The Cyclone Amphan and its impact in the city kolkata
Back ground:
In the present topic, I have tried to highlight the basic areas of concern, which have been severely influenced / affected by the consequence of the Super Cyclone Amphane, particularly in Kolkata. Along with, I have also discussed the concern key points in very brief to understand the sustainability of the city of Kolkata to face the virulence of the Super Cyclonic Amphane , that buffeted the region with strong winds and heavy rains. I feel that these might help to some extent to guide the planner in the future days to apply their mind to evolve a new thought and to fight any such incident conforming with the city’s peculiar character.
Discussion with the relevant issues:
The cyclone Amphane made us awakens about our position to sustain and fight against any similar incident in coming days.
It is true that it has made severe disastrous in the city’s daily life and stalled activity for a few days almost completely.
Nearly total failure was seen in the electric supply line due to uprooted electric posts and other mishap in the distribution system. Loss of electricity, failed to supply the potable water at different localities for a few days. In many areas, the road was under inundation due to water logging. The pumping station cannot be operated smoothly. As a result , it takes additional time to be dried up.
Hundreds of big /small trees fell down on different roads /streets and blocked important road communication. Moreover, foliage and twigs of trees felled by Cyclone Amphan choked a kerbside catch pit in many places on 21st May,20 . As these pits are the receiving points for storm water runoff on road surface , which gets channeled ultimately into the underground drainage system, thus , any obstruction in flowing water , leads to deter the drainage process severely. Therefore, clearance from the plant debris was urgent needs to restore swift drainage in the locality.
Incidentally, it is pertinent to mention here that that the City of Kolkata has some locational advantages, as the ground level along the left bank of river Hooghly in KMC area, remains at higher ground level and the river section can accommodate the upland high discharges and no spill over flow effect was noticed so far in the adjoining Kolkata city .
Thus, the city’s basin area mainly receives the localized storm water run-off which is generated from its own catchment / basin, but no other contribution added from any other sources.
But, the city has other drainage problem due to its unique geographical feature (bowl shaped), for which the gravitational flow does not function at all, in the existing drainage network system . Actually, 83% of the city core area, depends on forced pumping fully, activated through some of the major pumping stations, linked with several intermediate small boosting stations, located at strategic location and low pocket areas. The main pumping stations disposes accumulated drainage water forcefully into higher level of the outfall drainage canals ( SWF Channels) , which runs almost 35 km towards eastward to meet ultimately in Kultigong river , which is of tidal nature for which the drainage flow sufferers at least by 12 hours in a day.
Almost 83 sq km of city core area and 17 sq,km of added KMC area are activated through forced pumping into SWF channel system., Apart that , the drainage water from 21 sq km of core city area, passes through Bagjola khal and river Hooghly directly through sluice gates. (, a small area adjoining Hooghli river)
The SWF channel system including the Bagjola khal runs toward eastward direction due to favourable gradient /slope pattern of the terrain .However, in extreme southern portion of added KMC area ( 66 sqkm) , the drainage is performed through west -bound canals e.g Tolly’s nullah, Monikhal, Churial khal etc ,
In view of above facts, the roll of pumping stations in the city core area , is very important as forced pumping is only the option to drain out water from the city’s existing drainage network.
Therefore, the electric failure in any of the pumping station, if happens, may obviously would obstruct the drainage process, as a result there shall be continuation of water-logging in the concerned sub-basin area and inevitably, the road shall not be dried up easily.
The Cyclone Amphan and its disastrous effects in Sundarban anchal , coastal districts and Kolkata area :
We all aware that the Amphan made landfall near Bakhali in West Bengal at 2:30 p.m. IST on 20 May, buffeting the region with strong winds and heavy rains.
Actually, it was formed on 16th May 20 and reached the peak intensity over the Bay of Bengal on 18th May. Finally, the super cyclonic Amphan strike near Kolkata at 3pm on 20th may
Amphan was a Very Severe Storm with a wind speed of 155–165 kmph. It was the strongest tropical cyclone over Bay of Bengal since the 1999 Odisha cyclone.
West Bengal, the epicentre of the cyclone’s landfall, saw the most widespread damage from Amphan. The storm was considered the strongest to hit the region in over a decade. The Coastal areas in West Bengal including the districts namely East Midnapur, North 24 Parganas, and South 24 Parganas , Howrah , as well as Kolkata Bengal — were affected severely by the cyclone in the state of West Bengal.
The trails of destruction :
In these zone ,there is massive damages of homes and uprooting trees and electric poles. Many people were killed , most of the fatalities were due to electrocution or the collapse of homes.
Moreover, in the Sundarbans areas, innumerable no of breaches occurred in the embankments, led to the flooding of villages and swaths of cropland.
Such inland inflow, extended a long distance in the country side. Many Embankments in the region were overtaken by the surge, leading to inundation of large number of islands in the Sundarbans.
One report says that Saltwater inundation caused massive damages for rice paddies , vegetable and sesame crop .
A high storm surge of 5 m (16 ft) in riverine water , inundated a wide areas , severed coastal communities and communications .Moreover, the Bridges linking islands to the Indian mainland were also swept away. Along with ,innumerable no of homes were destroyed.
Kolkata Region:
In Kolkata, damaging winds up to 133 km/h (83 mph) overturned vehicles and snapped hundreds of trees.
A day after cyclone Amphan wreaked havoc over the city, Kolkata woke up to scenes of destruction i.e on 21st May 2020 . Thousands of trees, hundreds of lampposts and several traffic signals were uprooted with electricity cut off.
As electric poles collapsed, CESC Ltd disconnected power supply in majority of the areas, plunging the city into darkness.
Telephone lines were snapped, broadband services hit and even mobile network was down in most parts of the city kolkata.
The storm also triggered widespread flooding / water-logging around the city due to extremely heavy rainfall.
The areas like College Street, Behala, New Alipore and Sukia Street were submerged with high depth of water . Similarly, other many areas in south, central and north Kolkata, were also badly waterlogged due to such incessant rain fall.
Rain fall & drainage index in Koliata :
It may be mentioned here that in Kolkata the drainage index adopted varies from 75 mm to 150 mm in a day. The northern part of the network (T.H.C. System) which started functioning during 1876 has been designed with a rainfall of 1/4th inch per hour (150 mm per day) with 100% run off and the southern part (Suburban System) established in 1890 or so has been designed to a 1/6th inches rainfall per hour (100 mm per day).
In the seventies, attempts were made to augment the capacity of the system to ½ inch rainfall per hour, but the target could not be achieved due to various technical and financial constraints.
On an average, the city experiences about 4 to 6 water logging in a year. It is reduced after eighties.
Moreover, it is also noticed that the rainfall in a day may exceed 200 mm occasionally.
In the present cyclonic storm, the India Meteorological Department’s weather monitoring station at Alipur in Kolkata recorded exceptionally high rainfall of 236 mm over the last 24 hours from 20th morning to 21st May )morning. Similarly, the Dum Dum area in the city of joy also received 200 mm rainfall, while Salt Lake area witnessed 183 mm on Wednesday.
With the above data from the IMD report , it is amply clear that Kolkata region received more than 200 mm R/F per day . But, on the other hand , the pumping system can cater maximum 150 mm per day or 6 mm per hour. Thus, consequence to the present drainage infrastructures, the city would definitely be suffered from the drainage congestion and keep remained under submersion..
Now ,the question may be raised for its duration and its depth of inundation.
It is felt that the localities which passes over lower ground level , with no boosting pumping station , may likely to have water logging for a depth of around 2ft to 3ft with duration period for 24 hours to 48 hours or so.
However, the situation would depend definitely on the efficacy of concerned pumping stations and its sewer network to drain out storm water for the instant period.
Observation:
Aftermath of Amphan cyclonic storm, we noticed a total imbalance in city life:
i) Electricity was interrupted severely due to fall of electric cable posts.
ii) Huge no of trees was uprooted , halted the existing road communication and electric transmission at many places
iii) Electric current failure caused shutting down of local pumping stations at many places.
iv) Thus, temporary stoppage of electricity caused pausing to water supply and the process of draining in the inundated areas.
Under this scenario, it is felt that the overhead power line could not sustain the virulence destruction of the “storm Amphan” and broke down suddenly and made the city under darkness in a large areas which took a few days for normal restoration . During long outages after the catastrophe, there are considerable direct economic and mental impact to the people with discomfort , anxiety and helpless.
It would be good if the electric supply authority ltd avoids the overhead power transmission system in Kolkata at the maximum possible end , instead of that, executes the underground power cable lines to stop repetition of similar incident in future.
It is also noticed that the existing big trees as planted around the city ,were also the major factors to deteriorate the trailing disastrous effects, aftermath the cyclonic storm. It is revealed that thousands of trees were broken down and uprooted with cracking a large chunk of earth from the base ground, associated with boundary wall and damaging the building structures, in many cases.
Therefore, we may need to be careful in selecting proper trees before any plantation adjoining the city roads . In most crowded cities, the tree which grows big accompanied with large surrounded branches, are usually avoided for the road side plantation to keep away the virulence of future accidents, followed by sudden snapping during the massive wind blowing.
Moreover, the trees should be trimmed in regular manner and make it safe from sudden uprooting from the ground earth, putting at risk in human lives.
Conclusion:
It is a fact that the with the help of latest satellite images , IMD communicated the severity of cyclonic storm to the Kolkata residencies , for which the people tried to stay in house as far possible , otherwise the fatality rate would have been much bigger.
After all, we cannot stop the passage of this unprecedented cyclonic storm and associated extremely heavy rainfall over Kolkata, but we can think a better planning & improved disaster response in time to tackle such great eventualities, particularly, aftermath of such cyclonic disastrous effects.
But, the question arises why the Kolkata suffered for days for electricity failure, stoppage of potable water supply and continuation of water logging in many areas along with the massive disruption in road communication .
Probably, i) lack of regular trimming of tree branches in normal time & ii) want of application of improvised mechanised equipments /machineries etc , prevented for prompt removing the tree /plant debris at places .
This had lead high deterrence to restore the existing communication at the earliest possible time and along with , the presence of twig and foliage at the mouth of the catch pit , could not facilitate an early disposal of drainage water .
Moreover , prior to the effect of cyclonic storm, it was also necessary for iii) an alternative suitable arrangements for temporary installation of emergent portable generator sets by the competitive authority, at the strategic locations in the power cut areas .This could have helped a lot for both temporary emergent supply of potable water and quick drainage from the water logged areas.
It is amply clear, from above that the main source of water-logging in kolkata is the heavy storm water precipitation , which could have been intensified further in the instant case , if it would occur , within 4 to 10 hours instead of scattering in 24 hours in a day . Of course , it depends on the weather pattern .
Moreover, the information of probable vulnerable affected areas with depth of inundation ,conforming to the IMD latest forecast , may have to be brought to the concerned people in time after prior identification each vulnerable areas with its depth of inundation , due to the heavy storm .
Along with , every endeavor also needs to be taken that affected people gets real time response from the NDMA people during the shifting process , if requires , in the prior identified high level safe shelter on emergent basis.
Incidentally, it may be mentioned here that Kolkata remains in better position as it does not has to face the fury of overflowing river i.e either from Hooghli river ( adjoining western side) or kultigong river ( 35 km away towards east ward direction ).
But, on the other hand , during the Amphan storm , the coastal Bengal and sundarban area , had to suffer both i) the storm water run off generated from its own basin area as well as ii) the fury of storm surge that over topped the riverine embankments, inundating a large areas , with saline water in the country side .
This has caused a massive damages to the standing crops and also the loss of land fertility for a couple of years. The affected people , not only lost their houses, but also could not have any high level safe shelter to move in most cases .
