G4: Assessment of the Impact of Anticipated External Drivers of Change on Water Resources of

the Coastal Zone

Ganges Basin Development Challenge

1. What are the key drivers of change in the hydrology and performance of the system?

2. What are the effects of anticipated changes on flooding, submergence, sedimentation, salinity intrusion and water availability in the different polders of the coastal zone?

3. What are the implications of adaptation strategies for different anticipated changes?

4. What are the implications of policy changes and its applications to cope with anticipated changes? What strategies can be put in place to influence policy makers and stakeholders to adapt to anticipated changes?

Research Questions

Overall Methodology

Assessment of the impact of anticipated external drivers of change on water resources of the coastal zone

Data, Maps on fresh water availability, Salinity, Improved drainage and storage plan, storm surge risk assessment in present & future condition

Up-scaling to LGED, WARPO, BWDB, DoE,,BADC,DAE Planning Commission and Climate Change Cell Involving G5

Simulation of Scenarios

Population projection and water requirement

Land use change

Climate change projection

Trans-boundary flow analysis

Defining Study Area Field Survey and Data Collection

Literature ReviewWater Flow and Salinity Modelling

(MIKE&SWAT)Model DevelopmentCalibration Validation

Simulation of Baseline Condition

Selection of ScenariosInvolving Gs and

Stakeholders

Selection of Drivers of Change

Involving Gs and other Stakeholders

Ou

tco

me

Lo

gic

Mo

de

lOUTCOMES

Change in KAS Change in Practice/ behavior

ImpactProject outputs

Existing condition:

• Data on WL, Flow, Salinity

•Digital Elevation Model

• Freshwater & salinity zoning map

• Drainage Conditions and Inundation maps of polders

Use of data, information & knowledge

Understanding external drivers, scenarios and their effects

Use of data & information

Development of new database

Future condition:

• Climate change projections

• Population projection

• Landuse change projection

• Freshwater & salinity zoning map

• Drainage Conditions and Inundation maps of polders

•Cyclone induced storm surge level and embankment crest level

• Improved Drainage plan of the three polders

Improved and resilient water

infrastructure and operation

Improved Polder management for

maximizing crop & fish production and minimizing inundation risk

Researchers of G1, G2, G3 & other ongoing projects

Acquiring new information & knowledge

Understanding the benefits of using new information

and improved plan for proper drainage and

irrigation

Improved planning, design and

implementation

BWDB, WARPO, LGED, DOF,BADC,FAO and NGOs

Understanding of effects of external drivers

Motivated and encouraged to use the

new information

Assimilation of new knowledge and

information in project planning and

approval and policy change

Ministry of Water Resources, Ministry ofAgriculture, Planning Commission

• External drivers

• Scenarios

Outcome Logic Model

Study Area:

Ganges Dependent Area in Bangladesh

Coastal Divisions: Barisal: Patuakhali, BargunaKhulna: Khulna & Satkhira districts

Project Target Area:Coastal Zone of the Ganges basin in Bangladesh except the Sundarbans

Polders: 3 (Satkhira), 30 (Khulna), 43-2F (Patuakhali)

Polder-3High Salinity

Polder-30Medium Salinity

Polder-43/2FLow Salinity

Coastal Zone of the Ganges Basin in Bangladesh

Study Area

Data Collection and Analysis

Primary DataSalinity in the adjacent rivers and in the khals inside the Polders Cross section survey of rivers & khals of the three polders Water level measurement in the khals & adjacent rivers Water flow measurement (tidal) in the adjacent rivers Topography & land use survey inside the polders Structural information of drainage and flushing regulators Salinity measurements at additional 31 stations in southwest region of Bangladesh Operation log and flow of the regulators and water level in khals and floodplain

Secondary Data Salinity, water flow, rainfall, evaporation data from BWDB Water level data from BIWTA Climate data from BMD and IMD grid Mouza layers, growth center locations from LGED Population census data from BBS Agriculture and irrigation data from DAE, IRRI River cross-sections, land topography, polder, road and such other data from IWM database

Digital Elevation Model from Land Level Survey

Polder 3

Polder 30

Polder 43/2F

Rabi (Boro) Kharif-2 (T. Aman) Kharif-1 (Aus)

2 PPT

Salinity and Available flow in Payra River

Salinity variation and Flow availability : Polder 43/2F

Rabi (Boro) Kharif-2(T. Aman) Kharif-1(Aus)

2 PPT

Salinity and Available flow in Kazibacha River

Salinity variation and Flow availability : Polder 30

2 PPT

Rabi (Boro) Kharif-2 (T. Aman) Kharif-1(Aus)

Salinity in Ichamoti River

Salinity variation : Polder 03

Spatial Variation of Salinity in the Coastal Ganges in Bangladesh

May, 2012 Base Year: 2012

KHULNA

BARISAL

Monthly Salinity variation with upstream freshwater flow

External Drivers of Change

Final List of Key External Drivers and Their Ranking

Scenario Generation

Scenario Generation Workshop

Combination of Drivers

Scenarios

• Scenarios developed in a participatory approach

• Done collectively by experts, policy makers, service providers, practitioners, and stakeholders

• Examined different combinations of external drivers as likely scenarios

• 14 scenarios selected initially• Further consolidated into 5

scenarios

Scenario: Effect of Transboundary flow and Climate Change

Ganges Basin

Upstream Boundaries (Q, Sal = 0pt)Minimum and maximum flow in Gorai in dredged condition

Downstream Boundaries (WL, Sal) + Sea Level Rise

Transboundary flow Best case scenario: maximum flow since GWTWorst case scenario: minimum flow since GWT

Climate change: A1B condition (Precipitation, Temperature and Sea

Level Rise)

Scenario : 2030

Scenario: Transboundary Flow, Land-Use Change and Climate Change

Ganges Basin

Land-use change

Climate change: A1B and A2 conditions (Precipitation, Temperature and Sea

Level Rise)

Scenario : 2030

Transboundary flow Best case scenario: maximum flow since GWT

Upstream Boundaries (Q, Sal = 0pt)Minimum and maximum flow in Gorai in dredged condition

Downstream Boundaries (WL, Sal) + Sea Level Rise

Scenario: Effect of Multiple Drivers on Water Resources

Ganges Basin

Transboundary flow (worst case scenario: minimum flow since GWT)

Population growth: water extraction from the river system

Climate change: A1B condition (Precipitation, Temperature and Sea

Level Rise)

Scenario : 2030

Land-use change

Downstream Boundaries (WL, Sal) + Sea Level Rise

Upstream Boundaries (Q, Sal = 0pt)Minimum flow in Gorai in dredged condition

Scenario: Effect of Multiple Drivers on Water Resources

Ganges Basin

Downstream Boundaries (WL, Sal) + Sea Level Rise

Transboundary flow (best case scenario: maximum flow since GWT)

Population growth: water extraction from the river system

Climate change: A1B condition (Precipitation, Temperature and Sea

Level Rise)

Scenario : 2030

Land-use change

Upstream Boundaries (Q, Sal = 0pt)Maximum flow in Gorai in dredged condition

Scenario: Infrastructure Development

Ganges Basin

Land-use change

Transboundary flow (best case scenario: maximum flow since GWT

Population growth: water extraction from the river system

Climate change: A1B condition (Precipitation, Temperature & Sea Level Rise)

Scenario : 2030

Change in water management practices

Change in water governance and institutions (including policy change)

Water infrastructure development

Downstream Boundaries (WL, Sal) + Sea Level Rise

Upstream Boundaries (Q, Sal = 0pt)Minimum flow in Gorai in dredged condition

Driver: Transboundary FlowTransboundary Flow

1. Hisna ~ Mathavanga ~Kobadak ~ Kholpetua

2. Kobadak ~ Sibsa

3. Bhairab ~ Rupsa ~ Pussur

5. Gorai ~ Nabagonga ~ Atai ~ Rupsa ~ Pussur

6. Gorai ~ Madhumati ~ Baleswar

4. Gorai ~ Rupsa ~ sholmari ~ Sibsa

7. Arial Khan ~ Baleswar

8. Arial Khan ~ Biskhali

9. Arial Khan ~ Buriswar

Driver: Infrastructure development (Ganges Barrage)

Ganges Barrage

230 m3/s

182 m3/s

National Land Zoning Map : Ministry of Land

May2012, Base condition with maximum Transboundary flow under Ganges Treaty

Effect of Transboundary Flow :South-west Zone of Bangladesh

May2012, Base condition with minimum Transboundary flow under Ganges Treaty

Effect of Transboundary Flow :South-west Zone of Bangladesh

May, 2030 climate change (A1B) with minimum Transboundary flow under Ganges Treaty

Effect of Climate Change and Transboundary Flow: South-west Zone

May, 2030 Climate change (A1B) + Transboundary flow with Ganges Barrage

Effect of Infrastructure Development: Ganges Barrage

Effect of Drivers: Trans-boundary flow, Climate Change and Ganges Barrage

Effect of Drivers: Trans-boundary flow, Climate Change and Ganges Barrage

Effect of Drivers: Trans-boundary flow, Climate Change and Ganges Barrage

Effect of Drivers: Trans-boundary flow, Climate Change and Ganges Barrage

Effect of Drivers: Trans-boundary flow, Climate Change and Ganges Barrage

Decrease of Freshwater and mild brackishwater area (0-2ppt):Transboundary flow: 1100 sq. kmClimate Change: 800 sq. km

Base (2012)

(Sq Km)

Max TBF

(Sq Km)Change

(%) Min TBF (Sq Km)

Change (%)

Climate Change (SLR) (Sq Km)

Change (%)

Min TBF+SLR (Sq Km)

Change (%)

Effect of Drivers: Trans-boundary flow, Climate Change and Ganges Barrage

Exposure of area under more than 2ppt salinity

Barisal Division 1574 1571 0.2 1588 0.9% 1708 8.5% 1722 9.40%

Khulna Division 11420 12179 6.6% 13144 15.1% 12094 5.9% 13818 21.00%

Base (2012) (Sq Km)

Ganges barrage+ SLR Change (%)

(Sq Km)

Khulna Division 11420 11142 (-3%)

Infrastructure development: Ganges Barrage

3 day Depth-Duration Map Flood type Area (sqkm) % of Area

Flood Free 25.48 40

F0 (0 - 30 cm) 21.01 33

F1 (30 - 90 cm) 13.42 20

F2 (90 - 180 cm) 4.32 7

Drainage Performance of Polders at Present and Future

POLDER 30

3 day Depth-Duration Map(Scenario_2030)

Flood type Area (sqkm) % of Area

Flood Free 21.97 34

F0 (0 - 30 cm) 22.24 34

F1 (30 - 90 cm) 15.26 24

F2 (90 - 180 cm) 5.03 8

Drainage Performance of Polders at Present and Future

POLDER 30

3 day Depth-Duration Map(Scenario_2050)

Flood type Area (sqkm) % of Area

Flood Free 13.54 21

F0 (0 - 30 cm) 16.41 25

F1 (30 - 90 cm) 27.86 43

F2 (90 - 180 cm) 6.70 11

Flood type2030

(Change from present condition)2050

(Change from present condition)

Flood Free -6 -19

F0 (0 - 30 cm) 1 -8

F1 (30 - 90 cm) 4 23

F2 (90 - 180 cm) 1 4

Drainage Performance of Polders at Present and Future

%%

%

%

%

%

%

%

POLDER 30

• Dredging and Re-excavation of rivers and khals

• Additional drainage structure

Drainage Improvement Measures

Polder-30: Case Study- Maitbhanga Village

Discussion with local people of Maitvanga about drainage The high depth of water in Aman field of Maitvanga beel

Drainage canal has been silted up and the bottom level has been same as the surrounding land

Drainage canal blocked by human intervention

UP road crosses the canal without any culvert blocking

cross-drainage

Polder-30: Subpoldering and Community based Water Management

0 1000 2000 3000 4000 50000

0.5

1

1.5

2

Distance (m)

Land

Lev

el (m

PWD

)

0 1000 2000 3000 4000 5000-0.5

0

0.5

1

1.5

2

Distance (m)

Land

Lev

el (m

PWD

)

0 1000 2000 3000 4000 5000-0.5

00.5

11.5

2

Distance (m)

Land

Lev

el (m

PWD

)

Considerations for Sub-polderization: Land level

Considerations for Sub-polderization: Land level Canal system

Polder-30: Subpoldering and Community based Water Management

Considerations for Sub-polderization: Land level Canal system Tidal characteristics

of the peripheral rivers

Polder-30: Subpoldering and Community based Water Management

Considerations for Sub-polderization: Land level Canal system Tidal characteristics

of the peripheral rivers

Road network

Polder-30: Subpoldering and Community based Water Management

Considerations for Sub-polderization: Land level Canal system Tidal characteristics

of the peripheral rivers

Road network

Polder-30: Subpoldering and Community based Water Management

Sub-polder

Benefits of Sub-polderization: Better water management, i.e., drainage and flushing of

irrigation water Conflict management between high and low land Involvement of local community in water management Easy and timely maintenance over the years for sub-

polders High depth of water in aman field reduce production; thus

proper drainage will enhance crop yield

Sub-polder 7 NosCommunity base water management Unit/ Block 15 Nos

Level (mPWD) Area below %

0.60 151.00 611.20 801.60 951.80 982.00 99

Digital Elevation Model

Average water level 1.0 m

Lower-Shalta river0 10 20 30 40 50 60

0 20 40 60 80 100

0

0.5

1

1.5

2

2.5

3

3.5

4

Area (sqkm)La

nd le

vel (

mPW

D)

Area (Percent)

Area-Elevation curve

Polder-30: Opportunity for Gravity Drainage

Average water level 1.3 m

Kazibacha river

Maximum water level 2.4 m

Minimum water level 0.0 m

0 0.5 1 1.5 2 2.5 3 3.5 40

5

10

15

20

25

30

35

40

45

0

20

40

60

80

100

Area Elevation curve (Polder 43/2F)

Elevation (mPWD)

Area

(Sq

Km)

Area

(Per

cent

)

Level (mPWD) Area below (%) 1.0 91.2 231.4 521.8 922.0 98

Kharif-1 Kharif-2 RabiAvg WL 1.00m PWD Avg WL 1.20m PWD Avg WL 0.80m PWD

Tidal window 4 hr above 1.40 mPWD: More than 50% area can be irrigated

Polder-43/2F: Opportunity for Gravity Irrigation

Polder-3: Water Management (Drainage and Flushing)

Polder-3: Water Management (Drainage and Flushing)

Land use has changed over the years Shrimp culture has been introduced Huge number (133 pipes and 27 private regulators)

of informal structures have been built for flushing brackish water into the polder

Present drainage system needs to be revisited to meet the demand of flushing brackish water

18 new formal structures and improved canal system can meet the demand of flushing brackish water

Benefits: If properly managed, brackish

water can be considered as a resource, can be used for high-income aquaculture without jeopardizing ‘aman’ rice

Opportunity for crop diversification

Polder-3: Water Management (Drainage and Flushing)

Assessment of risk of polders for cyclonic storm surge

19 Severe Cyclone Track ( 1960-2009)

Embankment damage during Cyclone SIDR

Assessment of risk of polders for cyclonic storm surge

Assessment of risk of polders for cyclonic storm surge

Assessment of risk of polders for cyclonic storm surge

Polder No: 43/2f

Assessment of risk of polders for cyclonic storm surge

Key Messages

There is abundant fresh water for irrigation in much of Barisal Division throughout the dry season. The water will remain suitable for irrigation all over the year in the changing climate in 2030.

In polder-30, 3.54 million cubic meters of water can be stored in the drainage canals, if re-excavated, and an additional 2400 acres area can be brought under irrigation in the last two months of ‘boro’ season. Storage of freshwater in improved internal drainage canals can meet irrigation demand of boro rice for 20% area of cultivable land in Polder-30

In high saline areas, brackish water can be considered as a resource that, if properly managed, can be used for high-income aquaculture.

In polder-3, existing huge number of informal pipes (133 Nos) and structures (27 Nos) can be replaced by a smaller number of formal structures (18) and improved canal system and existing formal regulators. These structures can be used for both drainage and flushing

Adequate Transboundary flow is required for ensuring flow availability at present and future

Closure Plan

Way Forward to the Project Closure:

Land-use change projections in the study area

Outscaling of the research results:

Workshop presentation in coordination with G5

Institution based workshop: with BWDB, LGED, DAE ,BADCand DoF

Policy brief on drainage management and water availability in present and future scenario

55

Thanks for kind attentionThanks for kind attention