Water Development Board officials said erosion has taken place at different points in the dyke's 17 kilometre area from Meghai in Kazipur upazila to Shimla in Sadar upazila.
They said three spars of the dyke – Meghai spar numbers 2 and 3 and Shimla spar number 2 -- might become ineffective anytime due to the high velocity of water and formation of whirlpools.
Board officials said 10 spars were built between Singrabari in Kazipur upazila and Shuvogachha in Sadar upazila at a cost of Tk 95 crore during the previous Awami League government to check the Jamuna erosion and divert the river course.
But most of the spars have been ineffective, as the board was reluctant to maintain them during the successive four-party alliance government, they said adding that the Shoilabari 'groyn', spanning around one kilometre, has been engulfed by the river.
The officials said the board sought an allocation of Tk 27 crore from the government early this year for repairing and rehabilitation of the spars, but have yet to receive any fund.
Sirajganj Water Development Board executive engineer Sujoy Chakma, however, said they have taken prompt measures to repair the Meghai spars.