The answer is simple.It is due to open space encroachment and the flow of water obstructed by narrowing down existing gutters and nallas. There is also frequent obstruction and blockages due to wide encroachments by builders, shopkeepers, slum dwellers etc. Other major problem is due to high official corruption in work carrying out by BMC contractor and most of the times, work completion just remain in paper only.
Instead of addressing this problem by widening and deepening the existing gutters and removing the blockages and obstruction and encroachments over the gutters, the citizen of Mumbai compelled to face the flood frequently.
When there is a flood, govt., BMC and media come out with statistics and numbers of high rain, high tide and other things without addressing the root cause. The construction activities in Mumbai reached at many fold for the last 10 years.
For last 15 years, many open space meant for garden, open ground etc. encroached by builders in connivance with officials and politician. BMC using the drainage system which is made by Britishers. Even though BMC collecting huge amount of taxes, the basic infrastructure like improving water and underground drainage system not done.
The simple logic can better understand why Mumbai facing flash flood. Earlier Mumbai nallas and gutters have a carrying capacity of 5 billion litres, now it is reduced to below 3 billion litres. The actual carrying capacity should be increased to 8 billion capacity by increasing the width and depth of all small and big nallas. Just concentrating on Mithi river not going to solve the whole problem.
Thus the flow of water decreased drastically and started overflowing and come back where there is a high tide. For this, govt. and BMC come with statistical data and blame the tax payers for all the problems, while greedy builders and encroachers continue to do their illegal encroachments. Now BMC opened control room, purchased many things, but who gets actual benefit. Again tax payers lost crores of rupees.
Other strategy is to compel residents of old buildings to redevelop their property by benefiting largely to politician-builder-official-criminal nexus.
State Govt. and BMC taking interest in spending money in other areas. If there is a flood, again the state and BMC get central assistance for their failure of duties and negligence, which happened on 26th July, 2005. This is the best example how the non-performance is rewarded and politician and officials and builders benefited.
Let us all hope that State govt, NGO, BMC, Central Agencies or Media make a survey in every area of Mumbai and submit a detailed report for further action. Is it a hopeless hope. I think concerned official and politician not ‘invent’ new excuses and try to address the problem on the ground.