what is the reason for flooding due to monsoon in India?

In Indian cities, 24% of slums are located along nallahs and drains, which overflows during the monsoons. About 40% of the slums have the entire area as well as their approach road completely water logged during the monsoon, thus making it difficult for thoroughfare and trade. Barring waterlogging problems, lives in Indian slums have improved. About 85% of 49,000 slums experienced improvements in facilities such as roads, water supply and electricity over the past five years. Such facilities were available to only 75% of slums in the country when last survey was done in 2002.

So I think poor waste disposal system and unauthorised constructions are the main reasons for the problem. Many of the cities are stocking natural drains for land development projects, thus leading to the overflow of water and sewage onto the low-lying areas and the slums.

For every ill,slum dwellers are blamed.The case is reversed.The pre monsoon maintenance and checks are lacking seriousness. There is no planning,no deployement of staff for repair and it exposes their hollowness of their claims of every thing organised even in  initial showers.The Mumabai deluged in the year 2006 for incompetence of BMC rather than slumdwellers.

Lack of draining capacity. Haphazard Drainage system growth adding on without proper planning

Obstructing this natural flow of water and not accounting for it by creating alternatives creates these problems

POLITICS ALLOWS THE DEVELOPING UNAUTHORISED  SLUMS FOR THE WANT OF THEIR VOTE BANK. IF THE NORMS OR RULES FRAMED ARE STRICTLY IMPLMENTED BY THE AUTHORITIES NOT CONSIDERING THE POLITICAL PRESSURE .MAJOR PROBLEM WILL BE SORETED OUT.