Low-lying areas in rural Patna and Nalanda were inundated on Thursday after the rising waters of the Falgu and Sakri rivers breached several small dams, officials said.
The two rivers were in spate following heavy rains in neighbouring Jharkhand over the last few days, they said.
Among the affected areas were Pandarak and Fatuha blocks in Patna, and Hilsa block in Nalanda, they added.
"Portions of Baruane Zamindari Dam located on the left bank of Dhanayan river in Pandarak block and Sirpatpur dam got damaged last night because of the discharge of 53,945 cusec of water from Sakri and Falgu rivers from Uderasthan dam causing a flood-like situation in low-lying areas of Pandarak and Fatuha blocks in Patna district," said a statement issued by the Water Resources Department.
"Similarly, two small dams in Hilsa block, which were in a very dilapidated condition, of Nalanda district were damaged causing a flood-like situation in several areas of Jamuar and Dhuri Bigha villages," it said.
No causality was reported, and villagers of the affected areas were being moved to safer places, it added.
Water Resources Minister Vijay Kumar Chaudhary told PTI that the situation was under control.
"Necessary items have already been brought for the immediate repair of the damaged small dams, which were not constructed by the Water Resources Department. Besides, teams of senior WRD officials are already there for immediate repair and rescue measures," he said.
Patna's District Magistrate Chandrashekhar Singh said it was due to the breach of small dams, also known as zamindari dams, which were constructed by local authorities, water entered certain low-lying areas.
"The situation is completely under control and officials concerned took immediate action. Flood control materials such as sandbags and bamboo were taken to the site on boats. The repair work is on," he told PTI.
