Bangladesh’s geography includes the extensive river deltas formed by major rivers like the Ganges and Brahmaputra, alongside a network of hundreds of small rivers. The monsoon season, occurring from June to September, contributes to 70-80% of the annual rainfall, while the dry winter months last from December to February. The annual rainfall distribution varies regionally, with the west receiving around 1,500 mm and the northeast and southeast receiving about 3,000 mm.
Despite being a country with numerous waterways and adequate rainfall, Bangladesh, unusually, faces severe water-related problems in different parts of the country due to low natural recharge and high water demand. The use of surface water has been in decline due to groundwater depletion and dependence on groundwater on the rise. The problem of managing groundwater in the drought-prone northwestern Barind tract is severe, where rainfall is low.
Currently, groundwater is vital for life and livelihoods, serving as the main source of clean drinking water and supporting agriculture. Approximately 90% of groundwater withdrawal is for agricultural use.
In densely populated regions, the demand for groundwater often exceeds the natural recharge rates, leading to a continual decline in water levels, a situation referred to as depletion.
This brings significant challenges, including dry wells, increased pumping costs, and reduced water availability for urban areas and agriculture. The situation intensifies food insecurity and water shortages, particularly as climate change results in more frequent droughts and altered rainfall patterns.
Against this backdrop, addressing groundwater depletion is critical. One strategy for mitigation involves using groundwater within safe yield limits, while another approach includes the artificial replenishment of groundwater aquifers.
In the Barind region, the Barind Integrated Area Development Project officially started in 1985 under the Bangladesh Agricultural Development Corporation. It was created to revitalize the impoverished by combating severe seasonal droughts, severe water scarcity, and the need for food security.
The project was reconstituted and upgraded into the Barind Multipurpose Development Authority in 1992. Groundwater issues were not mitigated and attention was given to the surface water bodies. However, groundwater problems need to be mitigated since 78% of BMDA projects rely on groundwater.
Coastal regions of Bangladesh suffer from severe salinity intrusion, exacerbated by sea-level rise and reduced river flow, rendering water unfit for consumption and agriculture, alongside arsenic and bacterial contamination, leading to health crises.
The managed aquifer recharge (MAR) technique is proposed as a practical solution to these groundwater issues across various regions of Bangladesh. MAR is a strategic approach aimed at intentionally replenishing aquifers with water for subsequent retrieval or enhancement of environmental conditions.
This method supplements natural groundwater recharge by either injecting or infiltrating water into the ground. Various techniques are employed in MAR, including the use of infiltration ponds, injection wells, and riverbank filtration.
Groundwater depletion is a significant issue in the Barind area, where the rate of decline ranges from 0.75 to 1.25 feet per year. This is exacerbated by limited natural aquifer recharge and high irrigation demands, leading to the ineffectiveness of some suction pumps.
To address depletion, two primary strategies are suggested: Utilizing groundwater within safe yield limits, which requires considerable time for aquifer recovery, and enhancing groundwater recharge through artificial recharge mechanisms.
Artificial recharge also offers additional benefits, such as mitigating salinity issues in coastal areas and managing water storage in urban centers like Dhaka. However, the disadvantages of MAR projects should also be taken into consideration before implementation.
Implementing a MAR project necessitates a conceptual understanding of aquifer characteristics, such as the presence and type of top aquitard (clay or silt), aquitard and aquifer thickness, hydraulic conductivity, transmissivity, and specific yield.
Properly designing a recharge well and assigning a recharge rate is critical; designing pumping and recharge wells involve different considerations. A low recharge rate is safer but prolongs the aquifer's recharge time, while a high rate risks clogging the aquifer, which occurs when pores are blocked, preventing adequate water flow if the rate exceeds hydraulic conductivity.
Therefore, careful site specific design of recharge rates and well spacing is essential. The success of a MAR project fully depends on appropriate site specific design of the project.
Water quality is also a significant concern, particularly if contaminated water is used, as it can detrimentally damage aquifers. The preferred water sources rank as follows: 1) rainwater (low contaminated), 2) pond and lake water (moderately contaminated), and 3) river water, which in Bangladesh is compromised by urban pollution.
Studies indicate river water quality varies from fair to marginal, with high levels of sulphate and contamination risks like arsenic and salinity. Thus, river water must be treated to remove contaminants before it can be safely injected into the aquifer.
Dr. Mohammad Abul Fazal is a specialist in agricultural engineering. He achieved his PhD in groundwater management from Kyoto University, Japan.