Bank Erosion and mitigation for Meghna, Hatiya and Sandwip Channel

Land Erosion of CDSP developed Chars in Boyerchar, Noler Char, Caring Char, Char Nangulia, Char Maksumul Hakim, Polder 59/3C and Urir Char is vulnerable. In December 2013 the Institute of Water Modelling (IWM) completed their Assessment of Erosion Vulnerability of the East Bank of Meghna River; the study recommended and gave an indication of the stability and rate of erosion of the coast from Jarirdona River in the north along Boyerchar and Noler Char up to Caring Char in the south. As a follow up to the erosion study, and in line with discussions and advice of the 2014 Supervision Mission, TA Project Engineers have installed benchmarks along the coast line of the project for regular monitoring of the erosion. The latest measurement was taken in early March 2024 and it was found that present erosion is still alarming from the location of Chatla khal sluice at Boyerchar to the polder 59/3C through Noler Char and Char Nangulia. In the meantime full Caring Char is engulfed. Two thirds of Noler Char and one third of Char Nangulia is already eroded.

However, the erosion rate at regulator Gabtali in Boyer Char has reduced significantly, but already it is extremely vulnerable and as per IWM survey based 10 years safety line the regulator is extreme outside the alignment and required to be replaced under future CDSP V phase.

Average yearly erosion during the 5 years bridging period at Boyerchar (CDSP III) maximum 92 m near Chatla regulator. Yearly average of maximum Noler Char erosion found 778m near Thanarhat Bazar and that of Char Nangulia erosion is 529m near Karim Bazar Cyclone Shelter. At Char Maksumul Hakim there is erosion as well as accretion; average maximum erosion is 146m close to Eastern embankment. Both Erosion and accretion found at Urir Char, yearly average maximum erosion around 128m at the North West part.

The most likely cause of this severe erosion is the formation of a new char in the Hatya/ Sandwip Channel in front of those Char locations, diverting the river flow towards the bank, The erosion has been accelerated after the bank protection work of Swarna dweep mostly by reflected current.

A revised alignment for construction of a retired embankment was adopted for the Boyerchar, Noler Char and Char Nangulia part for length 27.44km . Further development of the erosion is closely monitored by the project. Since measurement started in July 2019 maximum Cumulative erosion was 433m at Boyerchar close to Chatla khal Regulator, 3678m at Noler Char close to Thanar Hat Bazar, 2495m at Char Nangulia close to Karim Bazar Cyclone Shelter, 676m at Char Maksumum Hakim close to Eastern embankment, 563m at Urir Char close to 4 No khal Ghat.

At Urir Char Accretion is also active at east and west side of the Char. After the construction of Noakhali Urir Char Cross dam, it is forecasted there will be huge accretion at the East, West and North part of Urir Char but erosion rate may be increased along the South.

BWDB has started bank line protective work since last December 2023 for erosion prevention at Noler Char for 4.90km bank line with contract amount Tk3780million. BWDB also submitted DPP to the planning Commission for the protective work at Boyerchar & Char Nangulia with estimated budget amount Tk 8180million and 11070million for the eroding bank line of length 12.00km and 14.00km respectively.