Study reveals 100 rivers, 15pc farmlands already affected; 18 coastal districts in jeopardy
As fresh water flow has tapered off on the upper stream of rivers over the last four decades, due to human intervention mainly in neighbouring India, salinity has intruded into 100 rivers and affected 15 percent of the country’s total cropland in the south-western coastal districts.
This was revealed in a study, Soil Salinity Map, by Soil Resource and Development Institute (SRDI) based on data from 2009.
The coastal region had always been saline naturally and now it has become even worse. Back in 1973, as much as 0.83 million hectares of land was saline. The area has now increased to 1.05 million hectares in 93 upazilas, which makes up more than half the coastal land mass in the Ganges floodplain.
Salinity, said the study, has put the health, livelihood and food security of millions of people in 18 coastal districts in jeopardy.
Experts faulted the death of the Garai due to periodic stoppage of water supply by India’s Farakka barrage for decades, leading to receding groundwater level, extensive shrimp farming and sea level rise triggered by global warming.
Records of Bangladesh Water Development Board (BWDB) show that the water level of the Passur river has increased by 5.6 mm between 1977 and 2009 at Hiron Point of the Sundarbans. Experts attributed this rise to an intrusion by salt water, weakening the flow of fresh water.
The salt water was gradually intruding into the rivers and affecting over 6,200 hectares of farmland (equivalent to 7,140 football fields) on an average annually, the study found.
Published last year, the salinity map was prepared after analysing 2,500 soil and water samples, collected in April-May, 2009 from the entire coast of the country stretching 720 kilometres.
Water in all the rivers in the country’s southwest (in the Ganges flood plain) was extremely saline. The salt water had intruded over 100-km on the Madhumati river in Gopalganj during the summer and it was advancing at a rate of one kilometre a year, pointed out the report.
The salinity level in some areas was as high as 25 ppt (means 25 grams of salt dissolved in one kg of soil or water) where probably no crops will grow throughout the year. At some other points, the salinity was moderate and mild.
“The situation in Satkhira is the worst as the mouths of the two distributaries of the Ganges — the Mathabhanga and the Jalangi — have been totally filled up and Satkhira doesn’t get any fresh water supply from upstream basins,” leading hydrologist Prof Ainun Nishat told The Daily Star.
“Salinity in other districts would reduce if the government builds a barrage across the Ganges and supplies fresh water to the Garai and Madhumati. But I don’t see any hope for Satkhira,” he added.
To prevent salinity, the government had dredged some silted rivers, including the Garai, Kabadak, and Mukteshawari, in the south-western region. But it did not help improve the situation due to lack of fresh water flow in these rivers which could carry the sediments and push back the sea water.
Shrimp cultivation has become very popular in the area since the 1960s. Flooding with high saline water in the area every year was causing higher soil salinity, mentioned the report.
Experts also blamed depletion in groundwater level for the expansion of salinity problem.
“If the groundwater level drops, water from the sea intrudes on the groundwater system, which is happening in the southern districts,” said Iftekharul Islam, a groundwater expert now working as national consultant (environmental safeguard) at the agriculture ministry.
Regarding the study, Khorshed Alam of SRDI said, “The soil and water samples were collected before cyclone Aila hit the area. We believe the salinity level has increased further in the mean time. So we plan to make a new map to help farmers choose suitable crops considering the level of salinity.”
DEATH OF GARAI
The death of the Garai river system is one of the major reasons for salinity in the region.
Since the Farakka Barrage was launched in 1973 on the Ganges river, India had shut down all the sluice gates of the barrage in September to retain water for its irrigation for several months. Across the border, as there had been no water flow for several months, silt filled up the river Garai at the confluence of the Padma near Kushtia over the years.
Consequently, the Garai became totally disconnected from the Padma and was unable to pump in fresh water to the south-western districts down below.
After India and Bangladesh reached the Ganges treaty in 1996, India started supplying minimum of 27,400 cusec of water in the dry season. By then, the Garai became so disconnected that this water could not feed the Garai-Madhumati-Pashur river system.
“The Garai river, which used to supply fresh water to a large portion of the southern districts and the Sundarbans, is absolutely dead now due to the Farakka barrage,” said eminent hydrologist M Inamul Haque.
Dredging the Garai mouth would not help much due to extensive siltation, he added.
But if the Ganges barrage is built to retain water during the rainy season, it could ensure water flow through the Garai-Madhumati and thereby reduce the salinity level in the Khulna-Jessore area, suggested experts.
During the lean period, the country used to get 4,000 cusecs of water daily before the Farakka was built. The amount now has declined to around 2,700 cusecs.
Source: The Daily Star