Cyclone and Storm Surge - Iczmpwb.org

3.21
3.15. Kolkata city’s drainage system – a closer look
The physiographical setting of Kolkata is such that the land slopes from the higher banks of the river
Hooghly towards the marshlands of the east that connects to the network of rivers and channels
draining to the Bay of Bengal. In fact, there are pockets in the city that are rather low-lying and water
has to be evacuated from the storm drainage system (underground in most parts of the city proper)
by pumping. It has been observed that there is a general trend of water logging in the regions which
have a north – south alignment of the underground drainage pipes, some of the areas being as
under:
1. Amherst street
2. Thanthania
3. Chitpur
4. Free School street
5. Camac street
6. Sarat Bose Road
The problem is aggravated by the fact that streets and roads occupy just about 6 to 8 percent of the
city area. And for many of the large houses, the roof top or courtyard rainfall water is led to the road
side gutter instead of being directly led to the underground drainage system. The road side gutters
are not always sufficient in size and are often covered with garbage, thus causing blockage of the
water from entering the pipes below.
It must also be reiterated here that the drainage system that still supports the flushing of the storm
water in the Kolkata city proper is based on the original design of William Clarke, with some additions
in the later years, Hence, there has really been not much of augmentation of the original system and,
on the other hand, there has been a steady deterioration of the system by way of sediment
deposition. It is understood that the cross sectional areas of these pipes have been reduced to 30
percent of their capacities, in many stretches. Some details of the pumping system and the open
drainage channels, or khals as they are called in local parlance, is given in the following sections:
3.15.1. Pumping arrangements for the drainage system
The saucer shaped topography of the city of Kolkata has led to the establishment of a number of
pumping stations to flush out the storm water. These are maintained by different agencies, and a list
of some of the important pumping stations is given in Tables 3-6, 3-7 and 3-8.