Md Khalequzzaman is an internationally renowned geologist who writes extensively on climate change and its geological impact. He teaches geology and physics at the Lock Haven University, USA. He spoke to The Business Standard during his recent visit in Dhaka.
When we talk about Bengal Delta or the Gangetic Delta, what is the area we refer to?
It is a huge area which covers almost 80 percent of the landmass of Bangladesh. It's the Gangetic delta which is a flood plain as well. A big part of it is an active delta. When a big long winding river carries a huge amount of silt and flows down to the sea, its current is slowed down causing the silts to stratify as sediments. When a huge amount of silt sediments at the mouth of a river, we call it a delta. We are the second-largest delta in the world, next to Amazon. The southwest part of Bangladesh falls under the area of the active delta.
Our southwest region ends at Sathkhira. Does the active delta end there?
No. It continues to India. The Sundarbans area in West Bengal is a part of this landmass. It extends as far west as Medinipur. In the north, it extends to the southern banks of Padma. In the south, this active delta continues as far as the bottom of the sea. This silt forms a kind of a fan in the sea bed, which we call Bengal fan. It's a subaqueous delta.
And is it an inevitable reality that this huge delta is sinking?
Every delta in the world has a tendency to sink. We are yet to determine the exact rate of its subsidence. But I bet, it's not the fastest. Mississippi delta in the USA has the fastest sinking rate now. Moreover, not all the areas in this Bengal Gangetic Delta is sinking at the same rate. There are numerous factors involved.
Why should we consider the subsidence rate? Why is it crucial?
Where there is subsidence, the level of the land will tend to go down. This is simple arithmetic. And there is another grand reality – the sea level rise which will double the effect. The polder embankments we are erecting may not suffer the effect in a short span of time. But given a time span of, say, four or five decades, the effect will be strikingly visible. The area inside the polders, as a result, will start facing water-logging. We should take account of the reality of delta subsidence when we design our projects in the southern areas. The Delta Plan we have formulated has taken account of the subsidence, I am told.
You often mention the decrease of silt in the rivers. Given the situation, what can we do?
We need to increase our understanding of the field-level reality. We need to determine the exact amount of silt each river is carrying. We need to know the fate of the silt, for instance, where it is being sedimented – whether it is being sedimented in rivers beds or it's going to the sea. We need to have field-based studies. We can't go far with guesswork. We need to know the detailed geological story that is unfolding here. Moreover, we have to work out plans to make the best use of whatever amount of the silt we have. In the USA, the silt sediments of Mississippi river is pumped and distributed in wider areas. We can do the same. We can distribute the silt in areas where sedimentation is low.
Climate change is a phenomenon that is unfolding all over the world. Do you think the Bengal Delta has anything unique about it? Do we face bigger threats than others?
Yes, ours is a very unique and special situation. First of all, unlike any other, we have a very densely populated area, especially in the coastal belts. Take the case of the Netherlands, which is often cited as a success story for protecting their land area.
They have a significantly lesser population density than we do. We have a completely different dynamics of siltation and rainfall. There is heavy rainfall in a narrow corridor of rainy season. It results in a completely different pattern of river flow. Because of these unique dynamics, we are more vulnerable to sea-level rise and increase of cyclonic storms.
It is predicted that by 2,100 sea level will rise by two meters. What would it be like to live in such a reality?
It will not be an end-of-the-story-scenario altogether. A two-meter rise of sea-level will not inundate 40 percent of the landmass right away. As the sea-level increases, siltation will happen at the same time which we often fail to count. It will not be a bath-tub effect where you open up a faucet and the tub starts to sink. The deltaic land will not sink following that manner. Siltation will negate this sea-level rise. We need to manipulate this sedimentation in such a way that we can mitigate the effects of sea level rise. But a two-meter rise will indeed bring about huge impact.
Can our existing embankments hold?
A recent study by the Center for Environmental and Geographic Information Services (CEGIS) has revealed that the majority of embankments, more than 50 percent of them, cannot hold an 88-centimetre rise in sea level. We can all predict what a two-meter rise will mean. It is clear that polder embankments are not a long term solution. We need to consider new ecological approaches. We have to learn to build new kind of homes that can sustain adverse situations. We need to invent new crops that are salt tolerant. We need to embark on numerous research initiatives.