Restore river, canals: Experts

The waterlogging in Chittagong city is mostly a man-made situation caused by unplanned urbanisation, destruction of water bodies, canals, drains and natural hills and forests, said experts.

After Monday's flooding that the residents of the port city experienced for the fifth time in the last three months during this monsoon, The Daily Star yesterday spoke with two urban planners regarding the causes of the flooding and the probable remedies. 

They said siltation of the Karnaphuli river and its channels as well as canals connecting it also aggravated the situation.

Major dredging in the Karnaphuli, building navigation gates and water retention reservoirs for the river and excavation of new canals would improve the situation, they advised.

An effective management mechanism needs to be introduced to preserve the existing canals, drains and ponds and natural resources such as the hills and forests, two urban planners told The Daily Star yesterday.

In their opinion, the waterlogging problem would be well addressed if the functionality of these resources is ensured by reclaiming these from encroachers and by protecting these from indiscriminate littering.

Town planner Engineer Subhash Barua, who is also vice president of Forum for Planned Chittagong (a platform advocating development of Chittagong city), said unplanned urbanisation is one of the main reasons for the city's waterlogging. “However, there's not much you can do about it now since thousands of structures have been built in an unplanned way, leaving no room for the accumulated water to disperse during the monsoon.”

“So, all you have to do is make the best effort with your existing opportunities to improve the situation,” he said, adding that all the canals and drains will have to be desilted first to raise their water retention capacity. 

“Hill preservation and hill management are vital aspects in improving the waterlogging situation as drains and canals are silted with soil washed out of hills during the monsoon,” he said.

The hills need to be planted with grass and trees and a drainage network should be built there incorporating silt traps, he added, explaining that the silt traps or small ponds, built on a foothill, would help stop siltation of drains and canals by collecting soil washed out from hilltops.

Both sides of all canals will also need to be freed from obstruction and illegal encroachment so surface water can easily disperse through these. 

Aside from waterlogging during monsoon season, many parts of the city including Agrabad, Halishahar and Bakalia remain flooded almost all year long during high tides in the Bay of Bengal.

Asked how to address this situation, Shahinul Islam Khan, chief town planner of Chittagong Development Authority (CDA), said the riverbed of the Karnaphuli has elevated due to siltation and a comprehensive dredging work is necessary to enhance its water retention capacity. 

Once its capacity is raised, the river will be able to hold the excess water during high tides and thus delay entry of tidal water into connected canals as well as adjoining low-lying areas, he explained.

In the second phase, all ponds and water bodies, especially canals and drains will need to be reclaimed from illegal occupation and water retention capacity of all the canals and drains should be enhanced through excavation and restoration, Shahinul said.

Long-term steps should also be taken so siltation and littering does not clog these up and both sides of the water dispersion channels remain unobstructed, he said, adding that in the third phase, navigation gates and sluice gates should be installed at the mouth of the Karnaphuli to control the flow of water into the canals.

The CDA chief town planner also recommended building of water retention reservoirs at the river mouth.

Meanwhile, Chittagong City Corporation Mayor AJM Nasir Uddin in a press conference on Monday said the CCC had taken a number of projects including excavation of a new canal and a 4,600 foot-long drain and clearing of existing canals and drains from obstruction and siltation.