The ‘Bengal Water Machine” has attracted a lot of attention since researchers wrote about it in Science in September. It is the serendipitous result of the Bangladesh government making it easier and more affordable to import diesel-powered pumps so its farmer could make its floodplains much more productive.

“For decades, millions of farmers in Bangladesh have been capturing more water than even the world’s largest dams”, says Science. “They did so simply by irrigating intensively in the summer dry season using water from shallow wells. The ability to use groundwater to irrigate rice paddies during the dry seasons (January to May) helped Bangladesh become food self-sufficient by the 1990s, which was no small feat for one of the most densely populated countries in the world.”

But the farmers had no idea that they were creating a flood control system, says Mohammad Shamsudduha, a geoscientist at University College London who is one of the paper’s authors. It was his research on groundwater dynamics with his supervisor Richard Taylor in 2007 that began to uncover the totally unexpected result. And that, too, was serendipitous.

As farmers pump water from the ground in the dry season, they free up space for water to flood in during the wet season. Thus the pumping turned single-crop, rain-watered land into land that produced double and sometimes triple crops, making Bangladesh the world’s fourth highest producer of rice.

Juggadery/Wikimedia Commons.

Calculating the magnitude of seasonal freshwater underground storage capture in the Bengal Basin over the past 40 years, Shamsudduha et al found that monsoon rainfall has recharged 75 to 90 cubic kilometers of water over that time – a volume equivalent to twice the reservoir capacity of the Three Gorges Dam, Science reported.

The Business Standard called it the ‘miracle in the Delta’. “For years, the prevailing understanding has been that groundwater depletion is a development disaster. But here was a decade-long research finding which flew in the face of existing logic. Dubbed the Bengal Water Machine (BWM), Shamshudduha and his team further found that groundwater harvested for farming over the past 10-20 years was not depleting at the same rate in different regions, taking variables into account.”

That is because the Ganges and the Brahmaputra carry a wealth of silt and sediment from as far away as the Himalayas that gets deposited in the delta, making its soil so fertile. It also creates small pores in the ground, so the heavy rains to soak into the ground for farmers to use, instead of running off to the ocean.

In essence, Bangladesh is like a sponge. During the dry season, it dries out as farmers tap into it. But that gives it more room to absorb more water in the monsoon, creating the self-sustaining cycle they call the Bengal Water Machine which was ‘essentially unknown’ before this paper.. 

“If there was no pumping, then this would not have happened,” says Kazi Matin Uddin Ahmed, a hydrogeologist at the University of Dhaka in Bangladesh, and another of the paper’s authors. 

The researchers think there might be other “water machines” elsewhere in the tropics with similar wet-and-dry climates. Southeast Asia might host a few, at the mouths of the Red River, the Mekong, and the Irrawaddy.

“So far, we have found where the water machines are working. We also got to know how much extra water has been recharged over the last 30 years. It is also known that its level of effectiveness is different from place to place,” Shamsudduha says.

“Now it will be easier to mark places, meaning wherever the water machine works, there is no need to impose restrictions. And where it does not, necessary projects should be undertaken to increase the storage of groundwater or to prevent the water table from going down.”

Sources:

The Bengal Water Machine: Quantified freshwater capture in Bangladesh. Science, Sep. 14, 2022

The “water machine” of Bengal. Science, Sep. 15, 2022

Farmers accidentally created a flood-resistant ‘machine’ across Bangladesh. Popular Science, Sep. 15, 2022

The miracle in the Delta: Bangladeshi scientist who discovered Bengal Water Machine. The Business Standard, Oct. 13, 2022

Featured image: End of Winter. New Plantation. Abhijit Kar Gupta, Kolkata, India. Wikimedia Commons.