In three maps, understand how Chennai's natural water system works

Deciphering the Chennai floods in three maps and an overview
news Chennai Floods Friday, December 04, 2015 - 20:01

Have you been trying to reach a loved one desperately for the past three days? Have you been trying to find out the level of water inside and outside the houses of your family members in Chennai?

If you are one of those, these maps will be most useful. These maps give you a sense of the following:

Which are the areas that will see severe water logging when water from water bodies like Adyar River, Cooum or Chembarambakkam Lake overflows?

Which parts of Chennai have the potential of flooding and need to be avoided?

Which are the relatively safe areas that you could move to when rain starts pounding?

These maps have been put together by Sashikumar N of HydroInfotech Solutions, Bengaluru.

They have been designed from data available in the public domain from remote sensing satellites of NASA.

Are they the most scientific and accurate? Well, they might not be, because the data for these maps have been collated from what NASA has made available completely in the public domain. But do they give a fairly comprehensive picture of what Chennai’s flood potential looks like – YES.

How to decipher these maps?

Map 1: Charts out the elevation levels of various areas of Chennai.

Pale blue: The lowest areas when compared to sea level. They have the highest potential for flooding,

Purple: Slightly higher elevation than the blue ones, which means they are still under a risk of flooding.

Green: Higher than the purple or the blue patches, which lowers the potential for flooding.

It is not rocket science to know that water flows from an elevated area to a low lying area. Which means all rain from the green areas is flowing to the blue or purple areas.

When the rivers like Adayar and Cooum or lakes like Chembarambakkam or Porur overflow, the blue and purple areas are worst hit.

These are the areas that need to be prioritized for evacuation and preparation. And evidently, in the current catastrophe, most of these zones have been worst hit.

Map 2: Shows streams in Chennai that are likely to overflow if blocked with construction of buildings.

Look for the thin blue lines all across the maps. The lines might look thin but try obstructing the water flow with a building, and you will see the disaster these streams can cause.

Map 3: The extent of rainfall recorded in various districts of Tamil Nadu that shows the extent of rainfall from Nov 22 to Dec 1.

This throws open a little-known fact -  Pondicherry, Maduranthakam and other districts received more rainfall than Chennai.

Dark red: Highest rainfall

Orange: Heavy to very heavy rainfall

Yellow: Heavy rainfall

The scale in the map will guide you to the amount of rain recorded in each district. 

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