Post on 26-Feb-2023
29/09/2014
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NRG BESS Early Career Researcher Conferenceon
Biodiversity, Ecosystem Services and Sustainability
Presenting Author : Ali Mohammad RezaieResearch Associate & Graduate Student
Co-Authors : Dr. Munsur Rahman, Dr. Anisul Haque, Shah Alam , Ishtiaq Ahmed, Hafez Ahmed, Sumaiya, Md. NurulKadir, Muhammad Khalid Bin Siddique, Mansur Ali Jisan
A Preliminary Assessment of the Sources of Hydrological Services in the Coastal Mangrove Forest of the Sunderbans
Using Delft 3D And 1D HEC-RAS Models
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Background of the Study
• The Ganges–Brahmaputra–Meghna (GBM) the third largest freshwater outlet to the world’s oceans
• The Brahmaputra, after travelling about 1800 km through Tibet and India-the Ganges flows for about 2000 km through India, and enters through the western side of Bangladesh.
• The Ganges, Brahmaputra and Upper Meghna rivers join and flow into the Bay of Bengal as the Lower MeghnaEstuary.
Background of the Study
- Almost NO Primary data available
- The unique habitat of Sunderbandepends on the Hydrological regime
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Objective of the study
• Sources of the freshwater and saline water in the ?
• Dependence of the ecosystem services of the Sundarbanon the freshwater flows of the Lower Meghna estuary or Gorai River ?
• Change in salty to fresh environment inside Sundarban depending on the seasonality and flooding scenarios ?
Models Descriptions
• Model boundary contains the River Lower Meghna, Arial khan & Gorai in the up and Bay of Bengal near Sri-Lankan coast in the down.
• All major rivers in the southern part of Bangladesh is fitted by relatively finer grids.
• Minimum Grid Size: 400m x 400m (River)
• Maximum Grid Size: 5000 m x 5000 m (Ocean)
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Models Descriptions _Data Sources
• River Bathymetry Data-Bangladesh Water Development Board; ESPA DELTAS Bathymetry Survey
• Ocean Bathymetry Data - General Bathymetric Chart of the Oceans (GEBCO); 30 sec resolution
• Land elevation Data – Ministry of Water Recourses, CEGIS; 50m resolution
• Boundary Data – Bangladesh Inland Water Transport Authority, Bangladesh Water Development Board, NAOTIDE ocean tide generator
Model Validation_Delft3D
Calibration: Buriswar SW 20; Central Estuarine System
-1.00
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
3.00
4/29/2000 5/4/2000 5/9/2000 5/14/2000 5/19/2000 5/24/2000 5/29/2000 6/3/2000
MeasuredData
Model Data
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Model Validation
Calibration: Meghna Bhola SW 279; Eastern Estuarine System
0.00
0.50
1.00
1.50
2.00
2.50
3.00
25-Jan-2000 4-Feb-2000 14-Feb-2000 24-Feb-2000 5-Mar-2000 15-Mar-2000 25-Mar-2000 4-Apr-2000
Measured
Model
Model Validation
Calibration: Rupsa SW 288.4; Western Estuarine System
0.00
0.50
1.00
1.50
2.00
2.50
12-May-2000 14-May-2000 16-May-2000 18-May-2000 20-May-2000 22-May-2000 24-May-2000 26-May-2000 28-May-2000
Measured
New
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HEC-RAS Model Validation
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
0.008 0.01 0.012 0.014 0.016 0.018 0.02
NR
MSE
(%
)
Roughness
Whole Year
Dry Season
Wet Season
Model Performance for different roughness
HEC-RAS Model Validation
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
0.008 0.01 0.012 0.014 0.016 0.018 0.02
NM
AE
(%)
Roughness
Whole Year
Dry Season
Wet Season
Model Performance for different roughness
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Results & Discussions
The discharge, total water volume and percentage of flow distribution among the estuarine systems
Results & Discussions
total water volume and percentage of flow distribution among the estuarine systems
Estuarine Systems Estuary
Total Dry Season Flow m3 (Nov-
April)
Total Wet Season
Flow m3 (May-
Oct)
Eastern Estuarine System
(EES) Meghna 66471(59%) 377285 (87%)
Central Estuarine System
(CES)
Arail Khan 930 (1%) 3897(1%)
Bishkhali 149 (0.5%) 211(<1%)
Baleshwar 19572 (20%) 22761 (6%)
Western Estuarine System
(WES)
Rupsa 3701(4.5%) 3021 (1%)
Shibsa 14023 (15%) 13823 (4%)
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Discharge distribution in the estuarine systems on an average
flooding conditions
79%
7.5% 0.5% 1%
3% 3%
6%
Results & Discussions
The model results show that the freshwater source of Sunderban is from Lower
Meghna; from eastern estuarine system to western !
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Tidal characteristics
0
0.5
1
1.5
2
2.5
3
0 20 35 55 70 85
Velo
cit
y (
m/s
)
Distance from upstream (km)
Meghna ( Ebb dominating)Flood
Ebb
Meghna (Eastern Estuary)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 5 20 35 45 60 70 90
Velo
cit
y (
m/s
)
Distance from upstream (km)
Rupsha pasur (Flood dominating) Flood
Ebb
Rupsha- Sibsa
(Western Estuary; Sunderban)
Tidal Excursion
Tidal Excursion for all estuarine Systems for an average Year (Dry season)
Flooding Condition/ Season
Dry Season
Wet Season
Average
Extreme Dry
ExtremeWet
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Tidal Excursion
Tidal Excursion for all estuarine Systems for an average Year (Wet season)
Tidal Excursion
Tidal Excursion for all estuarine Systems for an extreme wet Year (Dry season)
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Tidal Excursion
Tidal Excursion for all estuarine Systems for an extreme wet Year (Wet season)
Tidal Excursion
Tidal Excursion for all estuarine Systems for an extreme dry Year (Dry season)
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Tidal Excursion
Tidal Excursion for all estuarine Systems for an extreme dry Year (Wet season)
Tidal Prism for all estuarine systems for an Extreme Wet year
0.000E+00
5.000E+11
1.000E+12
1.500E+12
2.000E+12
2.500E+12
3.000E+12
3.500E+12
MEGHNA TENTULIA BURISHWAR BISKHALI BALESHWAR RUPSA SIBSA
Wet Season
Flood Volume Ebb Volume
0.000E+00
5.000E+11
1.000E+12
1.500E+12
2.000E+12
2.500E+12
3.000E+12
3.500E+12
MEGHNA TENTULIA BURISHWAR BISKHALI BALESHWAR RUPSA SIBSA
Dry Season
Flood Volume Ebb Volume
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Tidal Prism for all estuarine systems for an Extreme Dry year
0.000E+00
5.000E+11
1.000E+12
1.500E+12
2.000E+12
2.500E+12
3.000E+12
3.500E+12
MEGHNA TENTULIA BURISHWAR BISKHALI BALESHWAR RUPSA SIBSA
Wet Season
Flood Volume Ebb Volume
0.000E+00
5.000E+11
1.000E+12
1.500E+12
2.000E+12
2.500E+12
3.000E+12
3.500E+12
MEGHNA TENTULIA BURISHWAR BISKHALI BALESHWAR RUPSA SIBSA
Dry Season
Flood Volume Ebb Volume
Tidal Prism for all estuarine systems for an average year
0.000E+00
5.000E+11
1.000E+12
1.500E+12
2.000E+12
2.500E+12
3.000E+12
3.500E+12
MEGHNA TENTULIA BURISHWAR BISKHALI BALESHWAR RUPSA SIBSA
Wet Season
Flood Volume Ebb Volume
0.000E+00
5.000E+11
1.000E+12
1.500E+12
2.000E+12
2.500E+12
3.000E+12
3.500E+12
MEGHNA TENTULIA BURISHWAR BISKHALI BALESHWAR RUPSA SIBSA
Dry Season
Flood Volume Ebb Volume
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Tidal Prism at Discrete Estuarine System
Tidal Prism/ Flood-Ebb dominance for all estuarine Systems for an Average/
Representative Year
Preliminary Findings
• More than 80% of the total flow volume and discharge are draining out
through Lower Meghna in almost every conditions ( Average; Dry; Wet)
• the ecosystem services of the Sundarban depend on the freshwater
flows of the Lower Meghna estuary entering from the ocean side
• The computed tidal excursions and tidal prisms shows that the strength
of ebb and flood tides are almost same for the Sundarban system.
• So, the freshwater entering through the ocean during the flood tide are
completely drained during the ebb tide that results a rhythmic change of
salty to fresh environment inside Sundarban depending on the
seasonality and flooding scenarios.
• This will support co-existence of both freshwater and saline water
fisheries and other fluvial and marine habitats in Sundarban.
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Implications for ecosystem services
• Mangroves are key source of income for poor rural populations
• Mangroves also offer a range of supporting services, especially
protection against cyclones, erosion etc.
• Mangroves are dependent on a delicate salinity balance
• Sea level rise and upstream dams will reduce freshwater
availability
• Understanding current interactions between saline and fresh
water will help protect these already threatened resources.
• Change in the dynamic equilibrium due to either natural or man-
made will adversely affect the services of these particular
ecosystem resources of Sundarban.
Present Research Gap
Data:• Availability of accurate and time series data• Open access data
Design: • Interdisciplinary research designs are rare but required
Research:• Numerical quantification of river-sea flow dynamics,
morphological changes, hydrological regime dynamics• Affect of physical processes on ecosystem services• Impact of coastal hazards on biodiversity
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On-going work and Future Plan
- Upload results for open access
- Further analyse links between ecosystem resources, coastal morphological changes and extreme events.
- Further investigate the links between natural hazards and ecosystem services
Acknowledgements
• BUET IWFM research team who have had direct and indirect input to this study.
• Espa Deltas project (part of the ESPA programme)for funding this study.