Thread by @TNGeography

Bangalore sits above 2900ft, one have to be master in bad planning to flood a high altitude, rich metro city.

All cities are not made equal, cities like Mumbai & Chennai with their flat terrain, costal tides, heavy rainfall are geographically flood vulnerable.
#bangalorerains

I meant, places like Bangalore, flood mitigation is easier & less trivial/complex. You need to follow gradient, valleys.Higher flow speed meant small drain could evacuate more water, it doesn't stagnate in this terrain. Old Bangalore withstood these rain with avg drain system 1/n

Chennai/Mumbai sit in 5-7m height, water flow very slowly, stagnate more. In these "Mega cities", canal depth cant go above 5m(shallow), otherwise sea water will enter the city. They also receive heavy rainfall. So, flood mitigation is non-trivial and complex plan is required 2/n

Lets compare flood rainfall
1. Yesterday few places in Bangalore received ~130mm, many places got 50-100mm in 24hrs
2. 2015, many places in Chennai got 200-350mm, with peak of 490mm near Tambaram
3. 2005, Mumbai got peak of 950mm rainfall in 24hrs. So, cities need to prepare 3/n

Bangalore need to prepare for peak of 120-200mm. Anything >80mm flood the Bangalore new areas.
Chennai need to prepare for 300mm, Mumbai need to prepare for 400+mm. So, with all the advantage of terrain, mitigating flood in Bangalore should be less complex, straight forward 4/n

Coastal towns like Nagapattinam, Udupi are less commercialized, they can withstand very heavy rainfall, without major flood. Same cannot be said about flat costal mega cities. Mumbai/Chennai need much more attention and plan than Bangalore to mitigate flood 5/n

But New areas of Bangalore were permission was granted by BBMP in every level of construction are shame for a city planner. This canal shown in pic, is on the collecting point for 25% of Bangalore area rainfall, it connects Bellandur with Varthur see what happened to it 6/n,

From here onwards my twitter thread on Bangalore drainage will be added 7/n

https://twitter.com/TNGeography/status/1495798487547772932?s=20&t=wlX1yYZOL3LVqAROkCI8-w

Post about Bellandur lake overflow 8/n

https://twitter.com/TNGeography/status/1566643197820149760?s=20&t=mFIwylxlzcft_LoHOmcTsQ

Post about Arkavathi [arts of west Bangalore 9/n

https://twitter.com/TNGeography/status/1564453587459407874?s=20&t=wlX1yYZOL3LVqAROkCI8-w

Cities on river get flood due to water carried by rivers like Ganga in Patna, Tungabhadra in Kurnool, Ulhas in Mumbai, Yamuna in Delhi, Jhelum in Srinagar but Bangalore is in river basin boundary. So no external water enters city. Need channels just to drain its own rainfall 10/n