AN OVERVIEW OF KOLKATA DRAINAGE SYSTEM & MAJOR OUTFALL CHANNELS
*The management of drainage system of Kolkata appears to be not satisfactory as per our desired level. Even at some places, a little precipitation is creating a good inconvenience to the inhabitants.
* Spread roughly north–south along the east bank of the Hooghly River, Kolkata sits within the lower Ganges Delta of eastern India; the city’s elevation is 1.5–9 m (5–30 ft). The general elevation of kolkata is nearly 14.26 ft. GTS near.
* Initially, the inhabitants were located on high lands and during rains the intervening low pockets served as temporary reservoirs, from which water slowly found its way through natural drains.
* But, the situation deteriorated as the town increased in size with the increase in population, and consequent to this, the natural drainage failed to function.
- In the last couple of years, a massive development work has been started, not only in the city, but all through the adjoining areas and different municipalities in the form of construction of Hospitals, Hotels, high rise residential and commercial buildings including housing complexes , many of which are coming up in large vacant low lying areas, undertaken at different levels .
- The city of Kolkota and added areas including different Municipalities of north & south 24 pgs have different outfall drainage channels.
- Each outfall drainage channel has particular design discharge capacity and full drainage level (F.D.Level).
- Therefore, any change in the land used plan in the Basin area of the respective Channel will impart excess pressure to particular drainage system to accommodate such additional discharge.
- Moreover, the change in land pattern resulted higher rise in the runoff index with reference to the existing one for which the pumping stations had been originally conceived in the city of Kolkata and suburban areas.
- Areas of high lands were small and were rapidly filled up and the town extended to different low areas.
- Thus, these low areas gradually ceased to function as temporary detention reservoirs and instead of, yielding more run off at the same time pressurising the overall drainage system.
- The core city of Kolkata had its underground drainage system introduced as back 1859–1875 as a combined sewerage system prior to the introduction of underground piped water supply from the surface water sources.
- When the underground drainage system was introduced, the city population was to the tune of 0.63 million and there were plenty of marshy lands, ponds, open spaces etc.
- Subsequently, the population explosion has been phenomenal which could not be anticipated by our town planners.
- The city’s population density has nearly doubled from 2039 persons per sq km in 1971 to 3879 persons per sq km townships to Kolkata’s east, the dominant growth in the past decade has been in the south-west covering Behala, Haridevpur, Maheshtala, Garden Reach . As per census report in 2011 , K.M.C has population 44.87 lakhs persons and the density of population stands as 23, 995 persons per sq.km.
- The KMC area is expanded a lot .At present the KM C is comprised of 141 wards with the overall area of 200.71 sqkm.
- As a result, the marshy lands, ponds etc. wherever available have been filled up indiscriminately and habitation started. This presented a great problem to the future town planners for affording desired civic amenities to the people.
*(II) DRAINAGE BASINS OF KOLKATA AND ITS OUTFALL RIVERS :
- Hemmed between Hooghly river on the west and Salt Lake to the east, the drainage of Kolkata and its adjoining areas are mainly dominated by two major outfall rivers.
- The river Hooghly in the west and
- Kultigong of Matla estuary system in the east.
- The S.W.F and D.W.F channel system , Kristopur -Bhangor kata khal etc. discharge storm water into Kultigong river.
- Along with, on the north, the drainage of Bagjola basin area is also being discharged into the Kultigong river.
- Whereas, the basins of Tolly’s nullah, Monikhali, Churial along with other minor drainage basins are draining into the Hooghly river in the west.
*(III) RAINFALL :
- If we consider the rainfall records for the last few decades in drainage pumping stations, 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, 1999 is up to the tune of 554.75 mm, 499.25 mm, 443.00 mm and 334.10 mm respectively.
- The northern part of the network (T.H.C. System) operated mainly Palmer Bazar Pump Station 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).
- On an average, the city experiences about 4 to 6 water logging in a year. It is reduced after eighties.
- Nearly 80% to 85% of the core city area and 50% of the total city area is covered with underground sewage and drainage system. Apart from these, the box drain of different sizes, katcha and pucca surface drains (open drains) of big sizes in some areas were constructed.
- However, the drainage disposal was entirely dependent on the network of main pumping stations linked with small pumping stations and boosting pumping stations.
- 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.
*(IV) KOLKATA DRAINAGE SYSTEM:
- A greater part of the core city of Kolkata is served by underground drainage system of the combined type in which both sewage and storm water flows through the same conduit.
- The slope of the ground of the city area is west to east in general.
- The sewers are also sloped in that direction.
- The area is very flat and low like the shape of saucer with scattered and localized pockets.
- The drainage water is lifted and discharged ultimately into the tidal river further down to the east through outfall channels.
- This was necessary to prevent pollution of the river Hooghly water which is used by the dwellers in the city for bathing and religious purpose.
*(V ) CHARACTERISTIC OF KOLKATA DRAINAGE SYSTEM :
- Due to its unique physical feature of Kolkata city (bowl shaped), the centre of the city is somewhat in lower elevation and as such every drop of waste water / storm water requires pumping to relieve water-logging.
- The situation is worsened in low pocket area, where the inundation takes for prolonged period because of earlier drainage in comparatively higher elevated areas.
- The worst effected areas are around Rabindra Sarani, Amherst St., Thanthania, Ballygunge Phari, Park Circus, Lansdown etc. where even a small amount of rainfall brings tremendous suffering to people, however , in the some of these low areas are improved a lot after installation of localized pumping station
- Moreover, due to unexpected growth of population, more and more people are settling in low lying marshy area around fringes of city which were originally vacant marshy land and played a vital role in the drainage system of the city instead now becomes chronically inundated zone.
- Besides, the city sewer system has no separate dry weather and storm weather arrangement, as a result, almost all the major and minor underground trunk sewer lines are badly silted up for absence of cleaning at regular interval and this has made the reduction in flowing capacity of storm weather flow to a considerable extent
- (VI) STORM WEATHER FLOW SYSTEM :
- The system is comprising of :-
- Suburban Head Cut (S.H.C) Channel is leading from Ballygunge pumping station to Bantala for a length of 7.32 km. with varing discharges from 900 cusec to 3850 cusecs at different reaches.
- During monsoon, it receives 900 cusec/ 1100cusec discharge from Ballygunge pumping station and 200 cusecs discharge from Bye pass regulator gates at Topsia. On its way to Bantala, it also receives 1450 cusec discharge from the 3 nos. pumping stations of Chowbhaga.
- One more pumping station with a capacity of 900 cusecs/1100 cusecs , recently was installed at Chowbhaga
* Town Head Cut (T.H.C) Channel is leading from Palmers bridge pumping station upto Bantala for a length of 7.80 km. with a design discharge of 1700 cusec .
* During monsoon, it receives 1564 cusec discharge from Palmers bridge, Kulia Tangra, Chingree Ghata & Pagla Danga pumping station. On its way to Bantala, at 5.03 km of T.H.C.channel, it also receives 720 cusec discharge from the feeder canal.
* Feeder to Town Head Cut (T.H.C) Channel is leading from Dhapa Lock pumping station upto Makalpota for a length of 1.82 km and for a discharge of 720 cusec. Thus, at the upstream of Bantala cross regulator gate , a storm discharge to the tune of (1700+720 )=2420 cusecs is likely to reach at the peak condition.
* At down stream of Bantala Regulator gate, the T.H.C.channel meets with S.H.C channel and the combined system is named as Storm Water Channel and it flows down upto Ghusighata to outfall into Kultigong river. Total length of S.W.F channel is 26.73 km.
* Other drainage channels like Kheyadaha khal, Sumidgiri khal, Karaidanga khal, Dudbibi khal, Bamunia khal outfall in this channel at different locations.
* It may be mentioned that the S.W.F. system caters discharge not only from the city of Kolkata, but also Suburban and rural areas where Kolkata proper with contiguous suburban areas of about 121 sq.km and that of contiguous rural area is 177 sq.km and together with it comes to 300 sq.km.
- It is worthwhile to mention that if all major pumping stations of the city are operated in full efficiency, the S.W.F channel has to be accommodated a discharge of about 6270 (3850 +2420) cusec at Bantala confluence point of SHC (3850 cusec ) & THC ( 2420cusec) Channel.
- Besides, the contiguous rural areas would contribute at least 1500 cusec in consideration of 20mm drainage index.
- Thus, in consideration of probable peak discharges at the different reaches of drainage system , the SWF channel likely to receive 7770 cusecs , say 8000 cusecs (approx),at the upstream side of Ghusighata sluice.
- Along with this, there is blockage in flow due to tidal lockage of 13 hours in a day on an average.
- Under this perspective, increase in the velocity of flowing water ,along the khal towards outfall sluices at Ghusighata is required to be done .This will not only help to accumulate more water in shorter duration at the upstream of outfall sluices ,but to facilitate disposing more forced water in the outfall river, namely Kultigong .This may require an installation of new pumping station , the capacity of which is to be evaluated after proper assessment, keeping in mind all hydro logical and physical parameters related to overall outfall system. .
* We may see that though S.W.F system originally mooted to disperse the drainage water from majority of city area , gradually it is becoming pressurized to receive more drainage water, yielding from Jadavpur and large part of newly developing area spread over either side of EM bypass. The contribution of drainage water from this part is quite heavy.
·*The S.W.F system receives water from Chowbhaga pumping stations under the scope of T.P canal & Intercepting channel drainage basin System . The overall basin area has 42.34 sq. km with seven sub-basins. The T.P system has its own basin of about 31.15 sq.km. The entire basin areas are becoming rapidly urbanized, linked with different lateral branches. Out of that, about 17 sq.km under KMC area within the Borough no VII , X & XII , spread over adjoining the EM by pass , is drained by forced pumping through Chowbhaga pumping station , for disposing into S.W.F System .
- Recently, the existing capacity of Chowbhaga pumping station( 1450 cusecs ) has been increased by 1000 cusecs( approx) to take care this area.
*(VII) KOLKATA DRAINAGE OUTFALL SYSTEM:
* As stated earlier, due to the physical feature of the KMC area, it is extremely dependent on pumping system for disposal of storm water.
* The main pumping station which disposes a major part of drainage flow are located at Palmerbazar, Dhapa, Ballygunge and Chowbhaga. Apart from it, there are small pumping stations i.e. Birpara, Duttabagan, Lake Town, Topsia, Kulia, Tangra, Chingrighata, Pagladanga etc. which discharge directly to different outfall channel.
* In addition to it, there are small lifting pumping stations for localized pocket area connecting the major pumping stations at Belgachia, Ultadanga, Maniktola, Nimakmahal, Mominpur, Chetla Lock, Jodhpur Park etc.
*However, in Northern part of the city area, about 300 cusec of water is discharged in Bagjola canal through several small pumping stations and where in the Southern most area like Behala, Garden Reach, the drainage is affected in the river Hooghly, though it faces considerable period of blockage during the high tide period.
*The Kolkata drainage outfall system mainly consists of S.W.F. & D.W.F. channels. The S.W.F. system which include both Town Head Cut (T.H.C.) and Suburban Head Cut (S.H.C.) channel, after receiving storm water discharge flows down further eastward direction for out falling at river Kulti, approximately 35 km away from the Ballygunge pumping station.
*But as the river Kultigong, being a tidal one, the S.W.F. can affect drainage only for a 5.5 hour in every 12 hr cycle, on an average.
*Moreover though the S.W.F. system caters mainly the city drainage, during its long distance flowing, it also receives drainage water from a city contiguous parts and also rural urban areas, which are developing rapidly.
*In this connection, a rough assessment has been made regarding the basin area that will effect discharge from the city core area through S.W.F (T.H.C and S.H.C channel) and other channel system, shown as follows.
1. Name of pumping station Basin area : PalmerBazar Pumping Station 4500 acre=18 sq.km.Considering, 150mm drainage index, approximate discharge arrived at 1500 cusecs.
2. Dhapa Lock Pumping Station : 2000 acre =8 sq.km.Considering, 100mm drainage index, approximate discharge is arrived at 432 cusecs.
3. Ballugunge Pumping Station: 5000 acre =20 sq.km.Considering 100mm drainage index, approximate discharge is arrived at 1100 cusecs.
4 a) Topsia Pumping Station. b) Kuila Tangra, Chingrahata & Pagladanga c) Through Lead Channel to Chowbhaga to S.H.C. Channel
The sub- basin areas of a) 900 acre =3.6 sq.km. b) 900 acre=3.6 sq.km, c) 666 acre =2.66 sq.km respectively . Now, considering 100mm drainage index, approximate discharge arrived at 200 cusec, considering 100mm drainage index, approximate discharge arrived at 200 cusecs, Considering 50mm drainage index, approximate discharge arrived at 75 cusecs in each cases of (a). (b) &© respectively .
5. Tollygaunge area including Kasba (through Lead Channel to Chowbhaga Pumping Station and ultimately to S.H.C Channel) : 2220 acre=8.90 sq.km.Considering 50mm drainage index, approximate discharge arrived at 250 cusecs.
6. Direct discharge to S.W.F. channel through inlet /lead channel etc. 4560 acre=18.24 sq.km. Considering 25mm drainage index, approximate discharge arrived at 256 cusecs.
7, the Cossipore — chitpore Basin 2000 acre =8 sq.km. Discharge to Bagjola / and river Considering 75mm drainage index, approximate discharge arrived at 340 cusecs.
8. Direct discharge into river Hooghly, Tolly’sNullah : 3250 acre =13 sq.km. Considering 75mm drainage index, approximate discharge arrived at 550 cusecs.
Total basin area considered as above : 104 sq. km
*From sl no.1 to sl no 6 above, it may be seen that the total basin area which effect discharge to S.W.F. channel system is approximately 83 sq.km.i.e. nearly 80% of Core city area and the balance area comprising of 21 sq.km (sl.7 and sl.8 ) cater discharge through mainly Bagjola Circular canal, Tolly’s Nullah and the river Hooghly.
*Further, it may be reiterated that on the basis of above drainage index as considered related to different basin areas of the respective pumping stations/ boosting stations, the approximate discharge has been arrived at 4013 cusec, which are likely to be generated from various sub-basins.
But. here it may be mentioned that the areas which still depend on gravitational flows i.e the condition of low lying areas where the discharge directly fed to outfall channels through lead channels etc. is very poor as they depend on F.D.Line of outfall of drainage channel ,which are exceeded often during the monsoon period.
We all aware that there is massive expansion in the original city area. At present, the KMC administrative area is comprised of 144 no of wards with a overall cover areas of 200.71sqkm. Such added city area can sustain the drainage index varying from 100 mm to 150 mm 24 hourly ,commensurate with the capacity of installed pumping stations .
The drainage from Jadavpur area & Tollygunge Panchannagram basin is effected to S.W.F. system through Chowbhaga Pumping Station and also to Tolly’s nullah .
The SWF system receives the drainage water from Chowbhaga pumping station. As entire entire area of TP & intercepting channel system , approximately of 42 sqkm, drains into SWF channel through forced pumping station for lack of gravitational flows ,it was necessitated to enhance the existing capacity of the puming station at Chowbhaga from 1450 cusecs to 2450 cusecs approx. .
On the other hand , the drainage from South Suburban and Garden Reach are affected through Churial and Monikhali Channel.
APART THAT OF SWF SYSTEM ,
BAGJOLA KHAL & TOLLY’S NULLAH ALSO TAKE AN IMPORTANT ROLE TO DRAIN OUT WATER FROM NORTHERN AND SOUTHERN PART OF THE CITY.
(v) OVERVIEW OF BAGJOLA KHAL :
The Bagjola khal is a major drainage artery catering discharges from a large part of areas comprised of 5 to 6 municipalities in northern part of the city of Kolkota along with newly upcoming areas of New town Project and New town planning area.
The Lower part of Bagjola being flown through New town project and Planning areas, where infrastructural development work is moving on phenomenally, causing immense pressure to release drainage water in the system.
The Bagjola khal drains both gravitational and pumped flow from its basin area due to tidal effect of outfall river Kultigong.
But, it is a fact that the pumped water would pressurise against the sustainability of carrying capacity of the Khal and accelerate the raising the F.D Line during the incessant rainfall.
Consequent to this, low lying basin areas depending on gravitational flow , will suffer prolong water logging till the ruling water level of the Lower Bagjola Khal is receded sufficiently to match with the ground levels .
It has been assessed that New Town Project Area would contribute to the tune of 100.85 cumecs in the bagjola khal from Ch2.5 km to Ch11.50. in the near future.
(VI) EVALUATION OF DRAINAGE WATER IN THE OVERALL PERSPECTIVE OF THE BASIN AREA UNDER BAGJOLA SYSTEM :
*The overall Bagjola Khal is comprised of two parts :
The upper part is named as Upper Bagjola khal : It starts from B.T Road and ends at V.I.P road crossing. The length of this stretch is 9.235 km.
The lower part i.e from V.I. P Road crossing to outfall point at Kulti river is called as Lower Bagjola Khal . The length of this stretch is 28.50 km.
*UPPER BAGJOLA KHAL (0.00 M. TO 9235.44 M.) :
Upper Bagjola Khal is the main drainage artery for the Urban Areas of Panihati,Kamarhati, Baranagarh ,North Dum-Dum,: Dum Dum, South Dum Dum and Adjoining Kolkata Municipal Areas.
The Basin area covers 56.57 sq.km. Land use pattern of the basin area is immensely changed during the last 20 yrs. The unplanned growth of the area changed the land used pattern which directly affect the drainage facility of the basin.
The present system of upper Bagjola Khal can cater discharge maximum in consideration of drainage discharge of D.I of 3inch per day.
However, after completion of various measures under different development Programme , the main drainage artery may improve to accommodate the storm discharge to the tune of 2258 cusecs with the higher drainage index of ( 5 inch to 6 inch per day)
Thus, at the tail end of Upper Bagjola Khal , down V.I.P road crossing, about 63.50 cumec of Discharge instead of 39 cumecs as prevailing now, would be flowed down through the Lower Bagjola khal after completion of the works under JNNURM Programme
* LOWER BAGJOLA KHAL , FROM V.I.P ROAD CROSSING TO THE OUTFALL AT KULTIGONG RIVER. (0.00 M. to 28.80 M.) :
The Lower Bagjola khal is mainly a carrier channel of Upper Bagjola khal for its disposal.
But, with the expansion of the city by filling the low lying areas ( which previously acted as a flood detention basin) on both sides of the channel, the area have virtually became a source of massive drainage yield impressing towards it. Hence, inadequacy in drainage capacity of the system became evident.
The shift of land use pattern has affected the existing drainage system adversely.
*The Lower Bagjola Khal is 28.8 Km. long and it starts from V.I.P. road crossing as a downstream continuation of Upper Bagjola Khal.
Lower bagjoia ends at Kulti Gong through nine and ten vents sluices at Kulti.
*The lower Bagjola basin may be divided into two parts.
- Upper part is within Ch. 0 Km. to 13.55 Km. has a total area of about 74 Sq.km.
- The New Town Project is situated within this part between 2.64 Km. to 13.55 km. and having area 30.87 Sq.Km.
- The rest 43.13 Sq.Km. is for the area outside of New Town Project.
*This outside of New Town Project area belongs under Rajarhat-Gopalpur Municipal urban area under Dist. North 24 Pgs
- Lower part of lower Bagjola basin is within Ch. 13.55 Km. to 28.8 Km. has a total area of about 31.5 Sq.krn. covering Bhangor I, Bhangor II and Haroa Blocks of Dist. South 24 Pgs.
- Therefore, total area of lower Bagjola Basin is 105.5 Sq,Km.
*TOLLY’S NULLAH (FROM CH 0.00 TO CH 15.50M )
- At present the Tolly’s Nullah ( from Ch 0.00 to Ch 15.50m ) is used as an important drainage artery serving a substantial area of the Southern part of the city. e.g Regent park, Bansdroni, Tollygunge, Alipore, Khidirpore including Keorapukur basin and also other areas adjoining to channel bank in the course of its 15.5 km travel path from Garia Railway bridge to Hastings on river Hooghly.
- However, beyond Ch 15.50 km, the bed slope of Tolly’s nullah remains in the easterly direction and continues upto Samukpota i.e Ch 28.50 km.
- This stretch of the Tolly’s Nullah is not functional at present due to heavy siltation and for want of upland flow of Hooghli water. Consequent to this, no drainage water is effected from either side of the basin through this stretch of Tolly’s Nullah.
- The Boat canal and Keorapukur Khal are the two tributaries of Tolly’s Nullah.
- Apart from drainage discharges, the two canals contribute considerable dry weather flow consisting mainly of untreated sewage water to the Toll’s Nullah at present.
- However, in the recent past, the basin area within the stretch from Garia Rail Bridge ( Ch 15.50 km) to Gangajoara i.e up to Ch 20.50 km , a rapid human growth is coming up with the severe changes in land use plan.
- Therefore, the issue of removal of drainage water from the instant part of the basin adjoining the length would be a great concern in near future.
- Incidentally, it may be stated that the topographical variation throughout the area in the zone of Hastings and Garia Rail Bridge i.e between Ch 0.00km to Ch 15.50km is relatively mild in variation, with high ground located along the banks of the Tolly’s Nullah and the boundaries of the Kolkata Corporation Suburban System area.
- The general slope of the ground along the Tolly’s Nullah is easterly however; on contrast the bed slope of the channel is Westerly i.e. in an opposite direction. This is mainly from Garia rail bridge to the outfall point at Hastings. The bed slope along this stretch is 1:5000. However, Garia rail bridge onward to Samukpota (i.e ch28.320km), the bed slope of Tolly’s Nullah follows easterly .
- The Kolkata Port Trust authority states that the Chetla Boat Canal was originally constructed as a navigation channel to facilitate removal of goods from the Khidirpore Docks.
- This function has been abandoned and the channel is used as a source of make-up for the dock basins. However, it carries the sewage and storm flow of K.P.T. area and is a good source of pollution of Tolly’s Nullah.
- Keorapukur sub- basin is served by Keorapukur Main khal and Keorapukur Western channel. A total basin area of 38.85 sq.km is drained at Tolly’s Nullah by Keorapukur main khal and Keorapukur western channel and Rania Khal.
- A pump house of 200 cusec capacity is installed at the end of Keorapukur western channel, which drains the water in the combined outfall channel of Keorapukur main and Western khal, and the discharge finally passes to Tolly’s Nullah through Kudghat sluice.
- Recently, the KEIP authority has also almost completed the construction another pump house for disposal of nearly 750 cusec discharge into Tolly’s Nullah.
- The basin area is relatively at lower level and unplanned rapid urbanization is taking place in the erstwhile rural areas.
(VIII) CIRCULAR — BELIAGHATA KHAL
- Circular Canal was originally, one of the principal navigation arteries , the pioneer in this process was Mr. Tiretta , the first planning and fixing up the alignment was prepared by him.
- The proposal was however turned down by Lord Wellesley . Another proposal was submitted by Major Scholch in 1824 but he died in 1826 in Anglo-Burmese War.
- Excavation of the canal was started in1829 and according to his proposal was completed in 1833.
- Chitpore Lock was also set up during this year.
- The Circular Canal , originally conceived as a navigational channel has no gradient originating at Chitpur , it bifurcates near Gaznavi Bridge (near R.G. Kar hospital) and terminates at E.M. By-pass , the length of this canal being 8.50 Kms .
- The eastern branch is known as New Cut Canal upto VIP Road Bridge.
- For some time past , the channel has been serving as drainage channel. The Circular Canal is connected with the Hooghly river at Chitpur through an outfall sluice and a navigational lock and with Eastern Drainage Channel near By-Pass.