An overview — the drainage aspect of Bidhannagar Municipal Corporation area, Bidhannagar, Kolkata :
o: Introduction :
Bidhannagar Municipal Corporation. Bidhannagar, the most important satellite township of the city of Kolkata is situated on the eastern edge of the city. Bidhannagar, earlier known as Salt Lake (“Laban Hrad”), is started as a planned township built on reclaimed swamp land. Later on an area enriched with wet lands of East Kolkata (a Ramsar Site) was included on the eastern side.
As for its origin, after the partition of Bengal during Indian independence in 1947, a lot of people migrated from Bangladesh, the then East Pakistan, thus rapidly increasing the population of Kolkata and to relieve the city from this huge population pressure, as an alternative solution, on 16 May 1955, Calcutta Gazettee Government notification was published, to acquire 8,760.50 acres (35.4525 km2) of Bheries (pisciculture area) under the Sec1 of Land Acquisition Act, 1884 and subsequently, a master plan of creation of Salt Lake City was approved on 9th April 1964, now known as Bidhan Nagar. The main purpose was to develop a satellite city to the mother city Kolkata due to its adjoining location from Kolkata.
Originally, it was swampy stretch of land on the eastern fringe of Calcutta and a Yugoslav firm was entrusted with the reclamation work of the water-filled area. Five-mile long pipes were laid down from Ghushuri to Salt Lake for sand filling. It took not less than 7 years to fill up the 15 sq. km. of land with sand water, which was a very fertile fishing zone and thus, a water land was converted as a sandy area. Finally, on 16th of April, 1962, the Salt Lake City was born.
Initially, this planned city was under the South Dum Dum Municipality, then it came under the wings of Urban Development Department of West Bengal and subsequently in 1989, Notified Area Authority was set up. Ultimately 1992 onwards, Salt Lake has come under the wings of the Municipality Authority.
On the onset, Sector-I, Sector-II and Sector-III was complete within the period 1965 to 1969, for occupancy. Then came up the Industrial Sectors — — — IV and V. The 12.52 sq. km. area of the dream city initially comprised of 12873 plots of land apart from 87 housing estates and blocks. The land area has almost doubled now with the inclusion of Duttabad, Sukantanagar, Nayapatti and Mahishbathan
o. Some important facts:
The Bidhannagarh city is located 7.5 km far from core area of Kolkata city in eastern side. The aim of this development was to set up a township. Salt Lake is roughly formed as a polygon, in a total area of little more than 13.16 sq.km, and divided into five well organized sectors. The Sectors are further sub-divided in Blocks. Being a planned township, Salt Lake City, has been divided into 25 wards and ninety four blocks, mainly consisting for large apartment complexes. The land surface of Salt Lake City, Kolkata is generally situated on plane land that is known as Indo-Genetics plain.
One report states that out of the total study area (13158467 sq m), which is constant according to previous planning: in 1964 the built-up area is 80212 sq m, in 1973 the built-up land is 542818 sq m, in 2002 its increase to 9677926 sq m, in 2007 the built-up rate is 9592619 and in the year 2012 its increase to 9793462. It means at the beginning the population rate is very low and it suddenly increases after 2002.
This also shows to understand the degree of urban growth in the dynamic of Salt Lake City area in Kolkata.
According to 2001 census the population of Bidahanngar Municipality was 1.68 lakhs. This has been estimated to rise to 2.76 lakhs in 2011 and gradually to 4.72 lakhs in the year 2025. As per report of Census India, population of Bidhannagarh city is 2, 18,323 and density is 15,590 / sq. km (40,400 sq.mile) . It is located at 22.59.degN. 88.42 deg.E,
The Bidhannagarh Municipal area is 31,30 sqkm approx.
o Drainage system:
I) SEWERAGE
a)Present Status:
The Bidhannagar Municipal town has an underground sewerage system along with some non-sewerage area also. The 277.1 km long sewerage system along with the metal road has varying diameter of 8”-33” and serves an area of 12.5 sq.km. There are Sewage Pumping Stations, 8 in number, to lift the sewage. The sewage is then pumped to the Bagjola Sewage Treatment Plant through a double-barrel Sewer line.
b) Existing System:
The total system has been functioning since 70’s. As no thorough cleaning has been done since then, the prevailing problem is siltation. The pumping equipments are also old and have poor efficiency. Besides these, due to the lack of public awareness, in various places and also in individual premises, storm-water line is connected with the sewer line transferring sediments into the system & causing the major source of blockage into the system.
II) STORM WATER DRAINAGE:
The most important factor on which the persistence of an Urban Area depends is its Drainage System. In Developing Countries like India very few Cities are planned in prior stage. Bidhannagar, being such a planned township has a proper underground separate drainage system (not combined). This helps a lot the Municipality to tackle many problem during the subsequent maintenance period.
o: Rainfall
As the Salt lake area remains within the extended part of Kolkata, the rainfall in this zone follows more or less a similar trend.
If we consider the rainfall records for the Kolkata area, it is observed that the average rainfall is to the tune of 1650 mm (record from 1967 to 1989). It is also noticed that the rainfall in a day even may exceed 200 mm occasionally. Whereas the drainage index adopted varies from 75 mm to 150 mm in a day. The total rainfall on successive three days estimated during 1978, 1984, 1986, and 1999 is up to the tune of 554.75 mm, 499.25 mm, 443.00 mm and 334.10 mm respectively. Whereas the drainage index adopted varies from 75 mm to 150 mm in a day . On an average, the kolkata city experiences about 4 to 6 water logging in a year. It is reduced after eighties.
o : General Description of the Salt lake Basin & its drainage net- work:
As it has already been discussed, that salt lake area is built up on re- claimed ground, filled up with sandy soil, over a swampy stretch of land on the eastern fringe of kolkatta. Therefore, the physical feature of the basin is more or less flat in nature. Average ground level of the basin is 12ft. The population density is quite high. Average population density is 15,590 sq .km. The overall area of Bidhannagarh Municipal is 31. 30 sq.km approx.
In consideration of the topography & outfall system, the catchment areas are broadly divided into 25 numbers followed by the ‘Master Plan of Drainage, Sewerage & Sanitation’ for 2001–2025. The Bidhannagar Municipal area is within the Northern Salt Lake Basin.
The outfalls of the planned township are two in number.
i) Kestopur Canal forms the Northern boundary of Bidhannagar Municipal area. One end is directly connected to river Hooghly in the West through New-cut canal — Circular Canal and the other end, passes down to the river Kultigung in the East through Kestopur- Bhangarkata khal.
The Circular canal, has bifurcation near Gaznavi Bridge as two separate and distinct canals. One part flows down towards Beliaghata as Circular –Beliaghata canal and other part passes down through New Cut- Kestopur-Bhangarkata to meet at Kultigong .
The Circular –Beliaghata canal is extended upto Chingrighata, E.M Bye-pass. From there, it is connected with an excavated channel named as the Eastern Drainage Channel along the South-Eastern boundary of Salt-Lake city under Bidhannagar Municipal area. This Eastern Drainage channel also has its outfall in the Kestopur Canal :
o: The drainage net-work:
From the Drainage point of view, the Kestopur Canal is the lifeline of the Bidhannagar area especially for the planned township of Salt lake.
o: Background & the past history Kestopur Canal:
It is already stated that at the present set up , one part of the Kestopur Khal is connected with the river Hooghly via New Cut Canal — Circular canal in the west ward direction and the other part with the river kultigong via Bhangarh kata Khal flowing easterly.
This canal system are presently serving as a drainage channel, catering the drainage discharge of Lake Town , Bangur , Dum Dum Park , Salt lake, Rajarhat , Bhangar and some other areas , either partially or fully. As the canals were started to use as the drainage channel, therefore, the sluices had been constructed at Chitpur and also at Kulti with provision of necessary tide lockage. Kestopur Khal forms the northern boundary of the Salt Lake City .
o: The past History of New –Cut-Kestopur- Bhangar Kata Khal :
Originally, due to increase in water traffic , it was necessitated to excavate a New Cut Canal which was started in 1855–56 and completed in 1856–59 . It may be pertinent to mention here that initially, it was a navigation channel with no gradient. The canal system takes off from Circular Canal about 275 meters south of Belgachia (Gaznavi) Bridge. River Bidyadhari at that time had a minor tributary viz Central Lake Channel, (15.30 Kms) in length which used to outfall into the river at Bamanghata , originally in Dhapa Bill . The Lake Channel was however heavily silted up in 1897 thereby leaving the only means of waterway communication in total disarray between Bamanghata and Dhapa . To provide navigational facilities in these areas, excavation of Kestopur Khal started in 1908–10. It used to take off from Aaratoon Jute Mill and outfalling into Bhangar Kata Khal which was excavated during 1897–98. The Kestopur –Bhangar kata Khal system outfalls into river Kultigong through an outfall system. The length of this canal system is about 34 Kms. The canal system was provided with navigational facility and was known as apart of “Inner Sundarban Route” and used as waterway connecting erstwhile East Bengal.
o: Present Set up:
The Bidhannagar Municipal area can be broadly classified into three areas according to the infra-structural facilities & socio-economic background. They are:
• The planned Salt Lake City
• The Slum area of Dattabad
• The Slums in the added area of Bidhannagar Municipality mainly comprising Ward no.14 & 23 (part of 22). Both of these Wards are environmentally important as they are enriched with the Wetlands of East Kolkata, a Ramsar Conservation Site.
o: The planned Salt Lake City: This area has completely separate underground drainage .Network with 184 km of pipe lines & a lifting/ pumping station. The drainage water of sector I & Sector -II (Part) is made to discharge directly to the Kestopur canal through a number of outlets and drainage water of Sec-III is also being discharged into Eastern Drainage through a number of outlets excepting Part of Sec.-III through drainage pumping station leading to Eastern Drainage Channel.
0 : Some important parameters:
I. The overall length of the Circular-New cut Canal- Kestopur- Bhangarh kata Canal :
i) Circular canal : 1.3 km ii) New cut canal : 2 km, iii ) Kristopur canal : 20 km ,iv) Bhangar kuta khal : 14 km = 37.30 km .
The entire canal system has no longitudinal slope and the bed level is maintained at (-) 0.60 M PWD & the full drainage depth (F.D.D) at 2.42 M. This keeps the full drainage level at R.L (1.82m.) i.e. 5.97ft.
o :Observations :
It is very pertinent to mention here that the normal drainage functioning of the entire Circular-New cut Canal- Kestopur- Bhangarh kata Canal system usually suffers from the tidal effect, both due to the river Hooghly as well as river kultigong , located at the two ends of the canal system.
The situation becomes grave in the consequence of heavy rainfall in Kolkata and adjoining areas, which further worsened if the event is coupled with the high tides in full noon & new moon period.
It is needless to mention here that the high ruling water level at Kestopur khal often invites a setback in the drainage process from the basin area of Bidhannagarh Municipality. It is not uncommon to experience that the kestopur khal , adjoining to Salt lake zone , is flowing higher than that of F.D Line i.e 5.97 ft ,followed by the effect of high rise in the water level of river Hooghly during the tidal period or releases of flood water down the river or having been coupled with both of those incidents. It is seen that at no of occasions, the water level of river Hooghly touches the level of 14ft and above . This results the drainage lockage at the outfall river and brings more complication in the flowing pattern of the khal and forces to rise the water level, even 3 ft to 4 ft beyond F.D line of Kestopur canal system.
We understand that the drainage water of the Salt lake basin area is either discharged directly into Kestopur khal through no of outlets or via Eastern Drainage Channel which is ultimately connected with Kestopur khal. Now, the efficacy of gravitational outflow of each of the outlet depends on the respective invert level condition vis-a -vis the F.D line of the drainage khal. Similarly, the outfall drainage level of Eastern drainage channel, if remains below the ruling water level of the Kestopur khal at the particular moment, there will be severe setback to cater drainage water through the system. Therefore, such lockage period to drain out water in a day, not only causes an increase in detention time, but also may effect the depth of water logging adversely.
Conclusion:
It is a fact that the Salt lake area has separate underground drainage system. This helps a lot to eliminate high deposition of sewerage, carrying in a domestic sewer line.
But, even so if the pipelines are not addressed /cleaned thoroughly from time to time , it may also cause heavy siltation accompanied in a storm water surface flow line .
So it may be required to address the cleaning process at regular interval time at each nodal point , i.e. i) at the catch pits, or ii) in the underground sewer lines etc.
Besides these, proper care should be taken that no individual domestic sewer line is connected with the separate Storm water line due to the lack of public awareness. This transfers sediments into the system & causing the major source of blockage into the system.
Apart that, we are all aware that the proper maintenance of the outfall canal system is also a major concern to all city drainage system.
Therefore, it needs to be monitored that the Full supply depth of Kestopur khal is always be made available so that the water may flow within the limit of F. D Line under normal condition.
We also understand that the flushing of Hooghly river water in the canal system is also necessary to safeguard against the environmental pollution and mosquito menace around its vicinity, though it may aggravate the sit deposition.
Thus, the action of frequent silt clearance is inevitable to maintain the canal at its original bed level. This will allow the ingress of storm water flow smoothly from its basin area through different inlets
Moreover, as the F.D Line of Easter Drainage Channel is not compatible to that of Kestopur Khal, particularly during the heavy incessant rainfall, therefore, we may think to install a lifting pumping station at the outfall confluence point, to facilitate the pumping drainage when the gravitational drainage flow remains blocked for high rise in water level in Kestopur khal exceeding F.D line. However, a physical model study may be useful to assess the actual lifting capacity of the proposed pumping station vis-a vis the drainage efficacy of Kestopur Khal.
