Dhaka city has lost a combined length of 120km or 307 hectares of canals, which could have been waterways and vital drainage, thanks to encroachment, unplanned urbanisation and lack of maintenance by the authorities in the last 80 years.

For context, the length of canals lost is more than the distance between the capital and Mymensingh city.

A study by River and Delta Research Centre (RDRC) found that 95 canals have been completely lost or their lengths have been less than halved.

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How can we bring our canals back from the dead?

The researchers compared the 1880-1940 land survey, officially known as the Cadastral Survey, and satellite images of 2022.

According to the 1880-1940 survey, there were 54 major canals, 111 narrow canals, the old channel of the Buriganga, and nine lakes.

Currently, there are 77 major canals, 31 narrow streams and several lakes in the two city corporations. Successive governments excavated 10 major canals and four new lakes in the city over the decades.

The city has the Turag river on the north and northwest, the Buriganga on the south and southwest, and the Balu on the east.

The study titled Atlas of Dhaka's Canals, Channels and Lakes: Mapping Changes says Dhaka has 206km of watercourse, down from 326km mentioned in the Cadastral Survey.

RDRC Chairman Mohammad Azaz said, "The city has been experiencing critical loss of water bodies due to rapid urbanisation and development."

During the Cadastral survey, canals and river channels occupied 565 hectares of land in the city. Fifty-five percent is gone now.

Of the 307 hectares lost, 33.75 percent is occupied by different structures, 18.92 percent farmland, 16.94 percent streets, and the rest have either been filled up or became wetlands with no water flow, says the report.

Buildings were built in places of canals in Mohammadpur, Hazaribagh and Kamrangir Char. Major canals like Dholai Khal and Mohakhali Khal are in poor state because of encroachment.

As the Cadastral survey was conducted in the lean seasons it did not include the foreshore and wetlands. Despite this, Hazaribagh Khal, Katasur Khal, Ramchandrapur Khal, Amaiya Khal, Atir Khal, Bailjuri Khal, Bhaturia Khal, Dhalpur Khal, Dholai Khal, Gobindapur Khal, Gopibagh Khal, Haikkar Khal, Lawtola Khal, Nasirabad-Nandi Para Khal, Rampura Khal and Rayerbazar Khal have each lost around 2 hectares of land.

Begunbari Khal, Ramchandrapur Khal, Dholai Khal and Rampura Khal each are now shorter by over 3 km.

The Buriganga's old channel, currently 4.32km, lost 2.46 km of its length and 18.63 hectares of land. Besides, some rivers have become canals.

Abdullahpur and Katasur canals were connected to the Konai river while Hatirjheel Lake, Begunbari, Rampura and Norai canals were part of the Norai river.

The Dholai river is now a canal known in different areas as Nasirabad, Nandipara, and Dakhsingaon while the Atir river is now the Atir canal due to severe pollution and encroachment, the study says.

Azaz said the government has taken steps to free the Buriganga's old channel, "But no restoration has been done. More participatory and collective efforts are needed to save the waterbodies."

Sharif Jamil, member secretary of environment group Dhoritri Rokhhay Amra, said, "The canals that disappeared were necessary to protect the groundwater table and drainage system of Dhaka. Government officials responsible for protecting the canals did not do their jobs.

"In cases, the land grabbers, officials and politicians in collusion legalised encroachment."

Dhaka District Commissioner's Office is the owner of all the land of the canals. The government recently ordered the two city corporations to maintain 26 canals.

According to a report of the taskforce consisting of the National River Conservation Commission, Dhaka District Administration, Wasa, Department of Environment, and BIWTA, there are no specific authority for the maintenance of 12 canals.

Malik Fida A Khan, a member of the National River Conservation Commission, said, "It is still possible to save the existing canals. The mayors can take steps."

He added that in recent years, canals have disappeared due to lack of water flow caused by garbage dumping. Then someone fills up the land and build structures.