Significance of embankments to protect tidal floods

The coastal embankments currently play a vital role in protecting the region from climatic events, boosting agricultural outputs, improving livelihoods of the coastal people, and coping with climate change impacts

Bangladesh is a low-lying delta, making it one of the most vulnerable countries to climate change. The coastal region adjoining the Bay of Bengal is characterized by a vast network of morphologically active tidal rivers. The strength of the tides and the flatness of the delta causes the tides to influence river process a long way upstream in the southern estuaries. And climate change has intensified the tides in recent years. Bangladesh has major floods every year which engulf about 33 per cent of the country. During the last few decades, under the programme of flood control and drainage improvement, about 7,555 km of embankment (including coastal embankments of about 4,000 km), 7,907 hydraulic structures including sluices, and around one thousand river regulators, 1,082 river closures and 3,204 km of drainage channels have been built spending a thousand crore Taka. Under the scheme a total of 332 projects, aimed at freeing 3.5 million ha of land from flood water, have been implemented. Thus, about 24 per cent of the total land area and 39 per cent of the net cultivated area have been protected. However, in this programme some form of natural detention basin, channel improvements, flow diversions and bank stabilization and anti-erosive measures have been tried. Other than the flood control embankments on the floodplains, the railway and national road embankments constructed during the colonial period played a major role in flood mitigation. The Coastal Embankment Project (CEP) covers the coastal districts of Bangladesh and includes Cox's Bazar, Chittagong, Feni, Noakhali, Laxmipur, Bhola, Barisal, Patuakhali, Jhalokathi, Barguna, Pirojpur, Khulna, Satkhira and Bagerhat districts. The CEP comprises a complex network of dikes and drainage sluices and was the first comprehensive plan for providing protection against flood and saline water intrusion in the coastal area. The project was implemented between 1961 and 1978 by the Bangladesh Water Development Board in Phase - I comprise some 92 polders providing protection to one million hectares of land. Phase - II consists of 16 polders covering another 0.40 million ha. Polder is a Dutch word meaning an area enclosed by dikes. Within the CEP more than 4,000 km of embankment and 1,039 drainage sluices have been constructed. Embankments include sea dikes at locations facing the Bay of Bengal, wide rivers and at places where high waves occur; interior dikes along rivers where wave action is less severe; and marginal dikes are along channels where current and wave action is mild.

These embankments are intended to protect land from tidal inundation but cannot prevent overtopping and damage from cyclonic surges and tidal bores. In addition to increased agricultural production, these embankments have provided good road communication and contributed towards improvement of the overall socio-economic condition in the coastal zone. Embankments have also been constructed as integral part of large irrigation projects. For example, in Chandpur irrigation project there is a 100 km embankment along the Meghna and Dakatia  rivers, 65 km in the Meghna-Dhonagoda Irrigation Project along the Meghna, 50 km along the MANU and KUSHIYARA rivers in the Manu river project, and 80 km along the Teesta river in the Teesta Barrage Project.
The coastal embankments currently play a vital role in protecting the region from climatic events, boosting agricultural outputs, improving livelihoods of the coastal people, and coping with climate change impacts. But the arable lands located within the polders are only slightly higher than sea level. Without embankments, the coastal communities will be subject to tidal fluctuations. But a huge amount of money is needed to redesign and repair the coastal polders. According to the BWDB, about two billion dollars is required to fortify the coastal embankments to withstand natural disasters, including cyclone and storm surge, due to climate change.
Impact of Embankments: i. Limitation of flooding to a known area of land. ii. Reduced risk of flooding elsewhere. iii. Relatively low cost of construction and maintenance. iv. Durability of flood banks compared to frequent in-stream engineering work. v. Floodplain area can be used for much of the year, and may provide a useful buffer zone, helping prevent pollution of watercourses by agro-chemicals or farm wastes used in nearby arable operations. Nutrient deposition in the form of river-borne sediments will help keep the area which floods fertile. vi. Opportunity to create valuable additional wildlife habitat, e.g. species-rich grassland or riparian woodland. vii. Potential financial support/encouragement from agri-environment schemes. viii. Drawbacks of setback embankments. viii. Reduction in productivity of land within the flood banks. ix. Restriction on intensity and type of farming activity that can be undertaken within flood banks. x. Setback flood banks may be difficult for individual landowners to adopt effectively, as it is best applied over long stretches of riverside land on both sides of the river.
Since 2013, with World Bank funding and expertise, Bangladesh has provided improved protection to 183,900 people including 91,950 women with increased resilience to climate change.
Challenge: Bangladesh’s coastal zone spans over 580 km and includes territory where 28 per cent of the population resides. A higher percentage of the population lives below the absolute poverty line in the coastal area than in the rest of the country. A World Bank study on the cost of adapting to extreme weather estimated that eight million people are currently vulnerable to inundation depths greater than three meters due to cyclonic storm surges. This number will increase to 13.5 million people by 2050, and an additional nine million because of climate change. There is an urgent need to rehabilitate and upgrade protection polders – areas of low-lying land - and enhance the resilience of coastal areas to cyclones, tidal and flood inundations, and salinity intrusion.
Approach: The Coastal Embankment Improvement Project (CEIP) was designed to support the rehabilitation and upgrading of protection polders to protect the coastal areas from tidal flooding and frequent storm surges and improve agricultural production by reducing saline water intrusion in selected polders using climate data and climate projections. The long-term objective of CEIP is to increase the resilience of the entire coastal population to tidal flooding and disasters by upgrading the whole embankment system. With an existing 6,000 km of embankments with 139 polders, the magnitude of such a project is enormous, necessitating a multi-phased approach to be adopted over a period of 15 to 20 years. CEIP-I is the first phase of this long-term programme. Furthermore, the project will create a framework for polder design and investment plan, based on understanding of the long term and large-scale dynamics of the delta.
Results: Since 2013, the $400 million Coastal Embankment Improvement Project (CEIP), has helped Bangladesh mitigate some of the large impacts of cyclones and flooding and improve emergency response in the coastal region. The project has increased protection of 183,900 people including 91,950 women with increased resilience to climate change in selected polders from tidal flooding and storm surges. As of May 2019, the project has protected 21,700 ha of gross area and upgraded 130.58 km of embankment. A comprehensive analysis is being undertaken to better understand the coastal dynamics to increase climate resilience in the coastal area.

The writer is Consultant, Community Development Centre (CODEC), Chattogram, Bangladesh.

 

Significance of embankments to protect tidal floods

The coastal embankments currently play a vital role in protecting the region from climatic events, boosting agricultural outputs, improving livelihoods of the coastal people, and coping with climate change impacts

Bangladesh is a low-lying delta, making it one of the most vulnerable countries to climate change. The coastal region adjoining the Bay of Bengal is characterized by a vast network of morphologically active tidal rivers. The strength of the tides and the flatness of the delta causes the tides to influence river process a long way upstream in the southern estuaries. And climate change has intensified the tides in recent years. Bangladesh has major floods every year which engulf about 33 per cent of the country. During the last few decades, under the programme of flood control and drainage improvement, about 7,555 km of embankment (including coastal embankments of about 4,000 km), 7,907 hydraulic structures including sluices, and around one thousand river regulators, 1,082 river closures and 3,204 km of drainage channels have been built spending a thousand crore Taka. Under the scheme a total of 332 projects, aimed at freeing 3.5 million ha of land from flood water, have been implemented. Thus, about 24 per cent of the total land area and 39 per cent of the net cultivated area have been protected. However, in this programme some form of natural detention basin, channel improvements, flow diversions and bank stabilization and anti-erosive measures have been tried. Other than the flood control embankments on the floodplains, the railway and national road embankments constructed during the colonial period played a major role in flood mitigation. The Coastal Embankment Project (CEP) covers the coastal districts of Bangladesh and includes Coxs Bazar, Chittagong, Feni, Noakhali, Laxmipur, Bhola, Barisal, Patuakhali, Jhalokathi, Barguna, Pirojpur, Khulna, Satkhira and Bagerhat districts. The CEP comprises a complex network of dikes and drainage sluices and was the first comprehensive plan for providing protection against flood and saline water intrusion in the coastal area. The project was implemented between 1961 and 1978 by the Bangladesh Water Development Board in Phase - I comprise some 92 polders providing protection to one million hectares of land. Phase - II consists of 16 polders covering another 0.40 million ha. Polder is a Dutch word meaning an area enclosed by dikes. Within the CEP more than 4,000 km of embankment and 1,039 drainage sluices have been constructed. Embankments include sea dikes at locations facing the Bay of Bengal, wide rivers and at places where high waves occur; interior dikes along rivers where wave action is less severe; and marginal dikes are along channels where current and wave action is mild. These embankments are intended to protect land from tidal inundation but cannot prevent overtopping and damage from cyclonic surges and tidal bores. In addition to increased agricultural production, these embankments have provided good road communication and contributed towards improvement of the overall socio-economic condition in the coastal zone. Embankments have also been constructed as integral part of large irrigation projects. For example, in Chandpur irrigation project there is a 100 km embankment along the Meghna and Dakatia rivers, 65 km in the Meghna-Dhonagoda Irrigation Project along the Meghna, 50 km along the MANU and KUSHIYARA rivers in the Manu river project, and 80 km along the Teesta river in the Teesta Barrage Project. The coastal embankments currently play a vital role in protecting the region from climatic events, boosting agricultural outputs, improving livelihoods of the coastal people, and coping with climate change impacts. But the arable lands located within the polders are only slightly higher than sea level. Without embankments, the coastal communities will be subject to tidal fluctuations. But a huge amount of money is needed to redesign and repair the coastal polders. According to the BWDB, about two billion dollars is required to fortify the coastal embankments to withstand natural disasters, including cyclone and storm surge, due to climate change. Impact of Embankments: i. Limitation of flooding to a known area of land. ii. Reduced risk of flooding elsewhere. iii. Relatively low cost of construction and maintenance. iv. Durability of flood banks compared to frequent in-stream engineering work. v. Floodplain area can be used for much of the year, and may provide a useful buffer zone, helping prevent pollution of watercourses by agro-chemicals or farm wastes used in nearby arable operations. Nutrient deposition in the form of river-borne sediments will help keep the area which floods fertile. vi. Opportunity to create valuable additional wildlife habitat, e.g. species-rich grassland or riparian woodland. vii. Potential financial support/encouragement from agri-environment schemes. viii. Drawbacks of setback embankments. viii. Reduction in productivity of land within the flood banks. ix. Restriction on intensity and type of farming activity that can be undertaken within flood banks. x. Setback flood banks may be difficult for individual landowners to adopt effectively, as it is best applied over long stretches of riverside land on both sides of the river. Since 2013, with World Bank funding and expertise, Bangladesh has provided improved protection to 183,900 people including 91,950 women with increased resilience to climate change. Challenge: Bangladeshs coastal zone spans over 580 km and includes territory where 28 per cent of the population resides. A higher percentage of the population lives below the absolute poverty line in the coastal area than in the rest of the country. A World Bank study on the cost of adapting to extreme weather estimated that eight million people are currently vulnerable to inundation depths greater than three meters due to cyclonic storm surges. This number will increase to 13.5 million people by 2050, and an additional nine million because of climate change. There is an urgent need to rehabilitate and upgrade protection polders areas of low-lying land - and enhance the resilience of coastal areas to cyclones, tidal and flood inundations, and salinity intrusion. Approach: The Coastal Embankment Improvement Project (CEIP) was designed to support the rehabilitation and upgrading of protection polders to protect the coastal areas from tidal flooding and frequent storm surges and improve agricultural production by reducing saline water intrusion in selected polders using climate data and climate projections. The long-term objective of CEIP is to increase the resilience of the entire coastal population to tidal flooding and disasters by upgrading the whole embankment system. With an existing 6,000 km of embankments with 139 polders, the magnitude of such a project is enormous, necessitating a multi-phased approach to be adopted over a period of 15 to 20 years. CEIP-I is the first phase of this long-term programme. Furthermore, the project will create a framework for polder design and investment plan, based on understanding of the long term and large-scale dynamics of the delta. Results: Since 2013, the $400 million Coastal Embankment Improvement Project (CEIP), has helped Bangladesh mitigate some of the large impacts of cyclones and flooding and improve emergency response in the coastal region. The project has increased protection of 183,900 people including 91,950 women with increased resilience to climate change in selected polders from tidal flooding and storm surges. As of May 2019, the project has protected 21,700 ha of gross area and upgraded 130.58 km of embankment. A comprehensive analysis is being undertaken to better understand the coastal dynamics to increase climate resilience in the coastal area. The writer is Consultant, Community Development Centre (CODEC), Chattogram, Bangladesh.