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Impact of Sea Level Rise on Coastal Polders in Bangladesh

Mollah Md. Awlad Hossain
Center for Environmental and Geographic Information Services (CEGIS),

Ahmadul Hassan
Center for Environmental and Geographic Information Services (CEGIS),

Abstract/ Executive Summary:

Sea Level Rise due to Global Warming is scientifically established. Bangladesh is in the frontline to face the impacts of Sea Level Rise. Most of the coastal zone of Bangladesh lies below five meter above Sea Level. With a little rise of sea level a great portion will be subjected to additional inundation. There are about 123 polders along in coastal zone of Bangladesh. The embankment height was estimated using historic Sea Water Levels with return period of 20, 30 or 50 Years. The Sea Level Rise due to global warming was not understood during the design period of Coastal Polders. This rise will have negative effects on functionality of Poldering. Some polder will be overtopped causing massive damage to inside resources, others will be subjected to slow drainage causing problems in cropping period, communication disruption etc. Proper adjustment in polder structures is to be made from the beginning to address these issues in polder design and maintenance system.

Keywords: Sea Level Rise, Coastal Polders, Drainage, Salinity, Embankment, Sluice, Regulator

Location:

Start Date:

End Date:

Program Area: Socio-economic and Policy

Non-commodity: Impact

Objectives:

To understand the impact of sea level rise, in a study by CEGIS, mathematical modelling was carried with support from IWM for assessing the change in water system in river and relevant infrastructures.

Methodology:

According to the IPCC 3 report the Sea Level Rise (SLR) along the coast of Bangladesh will be 14 cm in year 2030, 32 cm in year 2050 and 88 cm in year 2100. To understand the impact of sea level rise, in a study by CEGIS, mathematical modelling was carried with support from IWM for assessing the change in water system in river and relevant infrastructures. The study area was three coastal district in southwest zone of Bangladesh; Khulna, Bagerhat and Satkhira. In the model the water level time series data along the Southwest Rivers were generated using the 2D Model. Then different sea level rise scenarios (14 cm, 32 cm, 88 cm SLRs) have been added to this water level to get the downstream boundary for the one dimensional (1D) Southwest model. In this model the downstream boundary was taken from 2D Bay of Bengal model. The south boundary of the 2D Model was located in the deep sea and has been generated from the predicted tide at Baruva in India and Shearle Point in Myanmar. The upstream boundary was taken from observed time series data. The base year, year 2000, was selected considering average flow in upstream of the Gorai River. The model runs estimated water levels and salinity at specified river nodes distributed over the complex messy river system for years 2000, 2030, 2050 and yr 2100. IMPACT OF SLR ON POLDERS The study area contains thirty five polders covering an area of approximately 4,760 km2, which is about 47% of the total of the three districts considered under the study. These polders are protected by about 2,060 km of barriers either by embankments or natural elevated area with intent to protect the inside resources from floods and tidal surges. Hundreds of numbers of sluice/regulators have been constructed on these embankments primarily for draining the rainwater and secondly to obstruct the seawater from entering into these poldered areas. In base condition, i.e Yr 2000 with no SLR, the flooding area of three districts has been estimated from the Mike 11 model results in rivers and polders using GIS spatial techniques. The flooded areas are categorized in depth classes as: dry, 0-30cm, 30-90 cm, 90-180 cm, 180-300 cm and greater than 300 cm keeping similarities with the widely practiced land classes: F0 (dry to 30 cm), F1, F2, F3 and F4 in Bangladesh.

Source of Information: International Conference on Water & Flood Management (ICWFM-2007), 12 - 14 March 2007, BUET, Dhaka, Bangladesh

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The SLR will have substantial impact on flooding and drainage in terms of land class and drainage duration. These will cause adverse effect with different degree on different livelihoods in coastal zone, specially inside the polders, due to changed flooding and prolonged drainage as primary cause. The consideration of sea level rise as continuous process should be included in planning and design process of coastal polders to minimize these effects.

Knowledge Management: Report/Proceedings