The Bhasan Char is a near shore island in the Bay of Bengal located in the western side of Sandwip and it is separated from Sandwip Island by a 6-km wide shallow channel. It is 60 km away from the mainland of Noakhali District (Fig. 1). The name of this newly emerged island (since 2003) was Thengar Char. Our Honorable Prime Minister Sheikh Hasina introduced the name of the island as Bhasan Char for the relocation of the forcefully displaced people of Rohingya Community of Myanmar sheltered at Kutupalong area of Teknaf in Cox's Bazar.

Geologically, Bangladesh is formed of the recent alluvial sediments (age: from 10,000 years to date) with few isolated Pleistocene terraces (age: from 10,000 years to 2.5 million years) that include Madhupur Tract in the central part, Barind Tract in the northwestern part and Lamai Hills in the eastern part of the country and the Tertiary (age: 2.5 million to 23 million years) eastern folded belts. The folded belts are composed of sandstone, siltstone, and shale/claystone. When these sedimentary rocks encountered at shallow depth below the alluvial sediments, we termed these rock layers as bedrock due to their high rock strength. The western most fold of the easter hill ranges is the Sitakund Anticlinal Structure. The convex part of the fold is called Anticline and the concave part of the fold is called syncline. The Sandwip Channel is a syncline in the western part of the Sitakund Anticline. The Sandwip Island including Bhasan Char is a part of a buried Anticline. Therefore, basement of Sandwip and Bhasan Char Island is strong due to the presence of bedrocks at shallow depth. The land area of the island is increasing day and day since its emergence in 2003 due to the accretion of sediments around the island from the Bay of Bengal.

Bhasan Char was a virgin island before the Rohingya relocation. Bangladesh Navy have implemented a project to develop the infrastructures in the Bhasan Char for the relocation of Rohingya people. Now, all types of urban facilities area available in this island. Various preventive measure has been taken to protect the island as well its inhabitants.

To protect the bank erosion and inundation of the island from tidal waves and surges, three layers engineering protective measures have taken in the island (Fig. 2). The outer layer of the protective measures is the wave breakers. The second protective measure is low height embankment of gravels and geo-bags. Then, the natural mangrove forest and the inner last protective measure is the nine feet height embankment consisting of compacted and consolidated silt and clayey silt taken from nearby sites. The height of the embankment to be raised up to nineteen feet in future keeping the slope ratio at 1:5 with 25 feet top width, which will use as road. Pavement of cement-concrete (CC) blocks will be placed on the outer slope, and planting and grassing will be done along the embankment to protect the erosion of the embankment from tidal surges and torrential rainfall of monsoon time. The embankment is constructed following standard procedure based the model prepared for 100 years return period of tidal storm surges.

The infrastructures of the relocation area is in the northwestern part of the island covering almost one-third area of the island. The embankment is 12.1 km long around the relocation area. There are 120 clusters of houses and for each cluster of houses there is one cyclone shelter, i.e., 120 cyclone shelters. The shelter buildings are designed and constructed using deep foundation to resist against wind speed of 260 km. In the compound of the shelter area, there are schools, hospitals, warehouses to store food for one lac people to supply for three months during any disaster. There are sewage line and waste management system to dispose household waste properly.

For each cluster houses, there is a freshwater pond for household uses. Although the island is surrounded by the seawater (saline water) in the Bay of Bengal, it is interesting that there is a good freshwater aquifer (source) at shallow depth. The quality of the fresh water is in the drinking water standard of Bangladesh, whereas in most of the coastal areas and islands of Bangladesh, enough drinking water is not available.

The tidal surges created by the 2019 Bulbul, 2020 Amphan, and 2021 Yaas Cyclones caused severe damage to the embankments in the coastal islands and areas of Bangladesh, but the Bhasan Char Island was untouched during tidal surges of these cyclones. The main reason of the damage of the embankments is due to poor and weak construction of the embankments and their low heights to resist against tidal surge. If the embankment can be constructed like the embankment of the Bhasan Char following the science and engineering, most of the damage can be reduced in coastal area of Bangladesh. The cyclone shelters of these coastal areas should also be constructed following the cyclone model of 100 years return period as it has been done in also of Bhasan Char.

The people of Bhasan Char were not anxious like the people of other coastal islands and areas, because of their strong embankment and shelter buildings. The rest of the island is covered by the natural mangrove forest that also protect to reduce the wind speed of the cyclone. Therefore, Bhasan Char is an excellent example for a safe, sustainable, and resilient place for forcefully displaced people of the Rohingya community of Myanmar. It was possible for the strong aspiration of the visionary leader and Champion of the Earth, the Honorable Prime Minister Sheikh Hasina.

Professor Dr. M. Zillur Rahman, Department of Disaster Science and Management, University of Dhaka. E-mail: zillur@du.ac.bd