Salinity intrusion into the aquifers of the country’s coastal districts has reached an alarming proportion due to unplanned use of groundwater in agriculture and seawater seeping into underground due to sea-level rise caused by global warming.
“We’ve assessed the quality and quantity data of groundwater up to 1,100 feet deep in 19 costal districts. But, we’ve found saline water in aquifers within just 600-700 feet deep,” deputy director (Groundwater Hydrology) at Bangladesh Water Development Board Dr Anwar Zahid told UNB.
He said salinity intrusion has gripped some coastal districts since there is no freshwater layer up to the depth of 1,100 feet.
“There’s no freshwater layer up to 1,100 feet deep in Barguna, Pirojpur, Gopalganj and Satkhira…freshwater may be found 1,300-1,400 feet deep the ground.”
The hydrologist said water layer is found up to only 300 feet deep the aquifer in Satkhira, but the layer is full of saline water.
“If you assess the water after 300 feet deep the aquifer, you’ll find only clay there due to deltaic formation of soil,” he said.
Dr Zahid said people have already been suffering a lot for lack of freshwater in the country’s coastal districts as salinity has reached an alarming proportion in groundwater of the region.
In the coastal areas, drinking water mainly comes from deep tubewells, while irrigation is limited to surface water bodies.
Freshwater is also available at shallow depth sourced from seasonal precipitation but turns brackish during dry season.
There is a high vulnerability to salinisation due to pumping-induced mixing of preexisting fresh and saline groundwater.
Fresh groundwater is also vulnerable to vertical infiltration of saltwater due to periodic storm surge flooding, Dr Zahid said.
Because of its low-lying topography, he said, Bangladesh will be more vulnerable due to climate change impacts in the future.
He said rising sea levels will cause the tidal saltwater wedge to intrude further upstream in rivers, bringing changes in salinity affecting coastal groundwater aquifers.
“Salinity is also increasing gradually in the surface water of the coastal rivers. The agriculture will face trouble due to salinity rise in river water. If freshwater availability decreases in the coastal belt, food grain production will face setback creating food crisis in the country.”
Dr Zahid said in the coastal areas where availability of fresh and safe water is a big problem due to arsenic contamination and saline water intrusion in upper aquifers, assessment of probable impact of sea-level rise on deep freshwater is of utmost important.
He said the government is going to complete a study (January 2011 to December 2013) to assess surface water as well as groundwater resources of two pilot areas of the coastal belt.
Directorate of Ground Water Hydrology, Bangladesh Water Development Board with fund from Bangladesh Climate Change Trust Fund of the Ministry of Environment and Forests is implementing the project titled, ‘Establishment of Monitoring Network and Mathematical Model Study to Assess Salinity Intrusion in Groundwater in the Coastal Area of Bangladesh due to Climate Change’.
The project area covers 19 coastal districts that include 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.
The main objective of the project is to determine different hydro-geologic parameters in coastal groundwater resources in order to assess both the quality and quantity of groundwater highlighting extent and intensity of salinity requiring for irrigation and safe water supply planning, development and management as well as for model development and also assess the impacts of climate change.
About the outcome of the study, Dr Zahid said, “We’ve found limited freshwater in costal aquifer. It should not be used in irrigation.
The freshwater in the coastal region must be preserved to meet the demand for safe drinking water.”
He said a monitoring network has been established and some 600 observation tubewells installed under the project to monitor both groundwater quality (including distribution of salinity) and quantity (measuring water table).
Groundwater users, farmers, planners, policymakers, scientists and researchers will get benefit from the data and analytical results gained from the study and investigation for sustainable development and management of groundwater considering the climate change aspects, he said.
Dr Zahid said the installed tubewells will help strengthen the existing network monitor any change in groundwater recharge and quality as well as saline front movement in the coastal belt.
Model simulations under different hydro-geologic and variable climatic parameters will predict future changes that will provide valuable guideline for planning of water use and agriculture considering changing cropping pattern, he added.