Grain size analysis report on Karnaphuli river bank sediments. Md. Yousuf Gazi

1. “Grain size analysis report on Karnaphuli river
bank sediments”
Md. Yousuf Gazi
Department of Geology
University of Dhaka
1st
year student

2. Geological Background:
Sitapahar structure It lies east of the Patiya and the west of the Gilasari and the Belasari
structures. On the north of the Sitapahar anticline, Changotaung anticline is situated while
bandarban anticline is located on the south. The Sitapahar anticline is a N20°W-S20°E trending
structure plunging 6° in S18°E. The structure is about 40 km in length. Its steeper western flank
is overturned in some places.The Karnafuli river is the main channel of the drainage system in
the area. The courses of most of the important tributaries are parallel to the main range trending
NNW-SSE and appear to be controlled by structural trend of the area. One of the most
significant geomorphological features of the area is the course of SILCHHARI stream along the
anticlinal axis. The stream is following the anticlinal valley and this type of valley is developed
if comparatively weaker rocks are exposed along the axis. [Sifatul Quader Chowdhury].
A considerable thickness of clastic sediments of Miocene age is exposed on the western flank of
Sitapahar Hill Range at Kaptai under the district of Rangamati in Bangladesh. So Kaptai is one
of the most important places from the geological point of view. A comprehensive study was
undertaken in that area in multidiscipline of geology within a short span of time. Hence, this
article includes the gist of the overall geology of Kaptai region; particularly of Sitapahar
anticline, where multidisciplinary approaches like geomorphology, stratigraphy, structural
geology, and to some extent tectonic behavior of that area are incorporated.
The tectonic evolution of this region ranges from Cretaceous through Tertiary to Quaternary.
The study area comprises a continuous succession of sandstone, silt stone, and shale. The rock
sections are divided into three lithostratigraphic units, mainly on the basis of gross lithology.
These units are equivalent to upper Bhuban, Bokabil, and Alluvium Formations.
Due to the absence of paleontological records in the area, actual age determination of the rocks
was not possible. However, from correlation, it is found that the rocks are of Miocene age.
Sandstone, silt stone, and shale of this area are being used for different purposes, which have got
economic importance to some extent. The region is supposed to contain oil and gas as some of
their traces were found. Hence detail exploration should be accomplished immediately.

3. Population:
The total population is 5,08,182 according to 2005 census of which tribal 52% and non-tribal
48%. The number of males is 2,87,060 and the females are 2,38,043 (Census 2001). The density
of population is 83 per square kilometer (Census 2001). The number of household is 1,03,974
having the household size 4.8 (Census 2001). The total population is divided into Bangalees and
eleven tribes (ethnic minorities):Chakma, Marma, Tanchangya, Tripura, Pankua, Lushai, Khiang,
Murang, Rakhain, Chak, Bowm,Khumi.
Tribal population : (as per census of 2005 ): Chakma-1,86,395, Marma-44,727, Tanchanga-
18,607, Tripura-6,697, Pankho- 2,118, Bowm-1,053, khyang- 791, Lusai- 217, Chak- 177,
Rakhain-70, Khumi- 50, Gurkha-03, Etc.-174.
As per 1991 census, the religious breakup of the population of the district were: Buddhist
53.83%,Muslim 39.28%, Hindu 5.62% and Christian 1.12%. Religious institutions Pagoda 1230,
Mosque 1059, Temple 65, Church 16. Genderwise, male constituted 53.59% and female
constituted 46.41% of the population.

4. Geography:
Rangamati is located in the Chittagong Division. It is bordered by the Tripura state of India to
the north, Bandarban District to the south,Mizoram State of India and Chin State of Myanmar to
the east, and Khagrachari and Chittagong Districts to the west. The area of the district is
6116 km2
of which 1292 km2
is riverine and 4825 km2
is under forest vegetation.
Climate:
It is highly difficult, if not impossible, to forecast what the weather will be like at a certain time
in a very precise place. And yet, all travellers would like to know in advance the climate
conditions in order to organize their future trip. Average temperatures or rainfall can help you to
get a good idea of the issue. The temperatures mentioned hereafter are expressed in degrees
Celsius and represent the monthly averages observed over a great number of years.

5. Drainage and Streams
The Karnafuli The principal river of the region. It originates in the Lushai Hills of Mizoram
(India), flows through Rangamati and the port city of Chittagong and discharges into the Bay of
Bengal near Patenga. A number of STREAMS flow upstream of Rangamati. The streams are: one
originating near Thekamukh in Mizoram-Bangladesh border flowing through
Harina, BARKAL and Sublong; one originating at Marishwa through Myanmukh and Langadu till
reaching Subhalong; one flowing through Dangumura to Myanmukh; and one flowing through
Mahalchhari to Rangamati. The streams meet near Rangamati and their combined flow is known
as Karnafuli. The river is flashy and its length is about 131 km. Rainkhiang, Sublong, Thega,
Kasalong, Ichamati and Halda are its main tributaries. Its major distributaries are Saylok' and
Boalkhali.
The only hydropower station of the country was built by constructing a DAM on this river
at KAPTAI. The Karnafuli is navigable at Barkal and Kaptai but above Barkal it is shallow. With
the construction of the Kaptai dam, this river has been blocked, and a large artificial lake has
been created, and the bed of the river has also been much widened. This man-made lake provides
a network of all-weather navigable routes in the area. Downstream of the dam the Karnafuli
receives very little water in the dry season. The opening of the sluice gates of the dam creates
water movement from the lake downstream. The river finally discharges into the Bay of Bengal.
The port city of Chittagong is situated at the mouth of the river. BANGLADESH WATER
DEVELOPMENT BOARD (BWDB) collects water level data through its 3 hydrometric stations
located at Kodala, Chittagong and Patenga.

6. Culture:
The area is sparsely populated and presents and interesting disparity with thegeneral
demographic picture in Rangamati. The people live on the top of the hillsand also on foot of the
hills. The life is very hard in the investigated area as themajor part of the population of the
area live mostly along the foot hills and most ofthe tribal people live on the hilly region.Total
population of the Rangamati district is about 400000. Population density isabout 6000 per sq.
km. Most of the people are poor and maintain their lives byhandicrafts and also cutting woods.
Vegetation
The investigated area is covered by forest with evergreen vegetation, which is dueto the good
and suitable climatic condition of this region. Throughout the field
area bushes are abundant with some fruit trees like mango, jackfruit, guava are alsonumerous.
Besides these tall trees like Garjan, Jarul, Shal, Shegun etc are notuncommon. The major
agricultural activity of this area is shifting cultivation, theyalso grow pineapple, ginger, turmeric
etc. It is preferred in high steep hill ranges where pineapples, ginger, turmeric etc. in lowhill
ranges. Both Sedentary and Jhuming cultivations are practiced here.

7. Tectonics
The Sitapahar anticline is the most prominent structure of the investigated area which axis is
trending NNW-SSE direction along the main structure of the Chittagong – Tripura Folded Belt
(CTFB). This doubly plunging anticlinal structure is about 400km long and 12-15 km wide and
major part of the western flank is steeper than the eastern flank. The western flank dips in an
angle ranging from 400 to 850and the eastern flank shows dip ranging from 4-85◦ which indicate
that the anticline is an asymmetric anticline. From the attitude of the beds the anticline is
suspected as a plunging anticline. A regional fault is believed to run along the axis of the
structure which trend is North direction. The eastern side of the fault is acted as foot wall and the
western part acts as a hanging wall which indicate the presence of reserve fault at ManikChari
(Ferdouse 1999) which is at a few kilometer east of Ghagra. A normal faultis found at Sundari
Chara.

8. Stratigraphy:
The exposed Neogene succession represents an overall basinward progradationfrom deep marine
through shallow marine to continental fluvialenvironments.Based on regionally correlatable erosion
surfaces the entire succession (3000+ mthick) has been grouped into three composite sequences
C, B and A, from oldest toyoungest. (1) Unit C (lower unit, 71 m thick) is characterized by
several thin packets of turbidites and slumped beds contained within a muddy sequence. Theunit
is thought to have been deposited in a setting not far basinward from the base-of-slope. (2) Unit
B (middle unit, 291 m thick) is a monotonous muddy slopedeposit that contains some localized
zones of very thin-bedded turbidites. (3) UnitA (upper unit, 208 m thick) represents the
progradation of the first shoreface sand body on a 176-m-thick shelfal mud. Detailed bed by
bed measurements have beencarried out in all these units. A general litho-stratigraphic column of
the lower partof the Surma Group exposed in the Sitapahar anticline have been given in Fig 8.On
the basis of the overall regional tectonic setting discussed in Section 2, it isassumed that the trend
of paleo-coastline in the CTFB was oriented north – south. Alam (1995) documented a similar
paleo-coastline trend from paleocurrent analysisof the Surma Group in the Sitapahar Anticline.
The measured current directionsrepresent landward (eastward) and basinward (westward)
directions

9. Course of Karnaphuli River:
It has possibly maintained its older course keeping pace with the uplift of the hill ranges and can
be classified as an antecedent river. The Karnafuli is narrow and straight from Prankiang
towaggachhari along Kaptai-Chandraghona road. The straightness of the river is probably due to
a fault, which controlled the channel from Prankiang to Wagga. The main tributaries of the
Karnafuli are the kasalong, Chengi, halda and Dhurung on the right and the Subalong, Kaptai,
Rinkeong and Thega on the left.Flowing to the west through rangunia upazila and then
keepingraozan upazila on the north and boalkhali upazila on the south, it receives the waters of
the Halda river at Kalurghat just above the railway bridge.
There is a legend about the naming of the Karnafuli river. It says an Arakanese princess who fell
in love with a tribal prince of Chittagong was once enjoying a moonlit boatride on the river with
the prince. While admiring the reflection of the moon dancing on the rippled water surface, the
princess inclined slightly and a flower tucked in the hair over her ear by the prince suddenly fell
into the river. The princess was grief-stricken at losing the flower, which she held very dear as a
present from her charming prince. She immediately jumped into the river to retrieve the flower
but could not. Instead she was carried away by the fast-flowing current and vanished in the river.
The prince dived into the river to rescue the princess but in vain. Out of sorrow he drowned
himself in the river to unite with the princess after death. This tragedy gave the river its name
Karnafuli from the word 'karnaful' meaning 'flower adorning the ear'. The river is known to the
Marma tribe as the Kynsa Khyong.
Water Chemistry:
The river Karnafully is one of the Himalayan River originating from the Lushai Hills in India.
The catchments of the Karnafully and its allied streams cover 5,500 (14,000 sq km) square miles.
Water samples were collected from Karnafully River along different points and analyzed for
various physiochemical parameters during winter. Effects of industrial wastes, municipality
sewage and agricultural runoff on the river water were investigated. The study was conducted
between the Kaloorghat Bridge and Patenga estuary including Chittagong port. This is the most
polluted area due to the presence of many chemical fertilizers, iron, leather and pharmaceutical
industries. All these industries discharge their untreated toxic waste water directly into the river
Karnafully. The study involved determination of physical and chemical parameters of surface
water at different points. The mean values of water temperature, total suspended solids (TSS),
total dissolved solids (TDS), total solids (TS), turbidity, dissolved oxygen (DO), bio-chemical
oxygen demand (BOD), chemical oxygen demand (COD), pH, electric conductivity and total
alkalinity were 23°C, 365.87 mg/L, 8018.8, 8518.33 mg/L, 31.54 FTU, 1.55 mg/L, 6.65 mg/L,
13961 μs/cm, 247.47 mg/L, 560.27 mg/L and 4.8 mg/L respectively.

10. Bank stability and Discharge:
Karnaphuli (also spelt Karnafuli) is a river in the south-eastern part of Bangladesh.
Originating from the Lushai hills in Mizoram, India, it flows through Chittagong Hill Tracts
and Chittagong into the Bay of Bengal. A large hydroelectric power plant using Karnaphuli
river was built at Kaptai during the 1960s. The mouth of the river hosts Chittagong sea port,
the main port of Bangladesh. Legend has it that a princess from neighboring Arakan (now in
Myanmar) fell in love with a tribal prince of Chittagong. The lovers were once enjoying a
moonlit boatride on the river. While admiring the reflection of the moon dancing on the
rippled water surface, the princess leaned slightly and a flower tucked in the hair over her ear
by the prince suddenly fell into the river. The princess was grief-stricken at losing the flower,
which she held very dear as a present from her charming prince. She immediately jumped into
the river to retrieve the flower but could not. Instead she was carried away by the fast-flowing
current and vanished in the river. The prince dived into the river to rescue the princess but in
vain. Out of sorrow he drowned himself in the river to unite with the princess after death. This
tragedy gave the river its name Karnafuli from the word ‘karnaphul’ meaning ‘flower
adorning the ear’. The river is known to the Marma tribe as the Kynsa Khyong.
Hazards in the area related to river:
The rivers of Bangladesh are the worse victim of pollution, especially the rivers which stands in
the neighborhood of the Dhaka city is being polluted tremendously. Like many rivers in
Bangladesh, Karnaphuli is heavily polluted by agricultural runoff. Reducing the amount of
oxygen available and harming aquatic life in the river. In 2015, a train carrying oil crashed over a
tributary of the river. The spill caused environmental degradation. To save the river from the
encroachers and pollution as well as their existence, the sampan majhis organised a three-day
sampan khela (boat race) and Chantgaiya (Chittagong) cultural fair in the river Karnaphuli.
Sampan Majhi Kalyan Samity Federation (SMKSF) in association with Chattagram Anchalik
Sanskriti Academy (CASA) organised the events titled “We are boatmen of the river Karnaphuli
and we have pledged to save the river”.
The Kaptai Dam is the location of the Karnafuli Hydroelectric Power Station, constructed in
Kaptai in 1962 and the only hydro-electric power plant in the country. This dam occasionally
creates high water level as consequent to flood.