FISH SPECIES AROUND RIVERBANK PROTECTION STRUCTURE AT SIRAJGANJ

Presented By:

Mahmud Hasan Tuhin

Research Assistant

IWFM

BUET

Presentation outline

Background

Study area

Structure around Sirajganj town

Methodology

Results

Conclusion and Recommendation

2

Background

Construction of bank protection structures have modified the flow

regime.

Changes in river flow regimes are well recognized as a cause of

changes to river geomorphology and habitat.

Change in flow regime and also change the river habitat and biota.

The change in flow regime might introduce alien species, have had a

dramatic, negative impact on native fishes.

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Background

4

Different erosion protection

structures such as Groyen, Spur,

Revetment, Hardpoint are common.

River Jamuna has all of these

structures makes it as a highly

trained river

The right bank have the

maximum numbers of the

structures.

Figure: Schematic Diagram of structures

of Jamuna River

Study Area

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Jam

un

a R

iver

Sirajganj Hardpoint

Bangabandhu Bridge

Guide Bund

Sirajganj Town

Sirajganj Hardpoint is situated at the east

side of the Sirajganj town and the right bank

of the Jamuna river.

Bangabandhu Bridge is located 7 kilometer

south (Downstream) of the hard point.

Figure: Sirajganj town and Jamuna river

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Study Area

Sirajganj Hardpoint from different view point

Upstream termination of Hardpoint from upstream side

Upstream termination of Hardpoint from downstream side

Revetment work of Hardpoint Revetment work of Hardpoint

Methodology

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Social analysis(Primary data)

Ecological analysis (Primary data)

Technical analysis(Primary data and Secondary data)

Socio-eco-technical approach

Focus Group Discussion (FGD) with

fishers

Key informants interview (KII)

On spot species identification

On spot species change information

collection

Aquatic Doppler current profiler (ADCP)

data

Bathymetric data

On site float track data

Methodology

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KII

FGD

Float TrackOn site observation by Research team

Species identification

Results

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Flow pattern near the Sirajganj hard point

Figure : Primary vortex and secondary vortex in scour hole around Sirajganj hard point

The flow pattern continuously changes due to changing morphology of sand bars,

roughness and the configuration of the bank protection structure.

The velocity adjacent to the hard point is doubled of the approach flow velocity. It

is also evident that the deep scour hole is located near the upstream of hard point.

Clock wise and anti clock wise vortices creates deep scour hole near the

structure.

(Source: Modified from Nazim et. al, 2010)

Results

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Analysis of float data of Sirajganj hard point

Figure: Flow velocity near Sirajgonj hard point

GPS float track data

It is seen that the water velocity

suddenly increased (>2.5 m/s) at

the upstream of the hard point

marked by the dotted arrow .

High velocity was observed up

to one kilometer downstream from

the upper termination

After one kilometer down stream

of the upper termination, the

velocity decreased (between 1 to

2.5 m/s) and marked by the solid

arrow.

(Source: Field Study, 2010)

Results

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Analyses of bathymetric data of Sirajganj hard point

Figure: Rapid formation of scour holes near hard point

Deep scour hole formed near the upper termination of the hard point. Along

the revetment work, several deep scour holes were found in several places.

10 day interval bathymetric data shows that, deep scour hole formed. These

scour holes also moved with time and with the change of the river flow.

(Source: BWDB Field Survey, 2010)

Date: 6 June, 2010) Date: 17 June, 2010)

No Scour Hole Deep Scour Hole formed

Results

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Change in fish habitat

Causes of fish species change

Change in flow pattern, river bathymetry, water velocity, formation of

deep scour hole etc. affect the natural habitat of the river.

Species like small and carp prefer low velocity for their grazing,

migration and wandering.

Some species like Catfish, prefer high velocity and deep scour holes

for their resting, grazing and drifting.

After construction of the hard point, the velocity of the river near the

adjacent of structure have increased.

Deep scour holes formation, shifting of river bed and other

morphological changes directly affect the fish habitat.

(Source: Field Study, 2010)

Results

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Change in fish species for habitat change

(Source: Field

Study , 2010)

Name of dominant species

Position after construction before construction

*1Air (Sperata aor) Rui (Labeo rohita)

2Baghair (Bagarius bagarius) Catol (Catla catla)

3 Kalbaus (Labeo calbaus) Ilish (Tenualosa ilisha)

4Pangas (Pangasius pangasius) Air (Sperata aor)

5Boal ( Wallagu attu) Baghair (Bagarius bagarius)

6Mrigal (Cirrhinus mrigala) Boal ( Wallagu attu)

7 Rita (Rita rita) Puti (Puntius sophore)

8Khorsula (Rhinomugil corsula) Kajuli (Ailia coila)

9 Ilish (Tenualosa ilisha) Mrigal (Cirrhinus mrigala)

10Ghaura (Clupisoma garua)

Chingri (Shrimp) (Macrobrachium

rosenbergii)

11 Gang Tengra (Gagata cenia) Bailla (Awaous guamensis)

Table : Major fish species found near the Sirajganj hard point

Change in Fish composition before and after construction of the hardpoint

AvailabilityHigh

AvailabilityLow

Results

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Change in fish species for habitat changeChange in Fish composition

Figure : Change in fish composition near hard point (Source: Field Study, 2010)

Available fishes are divided into four major groups

Catfish group containing Air (Sperata aor), Baghair (Bagarius bagarius), Pangas

(Pangasius pangasius), Boal (Wallagu attu), Rita (Rita rita), Ghaura (Clupisoma garua),

Gang Tengra (Gagata cenia);

Carp fish group containing Rui (Labeo rohita), Catol (Catla catla) Mrigal (Cirrhinus

mrigala);

Small fish group containing Puti (Puntius sophore), Kajuli (Ailia coila), Chingri (Shrimp)

(Macrobrachium rosenbergii), Bailla (Awaous guamensis), Khorsula (Rhinomugil corsula);

Ilish (Tenualosa ilisha) as an independent group

Results

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Some Catfish species caught around the hardpoint

Air

Boal

Kalbaus

Rita

Baghair

(Source: Field Study, 2010)

Results

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Local fishers knowledge about habitat change near Sirajganj hard point

Low water velocity of the river was observed before the bank protection

structure, because the river was wider and deeper with fewer sandbars.

After the construction of hard point, formation of high sand bars (Char land) has

increased. “Ulta oure” (back flow), “Ghona” (deep hole / scour hole), “Dhar” (High

velocity) etc. have also increased than earlier time.

Large cat fish species prefer deep places of river bed for resting, so they take

rest inside the Ghona.

Small fish cannot swim against the high velocity near the hard point and they

trapped inside the strong return flow. At that time large catfish species hunt them.

Some time a good number of large fishes is caught by the fisher near the hard

point, but it doesn’t indicate that the place is fish friendly habitat but rather a

natural trap for fishes.

(Source: Field Study, 2010)

Conclusion and Recommendation

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Riverine structure induced morphological and hydraulic changes

modify the natural fish habitat of the river.

For such alteration of the habitat, available species are also

changed.

After construction of Sirajganj hard point, cat fish species like Air,

Baghair and Kalbaus have replaced the previously common carp

species like Rui and Catol.

The availability of predator fish species has also increased near

the hard point area.

The design and planning of future interventions would need to be

modified in order to maintain natural fish habitat.

Fish friendly and eco friendly bank protection structures should

introduced for the river training works.

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THANKS TO ALL