摘要：The Government of Bangladesh has planned to make a large
build up area (BUA) in a newly developed sedimentary point bar (locally
known as ‘Char’) at Lebukhali along the northern bank of Payra river in
the southern part of the country. From a study it was revealed that, this
sedimentary bar has to be raised by 3.45 meters from MSL to keep it free
from any extreme events (like tidal and storm surge effects) for 100 years
return period. Accordingly, it was planned to collect the required filling
material (estimated 57.6 million m3 of sand/soil) by dredging the same
river bed. In Bangladesh dredging of river is very popular and widely
undertaken to collect filling and construction material, but its adverse
impact on river bed, bank and adjacent areas are hardly probed. This study
aimed at analyzing the adverse impacts of dredging from Payra River bed.
Four alternative sand bars have been identified as dredging area at varying
distances located both upstream and downstream of the proposed site. The
dredging impacts were analyzed for different boundary conditions. The
study is based on physical survey (topographic and bathymetric surveys),
historical data and numerical model analysis. Numerical model is applied
through Delf 3D to investigate the impact on flow parameters: flood depth
and velocity magnitude. Continuous field visit and observations were made
through last one year to observe real impact. The analysis revealed that
dredging of any of the bars have resulted changes in flow field. The
distance of dredging point does not control the flow field rather the
dredging volume, depth and upstream conditions determine the effect on
bank erosion. As such, the dredging locations have been prioritized
considering the least possible effects on river bank erosion and founded
that little erosion is taking place for both upstream and downstream region.
However, the long term impacts in other areas of the river need to be
investigated as the time pass.
其他摘要：The Government of Bangladesh has planned to make a large build up area (BUA) in a newly developed sedimentary point bar (locally known as ‘Char’) at Lebukhali along the northern bank of Payra river in the southern part of the country. From a study it was revealed that, this sedimentary bar has to be raised by 3.45 meters from MSL to keep it free from any extreme events (like tidal and storm surge effects) for 100 years return period. Accordingly, it was planned to collect the required filling material (estimated 57.6 million m3 of sand/soil) by dredging the same river bed. In Bangladesh dredging of river is very popular and widely undertaken to collect filling and construction material, but its adverse impact on river bed, bank and adjacent areas are hardly probed. This study aimed at analyzing the adverse impacts of dredging from Payra River bed. Four alternative sand bars have been identified as dredging area at varying distances located both upstream and downstream of the proposed site. The dredging impacts were analyzed for different boundary conditions. The study is based on physical survey (topographic and bathymetric surveys), historical data and numerical model analysis. Numerical model is applied through Delf 3D to investigate the impact on flow parameters: flood depth and velocity magnitude. Continuous field visit and observations were made through last one year to observe real impact. The analysis revealed that dredging of any of the bars have resulted changes in flow field. The distance of dredging point does not control the flow field rather the dredging volume, depth and upstream conditions determine the effect on bank erosion. As such, the dredging locations have been prioritized considering the least possible effects on river bank erosion and founded that little erosion is taking place for both upstream and downstream region. However, the long term impacts in other areas of the river need to be investigated as the time pass.
