How kolkata will be under its own waste ?

The amount of wastewater is increasing due to rapid urbanization in Kolkata, a metro city in Eastern India. Previously a river named Kulti was used for channeling the wastewater to the Bay of Bengal. Now due to increase in the amount of wastewater is increasing and decrease in river width of the River Matla where the River Bidyadhari confluences and River Kulti mixes with River Bidyadhari.If flowing area is decreasing then wastewater can not flow through it. So the wastewater will start to backflow. Then wastewater will submerge area of Kolkata. So literally speaking “Kolkata will be submerged under its own waste”.