bakung, in December 2006; 2) Ship port of the United Tractor Loa Bakung, in November 2006; 3) The Muara Karang Asam area, June 2006; 4) The Selili area, June 2006; 5) In The Bridge of Mahkota Dua in December 2005; and 6). In the Bridge of Mahakam, in December 2005.

Water depths survey was started from the edge across the river at each station by using the Echo sounder of MARK II. The device was installed inside a small motorized wooden boat; the geographycal position of the start and end point of survey at each the station were made by GPS Garmin 60csx.

The survey found that the deepest water depth of the Mahakam river around Sama-rinda downtown was found at the bridge of Mahakam, 33.0 m; followed by the bridge of Mahkota Dua, 32.0 m and the Ship port of hinterland/gas station Loa Bakung, 29.0 m; while others namely Muara Karang Asam, Selili and Ship port of United Tractor Loa Ba-kung were 23.0 m; 17.0 m and 12.0 m respectively.

The result shows that upstream area had smooth bottom profile if compared to steep bottom profile at downstream area.

Key words : water depth, bottom profile, Mahakam river, Samarinda 1. Introduction

A. Background

Mahakam river has long more than 600 km. The river cuts a cross the provin-cial capital of Samarinda and it is affected by sea and therefore waters of Mahakam

undergoes up and down twice daily as Makassar strait has type of diurnal tide.

It is so far clearly understood that Mahakam river plays important roles on many purposes mainly for transportation as inhabitants of East Kalimantan are dis-tributed along the Mahakam river sides till


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to the hinterland and this makes river is crucial transport system in these areas. Other functions are such as for raw ma-terial of drinking and tap water, source of food (fish, shrimp and clamp) and recreation as well. According to Dutrieux (2001) the drainage basin of Mahakam river covers about 75,000 km2. Nowa-days, mainly due to human disturbance which has been taking place since long time a go, such as extensive land clearing within the mountains, logging, agricultural activities and settlements purposes have accelerated the erosion. According to Al-len et al. (1979) in Dutriex (2001) Maha-kam river has a high discharge rate of

1500 m2/s; while Tomascik et al (1997) state that Mahakam river has an annual runoff of about 1.5 x 103 m3 sec-1. As a result, upstream activities as mentioned above and around Samarinda itself for city evolution purposes cause increasing sedi-ment load into Mahakam river and affect not only on the water color but also the water depth and therefore ship ports of several companies around the city now become more frequently to do a dredge.

In relation to this, several surveys of water depth around Samarinda downtown had been carried out to dekamine water depths since the actual data in general are very rarely.

B. Objective

In the frame of sedimentation prob-lem and the issues of Mahakam river as explained earlier, one important thing that-should be carried out is surveying the wa-ter depth of Mahakam river. The survey

aimed to know the actual water depths as well as the bottom profiles of the river at certain location and then the result of the survey may describes us concerning the present condition of Mahakam river.

2. Materials and Methods

Survey was conducted in Decemcer 2005; June, November and December 2006. It was conducted around Samarinda downtown at in the following locations these are 1). Ship port of Pertamina Ka-rang Asam; 2). Ship port of the United Tractor Loa Bakung; 3). Muara Karang Asam; 4). Selili; 5). Bridge of Mahkota Dua; and 6). bridge of Mahakam.

Water depth survey was started from the edge acrossed the river at each station that was started from North Side (Start Point) to South Side (End Point), see Fig-ure 1. The start and end point were consi-dered as a transect of survey. Earth/geographycal position of start point and end point of each station was made by GPS Garmin 60cs. Survey of water depth

was done straight from start point to end point.

The survey was using the Echo sounder of MARK II. The device was in-stalled inside a motorized wooden boat (boat dimension : 10.0 m length; 3.0 m width and 1.50 m height). During survey, the device displayed water depths and bot-tom profiles as well on its monitor. The two parameters were printed-out on ther-mal paper (echogram) as thick black line. The black line was then measured by using ruler to obtain its length in cm (B). While to get an idea of survey distance for each station in field, it was obtained by convert-ing two earth/geographycal positions (start and end point) into distance unit in meter (A). On the same paper, vertical lines having scale number were also presented to show water depth in meter. Ratio be-


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tween length of station surveyed (A) and length of the thick black line (bottom pro-file) on the paper (B) or A\B is a scale and appeared on the graph of the bottom pro-files. To show the location and the sta-tions of the surveys on a map, a Geograph-ic Information System MapInfo version 8 was used. 3. Results and Discussion

The following table shows location and stations of the water depth surveys. The stations were selected randomly, it means no specific aims, just to know the depth from edge across the river and the

configuration of bottom profiles for each station surveyed. To give an idea how the survey moves from Start Point to End Point, see Figure 1. It is also showing where the stations were located around Samarinda downtown.

Water depth of all the stations were surveyed straight from Start point to End point except at the station 4, Selili (Front of the river mouth of Karang Mumus), it was at the time of the survey the water current was very strong and causing the survey boat to drift and therefore the boat had to face the current, see Figure 1.

Table 1. Stations, geographycal positions and length transect observed during the water depths Mahakam river survey.

Geographycal position Length transect No. Station Start point End point observed

(in meter) 1 Ship port of S 0o 32’ 00,60” S 0o 32’ 22,30” 685.0 United Tractor E 117o 05’ 56.10” E 117o 05’ 56.20”

2 Ship port of hinter- S 0o 31’ 47.90” S 0o 32’ 03,50” 652.0 land/Gas station E 117o 06’ 45.90” E 117o 07’ 00.00” of Sungai Kunjang

3 Bridge of Mahakam S 0o 31’ 12.00” S 0o 31’ 18.30” 349.0 E 117o 07’ 20.93” E 117o 12’ 18.20”

4 Muara Karang S 0o 30’ 03.85” S 0o 30’ 29,91” 840.0 Asam E 117o 07’ 38.49” E 117o 07’ 44.51”

5 Selili (Front of river S 0o 30’ 29.74” S 0o 30’ 36,64” 1,007.0 Mouth Karang Mumus) E 117o 09’ 24.66” E 117o 08’ 54.71” S 0o 30’ 34.48” E 117o 09’ 21.67”

6 Bridge of Mahkota Dua S 0o 30’ 03.85” S 0o 30’ 29,91” 221.0 E 117o 07’ 38.49” E 117o 07’ 44.51”

Source : Primary data, 2005-2006.


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Figure 1. Location and stations of water depths Mahakam river survey

around Samarinda downtown.

Only the station 1, port of United Tractor Loa Bakung that had smooth bot-tom profile, while others were steep. This condition could be the result of the veloci-ty of water current throughout the water column which weak and almost the same; no extreme strong water current; the se-dimentation was occurred all over the bot-tom and therefore its water depth along the transect did not appear different. The wa-ter depth ranged from 6.0 to 12.0 m (Fig. 2); while others, Fig. 3 to 7 ranged from

6.0 to 29.0 m (station 2) ; 6.0 to 33.0 m (station 3); 1.5 to 23 m (station 4); 3.0 to 17.0 m (station 5) and 9.0 to 32.0 m (sta-tion 5).

Unlike the station 1, the bottom pro-files of station 2 to 7 (Fig. 2-7) were steep as explained above. This may tell us that water current at all the stations mentioned were strong enough at certain part of the water coulumn and affected the riverine bottom to erode and finally river becomes deep perhaps very deep (Fig. 3 to 7).


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Figure 2. Water depths and bottom profile at the station of ship port of United

Tractor, Loa Bakung Samarinda (Scale 1 : 4280).

Figure 3. Water depths and bottom profile at the station of ship port of hinterland/ Gas Station, Loa Bakung Samarinda (Scale 1 : 4345).

At the station 3 (Fig. 4), in the bridge

of Mahakam the extreme depth area was wider than the shallow area, this indicates that almost whole column of body of wa-ters flows strongly. While others are on contrary, where the shallower area was

wider than the deeper depth, mainly for the station 2, Ship port of United Tractor Loa Bakung; station 4, Selili (Front of the river mouth of Karang Mumus and 5, Bridge of Mahkota Dua.

WAT

ER

Bottom Profile

Bottom Profile

WAT

ER


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Figure 4. Water depths and bottom profile at the station of bridge of Mahakam,

Samarinda (Scale 1 : 2180).

Figure 5. Water depths and bottom profile at the station of Muara Karang Asam,

Samarinda (Scale 1 : 5250).

Geomorphologically, station 2 up to 6 seemed naturally to be able to alter water current velocity to flow become more rap-id. This perhaps related to the topography

of the Mahakam river; more drop the bot-tom more rapid`and stronger the water current to flow.

Bottom Profile

Bottom ProfileW

ATER

W

ATER


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Figure 6. Water depths and bottom profile at the station of Selili (Front of river mouth of Karang Mumus), Samarinda (Scale 1 : 6710).

Figure 7. Water depths and bottom profile at the station of bridge of Mahkota Dua, Samarinda (Scale 1 : 1380). Of 6 figures, 1 figure (Fig. 5) shows

that edge part of the station 4, Muara Ka-rang Asam, was most shallower compared with others, the deep was not more than 1.5 m and the shallow depth extends up to more than 100.0 m away from the edge. Visually the reason is that at the place the water current was circulating with weak

velocity but the other side, the deep area, the current water was strong (Fig. 8).

Bottom Profile

Bottom ProfileW

ATER

W

ATER


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Figure 7.1. A view showing the sedimentation at the station 4, Muara Karang Asam, a place where a water current circulation was taken place.

The returned water current was com-ing from the main water current that was blocked by the riverine wall ahead and then the wall returned back part of the wa-ter currents and flowed along the edge of river, but the velocity became slower, fi-nally this condition influenced suspended sediment to sink to the bottom, so far much sediment in waters of Mahakam river is predictable resulted from the eroded upstream area .

The decreasing water depth here surely has been taking place since years ago. Bates and Jackson (1980) in Tomas-cik et al (1997) stated that sedimentation can be defined as the act or process of de-positing sediment by mechanical means from a state suspension in water, or as a

process of forming and accumulating se-diment in layers. The sedimetation rate of suspended particulate matter (SPM) ac-cording to Tomascik et al (1997), depends firstly on the physical structure of the par-ticles themselves i.e. density, and finally on the hydrology of the area i.e. current velocities, shear stress, vertical location of SPM in the water column, settling veloci-ties of particles and turbulent mixing. Re-fering to the problem, perhaps biosphere reserves are very urgent and needed to im-plement. Quali and Fazi (2001) say that Biosphere reserves are areas of terrestrial or coastal ecosystem that are inter-nationally recognized for promoting and demonstrating a balanced relationship be-tween people and nature.


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Figure 8. Major sedimentation zone (in circle) around location surveyed in Samarinda.

Previous survey done by Suyatna (2006) showed that at every curve of river, the water current tends to flow stronger and may erode the bottom and the wall of river as well, and therefore at this location water depth at certain part is extremely more deeper (steep) and the river width is wider except for the bottom and the wall are composed by the hard substrate such as rock.

At the station 3, bridge of Mahakam, and station 6, Mahkota Dua, their widths are more narrow compared

with others, ranging between 349.0 and 221.0 m respectively,the reason could be because of both of their wall at the south-ern side (Samarinda Seberang side) is the rock crag associated with plants (Fig. 9), but the bottom could be soft substrate and as always swept by the water current caus-ing the water depth much more deeper.or naturally it was already formed before as the original topography of Mahakam river.


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Figure 9. The rock crag associated with terrestrial plants of the river wall at the station 3,

bridge of Mahakam and the heap at the view is the End Point of the water depth survey of the station (photo : Iwan SUYATNA, 2006).

4. Conclusions

Water depths and bottom profiles survey that were carried out around Sama-rinda downtown found the following con-clusions : 1). The deepest water depth and the most

steep bottom profile were found at the station 3, bridge of Mahakam. Howev-er it seems similar with the station 6, bridge of Mahkota Dua. Other stations such as station 2, Port hinterland/Gas station Loa Bakung; 4, Muara Karang Asam; and 5, Selili (Front of the river mouth Karang Mumus) were also hav-

ing steep bottom profile but the water depth was shallower. These stations may could be grouped as the down-stream area.

2). The most shallow of the water depth and the most smooth of the bottom pro-file were found at the station 1, Port of United Tractor. This may could be grouped as upstream area.

3). Upstream area had smooth bottom pro-file compared to downstream area steep bottom profile.

REFERENCES

Dutrieux, E. 2001. The Mahakam Delta Environment, From the 80’s up to now : A Synthesis of a 15-year Inves-tigation. Les Athamantcs, 740 Av. des Aphoticaircs, 34090 Montpellier, France. Optimizing Development

and Environmental Issues at Coastal area : Problem and Solution for Sus-tainable of Mahakam Delta. Proceed-ing of International Workshop. Edi-tors Tridoyo K, Dietriech G. B. Bam-bang W and Imam S. P. 63-68.


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Quali, H and Stefano, F. 2001. Conser-vation and Sustainable Management of Coastal Ecosystem. A summary on UNESCO’s Activities in Southeast Asia. Optimizing Development and Environmental Issues at Coastal area : Problem and Solution for Sustaina-ble of Mahakam Delta. Proceeding of International Workshop. Editors Tri-doyo Kusumastanto; Dietriech G. Ben-gen; Bambang Widigdo and Imam Soeseno. P. 93-102

Suyatna, I. 2006. Profil Kedalaman Sun-gai Mahakam di Sekitar Kota Sama-rinda. Lembuswana. Media Peneliti-Sejarawan-Budayawan. Vol. VI no. 58. Januari 2006. P. 1-7.

Tomascik, T; Anmarie J, M. Anugerah,

N and Mohammad K, M. 1997. The Ecology of the Indonesia Seas. Part I, Chapter 1-12. Vol. VIII. Pe-riplus Edition. 642 p.

1. water depths and bottom profiles of the mahakam river around

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