Potential hydrogeological, environment and vulnerability to pollution of the ...
Presentation_DUET-AH
1. Title
Impacts of Coastal Floodplain Sedimentation on Net
Subsidence in the Ganges-Brahmaputra-Meghna
Delta
Authors
MD. WASIF-E-ELAHI
ANISUL HAQUE
MUNSUR RAHMAN
NOOR HOSNA
International Conference on Recent Innovation in Civil Engineering for Sustainable Development (IICSD-
2015)
ID: WRE-047
2. INTRODUCTION
Bangladesh is located in the lower part of Ganges basin.
The coastal floodplain of Bangladesh consists of three major river
systems: the Ganges, the Brahmaputra and the Meghna (GBM).
GBM delta is the most active delta where erosion and sedimentation
process is very dynamic.
Subsidence is the normal process in deltas and is caused by a multitude of
natural processes, which are often increased by anthropogenic reasons.
3. INTRODUCTION
In literature, subsidence rates are found to be reported either over the whole
delta or regionally and at specific locations.
For the whole GBM delta, Ericson et al. (2006) reported a rate of up to 10mm/yr
(no time period specified).
Regionally, Khan and Islam (2008) stated 3 mm/yr for the lower delta (no time
period de- fined).
Schiermeier (2014) reported up to 9mm/yr of subsidence in the western delta,
and up to 4 mm/yr in the east.
Ostanciaux et al. (2012) reported subsidence of 12.3mm/yr in the western delta
and uplift of 3.6 mm/yr in the eastern delta during an unspecified period
between 1993 and 2009.
4. INTRODUCTION
Brammer (2014) mentioned overall maximum mean rate of subsidence in
western region as 2.5 (mm/year) which is assumed constant over the GBM delta.
No study has yet been performed by considering sedimentation as a counter-
measure to sedimentation
In this paper, the combined effect of sedimentation and subsidence are taken
into account to compute the changes of net land elevation.
5. STUDY AREA
WES: Western Estuarine System
Gorai-Rupsa-Pasur river systems
CES: Central Estuarine System
Baleswar-Bishkhali-Buriswar river
systems
EES: Eastern Estuarine System
Meghna-Tentulia-Lohalia river
systems
6. THE MODEL
Year 2000 is considered as the base year
The open source Delft3D morphology model is applied in the study
region to compute the floodplain sedimentation.
By comparing the simulated elevation of floodplain with the base
year elevation, the net sedimentation rate in the floodplain is
computed.
9. River
name
Station name Measured erosion/deposition
rate (cm/month)
(For a long Period of data which is
more than 10 years)
Model
erosion/deposition
rate (cm/month)
(Only for the base year
condition)
Reliability %
Bishkhali
(CES)
BIS16 -0.0122 0.1912 49.26
BIS15 -0.1426 -0.1504
BIS14 -0.4637 -0.4430
BIS12 0.3157 0
BIS11 0.0083 -0.0837
Lower
Meghna
(EES)
ML2 -0.7832 0 41.80
ML5 0.2265 -0.0023
M12 -0.2471 -0.0010
Rupsa
(WES)
RP10 -0.9200 -0.2532 50.86
RP13 -0.6169 -0.3153
RP14 (n/a) -0.3492
Overall Model reliability over the estuarine systems 47.30
MODEL VALIDATION
17. RESULT AND DISCUSSION
Possible impact of sea level rise:
From literature, in Bangladesh coast, during the period from 1977 to 1998, the
observed trend of change of sea level shows a sea level rise of 5.05 mm/year to 7.4
mm/year.
If these values are considered to be valid till the end of century, net uplift in the
eastern and western region will largely compensate the effect of sea level rise in
these regions.
The central region will be aggravated due to net subsidence
18. CONCLUSION
• Net land elevation of the GBM delta is computed by using sedimentation and erosion rates and
superimposing these values on the constant subsidence rate of 2.5 mm/year.
• The net land elevation was subsiding at the beginning of the century for all the region.
• During the end of the century, both the eastern and the western region will continue rising at
different rates, but the central region, during this entire time horizon, will be subsiding.
• These might have significant effect to offset sea level rise effect in the eastern and western
region.
• The central region, on the other hand, will remain vulnerable as a possible victim of sea level rise
effect.
19. ACKNOWLEDGEMENT
We would like to acknowledge to NERC, ESRC, UK DFID, ESPA for
funding this work as part of the ESPA Deltas project (Grant Reference
Code : NEJ0027551). We would like to acknowledge the contribution of
all the members associated with the research team who has direct and
indirect input to this article.
