Water is a fundamental element with which we work on a daily basis at Amusement Logic, so we are always on the lookout for new things, curiosities and discoveries that are made in any of its aspects. Today we bring you the results of a study on what has come to be known as the “Bengal Water Machine“, recently published in the journal Science of the American Association for the Advancement of Science. The authors of the research are Mohammad Shamsudduha, Richard G. Taylor and Md Izazul Haq of the University College of London (UCL); Sara Nowreen of the Bangladesh University of Engineering and Technology; Anwar Zahid of the Bangladesh Water Development Board; and Kazi Matin Uddin Ahmed of the University of Dhaka, Bangladesh.
The paper published in Science collects results from the analysis of one million groundwater level observations in 465 wells across Bangladesh, collected weekly over 30 years, between 1988 and 2018. As summarised by UCL, the extensive research concludes that the collective pumping of groundwater by some 16 million small-scale rice farmers in Bangladesh “has created vast natural reservoirs underground that rival the world’s largest dams“. At the same time, these large reservoirs support “irrigation that has transformed this previously famine-prone country to a food-secure nation”. Specifically, the study estimates that monsoon rains have deposited between 75 and 90 km3 of water underground in Bangladesh over the past 40 years – twice the capacity of China’s Three Gorges Reservoir.
But what is the process that has transformed much of Bangladesh’s monoculture floodplains into highly productive, even triple-cropped land and made the country the world’s fourth largest rice producer? First, to understand how it came about, we must go back to the early 1990s, between 1992 and 1994, when terrible droughts hit Bangladesh. As a result, a rapidly growing number of rice farmers turned to groundwater to irrigate their fields and therefore started the “water machine”. In the following years, groundwater extraction in the dry season, the inter-annual period between November and April, lowered the water table. So, when the heavy rains of the monsoon season arrived between May and October (when 90% of the country’s rainfall occurs), the water found a wider and deeper layer of soil ready to absorb it. This reduced flooding, on the one hand, while, on the other, the same water was held captive in the unsaturated soil layer and, instead of draining into the Bay of Bengal, flowed down to recharge the aquifers.
As UCL’s Mohammad Shamsudduha explains, “the Bengal Water Machine is a nature-based solution, requiring a comparatively minimal intervention —i.e. shallow irrigation wells that are less than 100 meters below ground level— relative to dams“. However, the system has its limitations. So, according to the same geologist, the recharge rate increased in 153 of the 465 wells (35%) in which they took boreholes, while in the rest “the degree of change was different”. “I was even horrified,” the scientist said, “to see some borehole records because the storage of water in those places is almost zero“. These data highlight that low surface permeability geology can be restrictive for induced aquifer recharge.
According to the study, “alluvial plains in the seasonally humid tropics cover an area of nearly 4 million square kilometres” of the planet. In many of these areas, geology permitting, the sustainable irrigation represented by the Bengal Water Machine could be replicated. This would increase food security and reduce the risk of flooding.
or those of you who speak Bengali (and for those who don’t, the images are interesting enough), we encourage you to find out more through the Bangladeshi Channel 24, with this short documentary:
