The cross-rubber dam built at Bhujpur in Chittagong two years ago to facilitate irrigation has caused seawater to get into the Halda river, sharply increasing salinity in the country's lone natural spawning ground for freshwater carps.
Production of fish egg in the river dropped by 60 percent last year to 624 kg from 1,559 kg in 2012 mainly due to the rise in salinity, and experts fear it will fall further this year, dealing a heavy blow to the entire fisheries sector.
“Fish egg production has fallen significantly following the increase in salinity in the Halda. If this situation persists, no freshwater fish will survive in the river,” said Prof Manjurul Kibria, president of Halda River Bachao Andolon, a citizens' platform to protect the river.
With the dam retaining water up to 16 feet deep in the reservoir, flow of water from upstream of Halda decreased, allowing seawater to enter the river.
Salinity in the Halda went up to 2,000 parts per million (ppm) in January against the normal level of 650 to 1,000 ppm, according to officials at Chittagong Water Supply and Sewerage Authority.
The Local Government and Engineering Department (LGED) constructed the 4.5 metre-high dam in 2012 at a cost of around Tk 10 crore without conducting any environmental impact study.
Carp fishes spawn in the Halda from where fishermen collect eggs, and then keep those in small ponds on the riverbank for 18 hours. Once fish fry are hatched, they send those to different parts of the country.
The increase of salinity in the river now threatens the livelihood of several thousand fishermen and egg collectors.
Moreover, around a five-kilometre stretch of the river next to the dam remains dry for around three months from January.
Though the dam was built to facilitate irrigation for Boro and IRRI cultivation on 10,000 acres of land in Bhujpur, Paindong and Narayanhat unions of Fatikchhari, three tea estates -- Achhiya, Halda valley and Khoiyachhari -- draw water from its reservoir for plantation through a three-km-long pipeline.
The LGED is building a similar dam downstream of the Bhujpur dam at the mouth of Harualjuri feeder canal. The dam scheduled to be inaugurated on May 6 will reduce water flow further and worsen the situation.
“If they build more dams, it will harm us further. Last year, egg production dropped significantly. Only God knows what will happen this year,” said Kamal Uddin Saodagar, an egg collector from Gorduara in Hathazari.
Halda Bachao Andolon has demanded that the government refrain from building dams on tributaries of the river or canals linked to it.
The 81-km-long river that originates from Badnatali Hill Ranges in Ramghar upazila of Khagrachhari flows through Fatikchhari, Hathazari, Rauzan and Chittagong Sadar. At Kalurghat, it meets with the Karnaphuli river which empties into the Bay of Bengal.
Asked whether the LGED carried out an environmental impact assessment (EIA) before building the dam, Project Director Khalifa Md Abul Kalam Azad said, “Yes, we conducted an EIA before implementing the project.”
But consulting firm Bets Consulting Service Ltd, which conducted the study on the LGED project, said it carried out a feasibility study on the rubber dam, not any environmental impact assessment.
“Our focus was on the structural strength of the dam, not on its environmental impact,” said Aftab Alam Ansary, a consultant of the firm.
Interestingly, the firm was asked to carry out the study in November 2012, around eight months after the dam went into operation in March.
“The dam was already built when we were asked to conduct the study.” The firm completed the study in January last year, Aftab said.
Asked about it, the project director said they had conducted a study before building the dam, and later asked Bets Consulting Service Ltd to do another study on the project.
In reply to a query why a five-kilometre stretch next to the dam remains dry, Kalam said the river shrinks to a narrow stream during this period of the year.
The government has formed a committee headed by Anisur Rahman, joint secretary at the Fisheries and Livestock Department, to conduct an assessment survey on the Halda river, he said.
It would not take more than a year to complete the assessment, according to Kalam.
He said they might not need to retain water up to 16 feet deep in the reservoir, and could bring it down to 12 feet.