Periodicity of early flash floods in haor areas

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Flash floods are a yearly phenomenon in the haor regions. But the rushing waters inundate the six haor districts usually in late April. This year the calamitous visitation has occurred early April. Is this now becoming a pattern? There is a strong reason to suspect that a change in the rainfall, most likely induced by climate change, in Cherrapunji may have shortened the periodicity of five-six years gap of flash floods in the haor area. In 2017, Cherrapunji, known for the world's heaviest rainfall, recorded 5.5 times more rainfall between March 28 and April 4 than it did during the same period a year earlier. Its natural consequence was the worst ever flash floods the districts of Netrokona, Sunamganj, Sylhet, Moulvi Bazar, Habiganj and Kishoreganj experienced. Not only did it wreak havoc with standing boro crops but also caused extensive damage to poultry, fisheries and livestock in the area.  

The year 2019 again saw another spate of flash floods in the haor region. Although it was not as devastating as it had been in 2017, many farmers suffered the worst with the only crop destroyed by the floods. In 2017, the total loss was estimated at Tk 130 billion (13,000 crore). How much will the crop loss be worth this time? This year also the rainfall quite early in the upper riparian region of Meghalaya has been heavy. The rivers flowing through the districts have their origin in Meghalaya and Assam with about 60 per cent of catchment area draining the haor region. 

Reportedly, waters from a few areas have started receding this time but in other areas the problem is turning grave. This might be due to unplanned flood protection dams with a few of those built rather indifferently. Most importantly, regular monitoring and supervision of repair works are missing. Or else, how can those in charge advance such flimsy excuses as the digging of holes by rats? The dams gave in to onrushing flood waters at several points and shifting the blame on rats is ludicrous. After the 2017 and 2019 flash floods, the vulnerability of dams was exposed and also highlighted what has to be done to protect the mono crop of the haor region. 

There should be a thorough investigation to find out if there was deliberate negligence on the part of those in charge of the dams. If so, the responsible must be meted out exemplary punishment. Several newspapers carried reports months ago on inattention and total neglect to get the embankments or dams in a state of readiness in time but no one cared.  

Apart from dams, the recurring problem also calls for further study on the geomorphology of the area vis-à-vis of the upper reaches that discharge the excess waters beyond the capacity of their catchment areas. One problem, experts find, is the siltation of the riverbeds. Water-carrying capacity of the rivers is fast depleting not only because of siltation but also because of the shrinkage of the width of the rivers. Suffice it to say that the Jadukata River near India-Bangladesh border has drastically shrunk from 168 metre in 2004 to just 68 metre in 2017. Also the Meghna, which receives waters from the haor region, at Bhairab Bazar has both shrunk and silted up. Thus disposal of water from the haors is no longer as fast as it was before. 

So, it is necessary to evict encroachers who have constructed illegal structures on river banks and at the same time carry out capital dredging in order to augment water-carrying capacity of the rivers in the region, including at the bottlenecks of the Meghna. If this is done, the mighty river might drain out the excessive water from the haor area promptly to deposit it to the Bay of Bengal. However, if the periodicity reduces on account of climate change and sea level rises, this may not address the problem. In that case, crops that can be harvested a week or two earlier have to be introduced to the haor area for cultivation.  

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