One of my colleagues from Delhi was once commenting over phone regarding Mumbai rains. He was making fun of the drainage system and water logging and trains being effected during heavy rains. I told him that there were two reasons for it -
One : Mumbai, being on the coastline, experiences more rains than Delhi. And of course, the tides effect it as well.
Two : Most of Mumbai is reclaimed land. And a number of small rivers are silently buried within the city. During heavy rains and high tide, these rivers show their presence / wrath through increased water levels, so that we're reminded constantly of what we've done to them. Mithi river (buried in the Andheri Kurla stretch of land and going upto Dadar) is one such example. It has remained as a gutter or nalla in some places. Everyone dreads the wrath of Mithi (also known as Mahim creek).
My colleague agreed and that's how our conversation ended.
Let us understand that Mumbai as it is now is a united area of seven Islands. Isle of Bombay, Colaba, Old Woman's Island (Little Colaba), Mahim, Mazagaon, Parel, Worli. These Islands alongwith the nearby islands of Trombay and Salsette were merged to form Greater Bombay. A number of small rivers and creeks are thus buried beneath Mumbai and these rise with heavy monsoons and high tides during monsoons.
I'd further like to add here that Mumbai, being the financial capital, is more in the spotlight for any reason from heavy rains to potholes to crowded trains to buses etc. It always rains heavily along the Indian coastline resulting in flooding, rivers overflowing and the like. But in smaller places/ villages, it is never highlighted as an issue. Rains had started in Goa and Konkan region much before it rained in Mumbai. One of our relatives in Goa had called last month to tell us how rains were very heavy this year and many parts had flooded. But I never saw it on National Television. In fact, even with two days of continuous rains there has not been much flooding as previous years except in ex-river zones like Milan subway (this was also supposed to be a bridge over a river/ creek but none is seen there now), saki naka, kurla, mahim etc. Beneath these areas lies the Mithi River and maybe many more small creeks/ rivers. These will continue to show their wrath during monsoons!