The government needs to make sure that the scanty reserve of fresh groundwater along the coastal districts is not overexploited for agriculture so that it could help resolve the drinking water crisis the people of those areas have long been facing, experts say.
"This freshwater in the coastal region must be preserved to meet the demand for safe drinking water. It should not be used for irrigation or commercial purposes, as the aquifers take a century or even centuries to be recharged with fresh water," said hydro-geologists Anwar Zahid.
Zahid, deputy director (ground water hydrology) of Bangladesh Water Development Board (BWDB), was the deputy project director of a study project, ‘Establishment of Monitoring Network and Mathematical Model Study to Assess Salinity Intrusion in Groundwater in the Coastal Area of Bangladesh due to Climate Change Project.
After the three-year study on the groundwater aquifers at different depths along 19 southern districts of the country, BWDB researchers have come to a conclusion about the existence of freshwater aquifers within 800-1,000 feet below the surface in 18 districts, but groundwater aquifers at lesser depths in those districts were found to be affected by salinity intrusion.
Directorate of Ground Water Hydrology under the BWDB implemented the project with financial support from Bangladesh Climate Change Trust Fund of the Ministry of Environment and Forests.
The project covered 19 coastal districts, including Bagerhat, Barguna, Barisal, Bhola, Chandpur, Chittagong, Cox's Bazar, Feni, Gopalganj, Jessore, Jhalakati, Khulna, Lakshmipur, Narail, Noakhali, Pirojpur, Satkhira and Shariatpur, having a total of 140 upazilas.
According to the research findings, freshwater was traced within 800-1,000 feet depth in all of the districts, except Satkhira, while Gopalganj, Pirojpur and some parts of Barguna districts had freshwater under 1,100 feet.
Anwar Zahid said saline water intruded till 600-700 feet under soil in the districts where people are suffering from lack of fresh drinking water.
"Our findings have brought a new hope for the people of the costal region, as they can now source the water by setting up deep tube-wells following BWDB model," he said.
He, however, said: "We’ve searched for water till 1,300 feet under the ground at many places in Satkhira, but no fresh water was found. People there have to store rainwater over the year for drinking."
The study indicates the prevalence of high or extreme salinity (over 6,000 micro-siemens per cintimetre) in shallow aquifers (150-210 feet deep) of Khulna, Jessore, Barisal, Jhalakati, Pirojpur, Bhola, Noakhali and southern parts of Barguna and Bagerhat.
Shallow aquifers in some parts of Chittagong, Feni, Chandpur, Gopalganj, Patuakhali are also containing moderately high saline (2,000-6,000 ms/c) water.
The preliminary results of tests also found out low (about 2,000 ms/c) or moderately high saline water in the 2nd or the main aquifers (210-750 feet) in only a few places in Chittagong, Feni and Jhalakati, whereas the aquifers in the rest of the southern districts are containing high or extreme saline water.
The third or the deep aquifers (750-1150 feet) in Bhola, Patuakhali, Jhalakati, Pirojpur, Shariatpur were found out to be containing moderately high saline water, whereas the aquifers in Barguna is containing extreme saline water, showed the primary assessment of the study.
There are also sporadic pockets of both fresh and acutely saline water reservoirs across the region, said officials.
“During the study we’ve considered a diverse range of factors related to physical and hydraulic properties - subsurface sediment, water level, conductivity, permeability, transmissivity, storage co-efficient, and so on,” Anwar Zahid pointed out.
“We’re now receiving the data through an extensive monitoring network, established under the study project funded by the government Climate Change Trust Fund,” he pointed out.
“The diverse range of data gathered from our monitoring network can also be used to formulate a mathematical model for assessing the current rate of irrigation pumping as well as the rate of the rainwater recharges at different layers,” he added.
Another mathematical model developed by Zahid back in 2004 also reveals that it takes about 3-1,100 years for the intrusion of rainwater at shallow aquifers, while it takes about 110-4,400 years for the recharge at deeper ones.
Zahid stressed that the impact of changes at geological scale such as the sea level rise involves the passing away of hundreds of years, but the impact of human intervention in modern times are affecting the environment much quicker.
“We need to assess our resources well to ensure a sustainable use of those, if otherwise, the overexploitation will affect us much quicker than the natural course of changes in the climate can hit us,” he observed.
Asked about the possibility of expanding the groundwater extraction for agricultural expansion in the south, as it is aspired in the draft Master Plan for Agricultural Development in the Southern Region of Bangladesh (2012-2021), Zahid said, “I can’t be sweepingly say irrigation pumping will affect the salinity intrusion in the groundwater, but I must say the limit of the sustainable use be found out and maintained before the expansion.”
Former director general of Water Resource and Planning Organization (Warpo) M Inamul Huq told that agricultural expansion in southern region should focus more on the use of rainwater than on groundwater extraction.
“The first thing you need to do in south is to contain the shrimp farming that has been leading to the invasion of brackish water there. If the shrimp farming is contained, there is enough rainfall there to allow us to expand agriculture. Unfortunately, I’ve learned from media reports that the master plan aims at boosting the shrimp farming in the south,” he said.
According to the 15-year Sector Development Plan (fiscal years 2011-2025) of the Water Supply and Sanitation Sector in Bangladesh, “The development (abstraction) of the deep aquifer is constrained by the threat of migrating arsenic and salinity, and locally constrained by boron, iron and manganese.”
The Sector Development Plan (SDP) also expressed concern over the water quality in shallow aquifers. It includes, “However, at the sub-regional level, it is noted that recharge could be a constraint along the western border of Bangladesh…”
The SDP says until 2025, 9 percent of the shallow groundwater reserve in the country is required for drinking and other human uses, while 12 and 79 percents are needed for environment and agriculture respectively.
Experts stress judicious use of fresh groundwater