PertanikaJ. Trap. Agric. Sci. 25(2): 149 - 155 (2002) ISSN: 1511-3701© Universiti Putra Malaysia Press

Particle Size Distribution in the Bottom Sediments of the Kemaman RiverEstuarine System, Terengganu, Malaysia

KAMARUZZAMAN, RY., SHAZILI, N.A.M. & MOHD LOKMAN, H.Mangrove Research Unit (MARU),

Institute of Oceanography,Kole} Universiti Sains & Teknologi Malaysia,

21030 Kuala Terengganu, Terengganu,Malaysia

Keywords: Grain size, Kema,man river, monsoon, sedimentation

ABSTRAK

Sedimen permukaan daripada sistem muara Sungai Kemaman dianalisis bentuk butiran saiz bagi memahamidengan jelas proses sedimentasi di muara dan sepanjang Sungai Kemaman. Nilai-nilai statistik tidakmenunjukkan perubahan signifikan mengikut musim tetapi hanya memberi nilai phi (0) yang rendah semasamusim luar monsun berbanding musim monsun. Giri-ciri pernendakan sedimen bagi setiap stesen adalah banyakbergantung kepada gabungan daya fizikal. seperti aliran air tawar, arus pasang surut and ombak.

ABSTRACT

Surface sediment samples from the Kemaman River estuarine system were analysed for the grain size in order tounderstand better the sedimentation processes in the estuary and along the Kemaman river. Their statistical valuesdo not vary significantly according to the seasonal changes but show some relatively lower phi (0) values duringthe non-monsoon season compared to the monsoon season. The characteristics of deposited sediments at eachstation are very dependent upon the combination ofphysical forces such as freshwater runoffs, tidal currents andwaves.

INTRODUCTION

Estuaries and rivers are often regions of highsedimentation, serving as traps for minerals frominland sources transported seaward by rivers,and materials from the coastal ocean transportedlandward. Determinations of the relative contri­butions of inland and marine sources ofsediments in estuaries are necessary for predict­ing and controlling sedimentation in harbours,and becoming the sites of major discharges ofurban and industrial pollutants. Sediment trans­port in estuaries and along the river can beimportant for maintaining navigation channels,dredging harbours, maintaining fish stocks, man­aging water quality and preventing coastal ero­sion. These sediments exhibit a considerabledegree of variability in terms of mineral type,size range and organic content.

It has been well established that estuariestrap particles and some dissolved materials trans-

ported in rivers (Martin et al. 1981; Fox 1981;Kennedy 1984). Consequently, estuarinesediments are considered to be important sinksfor nutrients, organic matter, trace substancesand contaminants derived from inland sources(Simpson et al. 1976; Bopp et al. 1982). In riverineestuaries, as freshwater mixes with seawater,material transport and deposition can be af­fected by river flow, tidal flow, wave activity,currents and non-tidal circulation patterns (Dyer1979). Along submergent coastline estuarine cir­culation is often characterized by a lower salinitysurface layer with a net seaward flow and adenser, more saline bottom layer with a land­ward flow. This upstream or landward flow alongthe bottom causes the estuaries to trap particlesand particle-associated substances from bothriverine and marine sources (Meade 1969;Goldberg et al. 1979). In Malaysia, there is littleresearch done regarding spatial and temporal

KAMARUZZAMAN, B. Y., SHAZILI, N. A. M. & MOHD. LOKMAN, H.

variation of bottom sedimentation along theriver. The information about sedimentation rateor erosion aspects is very limited. Nevertheless,detailed investigation concerning both spatialand temporal variability are required in order tobetter understand the sedimentation processesin the estuaries and along the Kemaman river.

MATERIALS AND METHODS

Description of the Study Area

The study site is located in the Chukai district(04 14.46 N Latitude 103 26.45 E Longitude)which is about 160 km south of KualaTerengganu, the capital state of Terengganu(Fig. 1). In this district flows two major rivers,the Kemaman and Chukai rivers. Although thetwo rivers diverge upstream, they converge down­stream to share a common estuary known as theKemaman estuary. The Kemaman river is thelarger of the two and comparatively has largerdrainage and larger discharge and mean annualoutflow compared to the Chukai river. TheKemaman river has a fresh water discharge ofabout 80 m3/ s during the non-monsoon seasonand 500 m3/ s during the monsoon season. Theirriver catchment areas, rapidly affected by theindustrialization and human activities, has thesea water intrusion limited to a distance of 10km upstream from the mouth. According to theaccumulated data from 1968 to 1987, obtainedfrom the Malaysian Meteorological Service, themonsoon seasons with strong winds and longfrequency periods with mean annual rainfall of3064 mm occurred from November to January.(Fig. 2). Meanwhile the non-monsoon seasonswith low rainfall occurred during April, May andJune.

most landward fresh water point. Since neithertexture nor the grain size of the sediments inthe Kemaman river varied significantly (P>0.05)by the seasonal changes, the data used in thisstudy was the average of both samplings duringthe dry and rainy seasons.

The grain size of the sediments was deter­mined using the standard dry and wet sievingtechniques (Folk 1974). Samples which consistof more than 90% sand were analysed using thedry sieving method, while samples having morethan 90% fme sediments were analysed using~e laser diffraction method. The median grainSIZe of the sediment was estimated by linearinterpolation of the distribution curve. Bothmedian and mean grain size were used in thepreliminary data analysis, although only the meanis presented in this study because both param­eters show equivalent results. Sedimentologicalcharacteristics are reported in phi (0) unitsusing the conversion factor of Folk (1974) asbelow. By using the negative value, coarse grainsize will have a lower phi (0) value which tendsto increase when the particle size becomes finer.

o = -log2 Dwhere D is diameter of particle in mm.

The mean, standard deviation and skewnessof each sample were calculated by the momentsmethod using equations defmed by McBride(1971). The method of moments uses data fromevery grain plot data to obtain statistical infor­mation concerning the sedimentary population.The formula proposed by McBride (1971) usedto calculate the sedimentological characteristicsof mean, skewness and sorting are as follows:

Analytical Methods

Sampling was carried out twice: the first sam­pling during the dry season (May 1993) andthe second during the rainy season Ganuary1993). A total of 14 stations (Table 1) werecollected during both samplings using theekman grab. Out of that, 3 surface sedimentsamples were collected across the mouth of theestuary. Another 11 water samples were col­lected at one km interval inside the Kemamanrivers commencing from the mouth of the riv­ers (Fig. 1). Stations 1, 2 and 3 in the estuaryrepresent the most seaward while Stations 12, 13and 14 along the Kemaman river, represent the

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where;

(1)

(2)

(3)

150 PERTANIKAJ. TRap. AGRIC. SCI. VOL. 25 NO.2, 2002

04° 14.46 N

Fig. 1: Location of study area showing the sampling site along Kemaman River, Terengganu, Malaysia

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Fig. 2: Average of monthly mean rainfall at Kemaman (1981-1994).Data Smtrce: Malaysian Meteorological Service

X0

= mean size00 = sortingSk

0= skewness

f = weight % or volume % (frequency) ofeach class size

n = number of samplem = mid-point of each class size

RESULTS AND DISCUSSION

Sedimentological Characteristic

The sedimentological characteristic of theKemaman estuary, like most other coastal envi­ronments, are very dependent upon the combi­nation of physical forces such as freshwaterrunoffs, tidal currents and waves (Kamaruzzaman1994). However, statistically, neither texture northe grain size of the sediments in the Kemamanriver varied significantly (P>0.05) according tothe seasonal changes (Tables 2 & 3). They onlyshow some relatively lower phi (0) values duringthe non-monsoon season compared to themonsoon season. During the monsoon seasonwhich is associated with heavy rain and highwater current, the water will transport a highconcentration of suspended and fme sedimentsto the estuary areas. Therefore, areas which havestrong currents (Kamaruzzaman 1994) as in Sta-

tions 12, 13 and 14 along the Kemaman riverwould comprise mainly coarser sediments com­pared to the estuary areas which dominantlycomprise fine sands (Tables 2 & 3).

Silt and clay contents of bottom sedimentsin the Kemaman river show a decrease towardsthe estuary. This may indicate that the particletransport in the study area is mainly influencedby river discharge. The bottom sediments forboth the seasons have sand content ranges from42.4% - 100%, silt content from 0% - 32% andclay content from 0% - 23.7% (Table 2). Thedistribution patterns of sand, silt and clay in theestuary (Stations 1, 2 and 3) were dominantlyfme grained sand while the texture in theKemaman river was much coarser grained sand.T~e .percentages of sand were higher (> 80%)Wlthm the freshwater region compared to withinthe estuary. Two probable causes may be for­warded to explain this difference. First, the swiftriver flow allows fine sediment to deposit butthis flow is reduced drastically upon reachingthe larger estuary, thus allowing more fme sedi­ment to be deposited. Secondly, as hypothesizedearlier, the tides also play a significant role intransporting sediments offshore into the estu­ary, thus the offshore materials consisting of

152 PERTANIKAJ. TROP. ACRIC. SCI. VOL. 25 NO.2, 2002

PARTICLE SIZE DISTRIBUTION IN THE SEDIMENTS OF THE KEMAMAN RIVER ESTUARINE SYSTEM

TABLE 1Locations of the study areas along Kemaman River, Terengganu

Station

1234567891011121314

Latitude

04° 14.46 N04° 14.50 N04° 14.58 N04° 14.49 N04° 14.05 N04° 13.38 N04° 13.35 N04° 12.85 N04° 13.25 N04° 12.65 N04° 13.42 N04° 13.25 N04° 13.27 N04° 12.85 N

Longitude

103° 26.45 E103° 26.40 E103° 26.48 E103° 26.15 E103° 25.84 E103° 26.18 E103° 26.25 E103° 25.75 E103° 24.80 E103° 24.65 E103° 24.70 E103° 23.15 E103° 21.00 E103° 20.25 E

TABLE 2Texture and percentage of sand, silt and clay during dry season

Station

1234567891011121314

Sand (%)

88.876.083.144.391.980.085.573.874.696.593.896.298.2100.0

Silt (%)

4.511.76.4

32.03.49.56.35.69.81.53.61.60.00.0

Clay (%)

6.712.310.523.74.710.58.220.615.62.03.62.21.10.0

Texture

Very fine sandModerate sand

Fine sandModerate sand

Fine sandModerate sand

Coarse sandCoarse sandCoarse sandCoarse sand

Very coarse sandVery coarse sandVery coarse sandVery coarse sand

TABLE 3Texture and percentage of sand, silt and clay during rainy season

Station

1234567891011121314

Sand (%)

86.473.879.642.489.378.981.472.670.696.791.195.598.4100.0

Silt (%)

5.512.76.9

34.203.9

10.96.86.810.42.24.11.90.00.0

Clay (%)

8.113.510.513.56.8

10.211.820.622.61.14.82.61.60.0

Texture

Very fine sandModerate sand

Fine sandModerate sand

Fine sandModerate sand

Coarse sandCoarse sandCoarse sandCoarse sand

Very coarse sandVery coarse sandVery coarse sandVery coarse sand

PERTANIKAJ. TRap. AGRIC. SCI. VOL. 25 NO.2, 2002 153

KAMARUZZAMAN, B. Y., SHAZILI, N. A. M. & MOHD. LOKMAN, H.

mostly fme sediments would also be transportedinto the estuary but only little would reachfurther upstream due to the opposing river cur­rents. The lowest percentage of sand was ob­served at Station 4 and this can be explained byits geographical position, which is located closeto the mouth of the estuary and where the 2main rivers meet, providing it with 2 sedimentsources, fluvial and tidal.

Mean (X~)

Mean is an index of grain size measurement dueto its weight. The obtainable mean values candetermine the size of sediment grain. The in­creasing mean value indicates the decreasing ofgrain sizes and vice versa. The mean size gives asimple indication of the magnitude of the force,applied by water or wind which will move thegrains. The mean value along the Kemamanriver ranged from -0.7 to 3.4 0 or ranging fromthe very coarse sand to a very fme sand (Table2). The estuary area (Stations 1, 2 and 3) andsome stations near the estuary (Stations 4, 5 and6) are dominated by the finer sand. Meanwhilethe sampling stations that are far away from theestuary (Stations 7 - 14) are more dominated bythe coarser sandy texture. This can be explainedby the high water velocity from the river inflowwhich may transport the fine sand and leave theheavier sand along Stations 7 to 14. The largeamount of suspended and fme sand will betransported to the estuary, trapped and settledown during a period of slack water or duringtidal.

Standard Deviation (s¢)

Standard deviation is sometimes referred to assorting and indicates the range of forces whichdetermine the sediment size distribution (Briggs1977; Dyer 1985). A large value standard devia­tion (a poor sorting ) indicates that little selec­tion of grain had taken place during transporta­tion deposition. Good sorting, indicated by asmall standard deviation, on the other hand, isproduced by the selective action of energy whichtransports and deposits limited range of grainsize. In this study, sorting does not show asignificance within monsoons and has rangedvalues between 0.7 to 1.6 (Table 4), indicatingthat the sediments in general are moderately topoorly sorted. A moderate sorting was observedat Stations 1, 10 and 11 and these can be ex­plained by their geographical position of theriver with a slope curve which reduces the waterflow and may allow more selection of grain to bedeposited.

Skewness (Sk¢ )

Skewness is the measure of the degree of sym­metry to provide a measure of the tendency ofthe data to spread preferentially to one side ofthe average value. The skewness of each normaldistribution refers to the slope distribution tothe log scale whether symmetrical, positively ornegatively skewed. The symmetrical distributionindicates that the different sizes of sedimentsare similarly distributed. A positive skewness in­dicates an excess of fine grain sizes which couldbe due either to the addition of fme sediment tothe deposits or to the selective removal of the

TABLE 4Average grain size statistical parameters for both sampling in the estuary and along the Kemaman River

Station Mean (0) Standard Deviation (0) Skewness (0) Sorting

1 3.4 0.7 -0.7 Moderately sorted2 1.2 1.1 -0.4 Poorly sorted3 2.2 1.1 -0.5 Poorly sorted4 1.6 1.3 -0.1 Poorly sorted5 2.2 1.5 -0.1 Poorly sorted6 1.2 1.5 1.8 Poorly sorted7 0.1 1.5 1.4 Poorly sorted8 0.7 1.1 0.2 Poorly sorted9 0.5 1.6 0.3 Poorly sorted10 -0.4 0.9 0.3 Moderately sorted11 -0.6 0.9 0.6 Moderately sorted12 -0.7 1.1 1.2 Poorly sorted13 -0.3 1.2 0.8 Poorly sorted14 -0.2 1.1 0.1 Poorly sorted

154 PERTANlKAJ. TROP. AGRIC. SCI. VOL. 25 NO.2, 2002

PARTICLE SIZE DISTRIBUTION IN THE SEDIMENTS OF THE KEMAMAN RIVER ESTUARINE SYSTEM

coarser grain. In this study, as the mean values,skewness in the Kemaman river showed no vari­ation between monsoons (P>0.05) and has awide range from -0.7 to 1.8 which falls from avery positive skew to a very negative skew (Table4). In general, the negative skewness was ob­served at the station near the estuary while thepositive skewness was shown at the station awayfrom the estuary. Station 6 has the highestskewness (1.8) and Station 1 has the lowestskewness (-0.7).

ACKNOWLEDGEMENTThis research was conducted with joint fundingfrom the Malaysian Ministry of Science underthe Intensified Research for Priority Areas (IRPA)project number 51513 and Grant from theMalaysian Toray Foundation (MTSF) projectnumber 63905. The authors wish to expresstheir gratitude to the lab assistants of the Ocea­nography laboratory teams for their invaluableassistance and hospitality throughout the sam­pling period.

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(Received: 23 October 2001)(AcapUd:26June200~

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