Thread by @rajbhagatt

#Thread
Many parts of #Chennai have been inundated after heavy rains (22 cm) last night. The city like all other in India faces a wide range of issues and it is UNLIKELY to solve any of the urban flooding related problems that it faces within the next 10 years.
Here's why
1/n

Chennai Metropolitan region (in particular the city corporation) is relatively flat terrain and is very close to sea level. The agricultural activity in the region had prompted construction of thousands of lakes which were shallow and large in area

Over the years, the city expanded and in many places (like South Chennai marked here) expanded in low lying areas (and wetlands) which are extremely close to sea level and water would tend to stagnate
Map shows builtup expansion

Even after multiple incidents of floods, flood plains of rivers like Adyar and getting converted into urban area for residential, commercial, industrial uses. It would be impossible to vacate many of these houses

Some of the areas near Adyar river that were flooded in 2020 are shown in this map based on satellite data

Natural waterbodies and wetlands like Pallikaranai which could act as buffer are also being converted by governments (union, state, local) leaving water to go nowhere

Already existing builtup area have also fast densified over the years which means less water penetrates into ground as well.

Since there is no green infrastructure to help the city, one would expect artifical infrastructure to step up. However the street designs, the storm water drain designs (and construction of the same) are in really bad shape that they dont help the city at all

The artificial lakes which once served the agricultural lands could have been repurposed & engineered to act as buffers. However some of them have been lost or contain sewage with reduced capacity or that they are not engineered to act as buffers. Map shows loss of velachery lake

Neither the city's master plan nor does the city's disaster management plan address these issues in a scientific manner. The city disaster mgmt plan (2017) has some SOPs however post no scientific explanation, detailed action plans (location specific) & there is no roadmap either

But the urban flooding is not just in tech details of flood or management of it but is caused by governance. With unelected officials (unaccountable to local public), it is impossible to get people's concerns addressed. For 6 years, the city had no mayor or councillors

Revamping street designs, scientific storm water drain plans/design & execution could cost crores & many years to be on ground even if we start today

Without Municipal Governance reforms, it is not going to work and that would take few years of convincing ,drafting, &execution

This is why I believe that Chennai flooding issue wont be solved in 10 years

But I also hope that a long term road map is drafted (atleast now) for the city so that in 10 years, the city could be relatively safe and liveable..

Thanks to @AnushWeather for that video that showed the status of storm water drains

Few more visuals of the situation: