Abstract:
The erosion and shifting of river courses. loss of land, especially along the Jamuna river have
long been recognized as a national problem that affect8 a _,izablepopulation in Bangladesh.
To mitigate the river bank erosion llWl)fj ha.~initiated a 20 km capital dredging on the River
Jamuna as pilot basis in order!o guide the flowto reduce the risk of failure ofSirajganj Hard
Point and right guide bundh of the Bangabandhu Bridge. This study would be u~efult() assess
th~ role of capital dredging in comprehensive riv~r management plan as well as the
morphologi~al stability of an artificial dredged channel along the braided Jamuna river of
Bangladesh. The sustainability of the dredged channel "as assessed by analyzing the timeseries
satellite images, cross-section comparison, sediment concentration and depth average
velocity. Geo-refereneed satellite image of ASTER and IRS LJSS from 2007 to 2012 ha.,
been superimposed to a,,,,,,s!he sand bar movement. During 2007 !o 2012, lateral movement
of Sandbar-l (upstream of Sirajganj Hardpoinl) ranges from 800m to 1870m wher~as for
Sanbar-2 (dowm,tream of Sirajganj Ilardpoint) ranges from 560m to 1060m, At the 8am~
tim~, .the longitudinal movement of Sandbar-] ranges from 150m to 600m whereas for
Sandbar-2 l'"dIlgestrom 300m to 1400m. It is observed that, the channel is devdoping very
fast along the western bank through deviation of flow l"warus the river banle It's is also
obsened !hatlhe rate of bar translation is high and it may cause tbe siHalion of the dredged
channel. Compariwn of cross-section indicales that there is no sigaificant positive impad of
dredging has observed ncar Simjganj Harupoint area as well 8S tbe downstream of
Hanghabhandhu Bridge. It i, also observed that the rate of siltation is higher, where the
dredging alignment passes through the exisling char. It was happening, because Ihe hydraulic
condition around the dredged area as well as ups!rcam river morphology remain favorable for
the siltation on the existIng ehllr. Analysis ofobscrved data indicates that, more than 1.75 m/s
flow velocity persist, during the peuks which covering the entire Sirajganj Hardpoint area
and it persists from mid of May to September. AnaJysi, of sediment concentration and depth
average velocity indicates thaI <;edimentconcentration at particular depth and velocity plays
an important role in the em,ion or deposition process along the study reach. It is found lhat at
a particular point under or over sediment concentration with respect to the sediment transport
capacity cause ~ilhcr erosion or deposilion. The major fUiding of this study i~ that the
dredging of a braided river would not be a sustainahle solution without changing upstream
ri,~r morphology as well as hydraulic conditions. It is also observed that, if the dredging
alignment pa'8e, through the exisling ~hannel not over the char area, the dredgoo channel
would be more sustainable.
