29/09/2014

1

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

29/09/2014

2

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

29/09/2014

3

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)

29/09/2014

4

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

29/09/2014

5

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

29/09/2014

6

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

29/09/2014

7

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%)

29/09/2014

8

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 !

29/09/2014

9

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

29/09/2014

10

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)

29/09/2014

11

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)

29/09/2014

12

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

29/09/2014

13

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

29/09/2014

14

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.

29/09/2014

15

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

29/09/2014

16

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.

29/09/2014

17

Thank You All !

“The scientist is not a person who gives the right answers, he's one who asks the right questions.”

― Claude Lévi-Strauss

For further Query : rezaie06buet@gmail.com