Framework for solution to flood situation in eastern Bangladesh

A vast area of the eastern districts in Bangladesh is experiencing severe flooding that extends from Maulvibazar and Habiganj in the north to Brahmanbaria-Cumilla-Feni in the south.  Each of these locations belongs to a different catchment or watershed area. 

Maulvibazar is located within the Manu river catchment area, while Habiganj is situated on the bank of Khowai river.  On the other hand, Brahmanbaria is a part of the Titas river catchment, while Cumilla is a part of the Gomati river catchment area.  All of the above locations eventually drain into the lower Meghna River watershed. 

The parts of Feni that are severely affected by the flooding, namely Parshuram-Fulgazi-Chhagalnaiya upazilas, belong to the Muhuri-Kahua river catchment area.  The Muhuri-Kahua river drains directly into the Bay of Bengal to the south.

Each river, small or big, has a catchment area district that drains rainwater to that river as surface run-off.  Generally speaking, rainfall in one catchment area does not affect the surface run-off and flooding in another catchment area.  During a major flooding neighboring catchment areas merge to form a large flood affected area. 

Most of these rivers mentioned above (Manu, Khowai, Gomati, and Muhuri) are transboundary rivers, which originate in different eastern states of India. There exists no water-sharing treaty on any of these rivers.  India unilaterally controls the flow in each of these rivers through various diversion and water retention projects. 

One of such projects is Dumboor Dam on upper reaches of the Gomati river. It has been reported that the Indian authority opened all sluicegates of the Dumboor Dam to release water from this large retention reservoir, aggravating the flooding situation in parts of Bangladesh. India denies the allegation.  The area of the Dumboor Dam is over 57 sq km and it has a 30-metre tall dam to retain water for generation of electricity. 

News report in Tripura mentioned a total of 347 mm of rainfall over the last few days. The rain is likely to continue for another few days.  This rainfall alone is capable of generating about 20 million cubic meters of water in the dam.  Releasing this amount of water within a short period of time can cause a rise in water flow in the Gumati river, which can aggravate the flooding situation in the Gumati river catchment area along its path. 

The Gumati river flows through various towns and population centers in Tripura state of India for 120 km before it enters in Bangladesh about 5 km east of Cumilla city, which belongs to the Gumati river catchment area.  Although Cumilla city has experienced flooding but it is not the worst affected areas. 

Besides, the effect of flooding from the release of Dumboor Dam likely to have dissipated along the flow in the Gumati river and floodplains along the river within Tripura.  However, it is not an acceptable behavior by an upstream neighbor to release a dam without first consulting the consequences with downstream riparian country. 

India claims that they have flow data collected at three gaging stations along the Gumati river at Amarpur and Sonamura.  It is expected that Indian authority will release the rainfall data along with the river flow data for the Gumati river for the entire duration of the flood event.  They should release similar data for other transboundary rivers, including the Haora, Muhuri, Manu, and Khowai rivers as well.

 The worst affected areas are Parshuram, Sonagazi, Fulgazi, and Chhagalnaiya upazilas in Feni district.  All of these locations belong to the Muhuri and Kahua river catchment areas – not in the Gumati river catchment area, on which the Dumboor Dam is located. 

It is unlikely that the release of water from the Dumboor Dam aggravated the flooding situation in Feni district. For waters from the Dumboor Dam to reach the catchment area of the Muhuri river they would have to cross about 20 km across mountainous areas between Natun Bazar and Jalaibari to the south in Tripura state of India. The straight-line distance between Dumboor Dam and Feni is about 67 km. Besides, the Gumati river flows to the west from Natun Bazar towards Melaghar in Tripura.

The question that begs answer is what is the cause of such devastating flooding in eastern parts of Bangladesh in general and in Feni in particular?  Firstly, the amount of rainfall, timing and duration of rainfall are directly attributed to surface run-off and flooding.  For instance, the average annual rainfall in the Indian state of Tripura is 2,200 mm with an average 60 per cent (1320 mm) during the monsoon season that occurs between June and September. 

As per the news report by Daily Deshkatha in Tripura, the amount of rainfall on 21 August was 145 mm, which is a daily record.  The amount of rainfall during the last two days (20 and 21 August) was more than 327 mm, which is 25 per cent of monsoonal rain.

Similar rain pattern was also observed in eastern districts in Bangladesh.  The rain is predicted to continue for a few more days. At this rate, the carrying capacity of rivers is overwhelmed, resulting in floods.  The intensity and duration of torrential rainfall have increased over the last few years due to climate change. 

Secondly, the water carrying capacity of rivers has declined over the years due to siltation of riverbeds caused by agriculture, hill cutting, deforestation, and unplanned urbanization practices.  Urbanisation of a catchment area results in an increase in impervious areas that are conducive to additional run-off from rainfall.  It is worth noting that the intensity of flooding is more severe in urbanised areas, such as Parshuram, Fulgazi, Chhagalnaiya, and Khagrachari. 

This is due to the decline in natural drainage network in urban areas where most of the natural canals and rivers are grabbed by encroachers and the storm drains are clogged by illegal dumping.  Thirdly, flood water cannot be discharged efficiently by rivers in low-lying areas due to the rise in sea level during the last few decades.  The Muhuri river drains to the Bay of Bengal via the Feni river.  The discharge of flood water is further delayed due to tidal cycle near the coast. 

What can be done to resolve the flooding problem?  Unfortunately, there is no easy solutions, but there are ways in which the flooding and waterlogging in urban areas can be reduced to acceptable level.  First, all the natural drainage network needs to be recovered from encroachers and be cleared of obstruction to flow by dredging. 

Second, the original size of the drainage network will have to be increased to accommodate additional surface run-off that results from urbanization and climate change induced extra rainfall.  Third, the efficiency and carrying capacity of storm drains will have to be adjusted in line with watershed slope and the degree of urbanization. 

Fourth, adaptation measures need to be taken in designing houses and infrastructures that can withstand the flooding that is likely to increase in the future.  Fifth, an integrated water and sediment management plan needs to be formulated for all transboundary rivers in light of the UN Convention for Non-navigational Water Courses (1997).

Sixth, the flood warning system and disaster management protocol will have to be modernized to keep pace with the changing reality of climate change and unplanned urbanization that we have created.

*Md Khalequzzaman, professor of Geology, Commonwealth University of Pennsylvania, Lock Haven, PA 17745; mkhalequ@commonwealthu.edu