Flooding in urban areas (urban flooding)
Flooding in urban areas can be caused by flash floods, or coastal floods, or river floods, but there is also a specific flood type that is called urban flooding. Urban flooding is specific in the fact that the cause is a lack of drainage in an urban area. As there is little open soil that can be used for water storage nearly all the precipitation needs to be transport to surface water or the sewage system. High intensity rainfall can cause flooding when the city sewage system and draining canals do not have the necessary capacity to drain away the amounts of rain that are falling. Water may even enter the sewage system in one place and then get deposited somewhere else in the city on the streets.
1.1 EFFECT OF CLIMATE CHANGE
Climate change acts as a trend-breaker as well as creating a larger variability in the occurrence of extreme events. This result in increasing degrees of uncertainty towards which traditional probability based flood management policies might not provide adequate responses. Furthermore, ongoing processes of urbanization (both expansion and densification) increase susceptibilities of asset concentrations to floods, thus increasing overall vulnerabilities of urban areas to an increasing degree.
Although we can't say whether climate change caused the heavy rainfall, scientists predict we will see more heavy rainfall days in the future than we currently get. The Environment Agency Sustainable Development Unit, said in June 2001:
'Major floods that have only happened before say, every 100 years on average, may now start to happen every 10 or 20 years. The flood season may become longer and there will be flooding in places where there has never been any before.'
Thus, the risk of flooding looks greater than ever and not just in one country or the other, but throughout the whole World.
1.2 URBAN FLOODING AND ITS MANAGEMENT
Flooding in general and urban flooding in particular is not a un- known event in world or in India. The un-even distribution of rain fall coupled with rapid mindless urbanisation, encroaching upon and filling up natural drainage channels and urban lakes to use the highvalue urban land for buildings are the cause of urban flooding. No. of water bodies in Delhi accounting for about 800 had now remained 600 and rest vanished. Thousands of illegal colonies have emerged in city and lack of well thought of planning of these areas have resulted in constriction of natural drainage inviting urban floods. Thus proper urban planning and related sufficient drainage provisions for different areas covered under a city or township can play a significant role in arresting the menace of urban flooding. The followings highlight causes, effects, preventive measures to tackle urban flooding in Delhi & Mumbai
A flood is an excess of water (or mud) on land that's normally dry and is a SITUATION where inundation is caused by high flow, or overflow of water in an established watercourse, such as a river, stream, or drainage ditch; or ponding of water at or near the point where the rain fell. A flood can strike anywhere without warning, occurs when a large volume of rain falls within a short time.
TYPES OF FLOODING
According to Duration Slow-Onset Flooding, Rapid-Onset Flooding, Flash Flooding.
According to Location Coastal Flooding, Arroyos Flooding, River Flooding and Urban Flooding. The urban area is paved with roads etc and the discharge of heavy rain can't absorbed into the ground due to drainage constraints leads to flooding of streets, underpasses, low lying areas and storm drains.
1.2.1 CAUSES OF URBAN FLOODING
Heavy Rainfall / Flash floods
Lack of Lakes
Trespassing on water storm drains
Unplanned urbanisation is the key cause of urban flooding.
Poor Water and Sewerage Management
Lack of attention to the nature of hydrological system.
Lack of flood control measures.
Multiple authorities in a city but owning responsibility by none.
1.2.2 EFFECTS OF FLOODING/ FLOOD DAMAGES
The flooding affects every section of people, systems in a city. Some of them are summarised below:
• Damage to Public buildings, Public utility works, housing and house–hold assets.
• Loss of earning in industry & trade
• Loss of earning to petty shopkeepers and workers
• Loss of employment to daily earners
• Loss of revenue due to Road, Railway Transportation Interruption
• High prices for essential commodities.
After flooding, government has to put many resources for aiding e.g., police force, fire control, aid workers and for restoration of flood affected structures, persons, live-stock etc. The flooding causes a great economic loss to the state, individual and to the society. It has adverse environmental impacts, effect on traffic, effect on human being in terms of their lives, psychological impact, live stock, disease, public conveniences etc.
2.0 Delhi Flooding – A Case Study
Geography Delhi is located at latitude of 28°34' N and a longitude of 77° 07'E having an average elevation of 233 m (ranging from 213 to 305 m) above the mean sea level. The National Capital Territory (NCT) has three local municipal corporations: Municipal Corporation of Delhi (MCD) - providing civic amenities to an estimated 13.78 million people, New Delhi Municipal Council (NDMC) and Delhi Cantonment Board. Total geographic area of Delhi is 1483 sq.Km (Rural-689 Sq.Km, urban-624 Sq.Km and forest- 170 Sq.Km.). Delhi can be divided into three major geographical regions: the Yamuna flood plain, the ridge and the Gangetic Plains.
Population: Delhi has attracted millions of people from Haryana, Punjab, Uttar Pradesh, Rajasthan and Bihar. Population of Delhi in 1911was only 4.0 lac, in 1961 -
26.58 lac, in 1991- 70 lac and now it is 141 lacs. Population Density of Delhi is 9,294/km2 (Urban 12361 and rural 1200).In 2021, population of Delhi is expected to 220 lac.
Climate of Delhi Delhi has a semi-arid climate with high variation between summer and winter temperatures. The average annual rainfall is approximately 670 mm (27 inches), most of which falls during the Monsoons, in July and August. The flood season observed by Delhi Government is from July to October.
River Yamuna: River Yamuna, a major tributary of river Ganges, originates from the Yamunotri glacier at an elevation of about 6387 meters above msl and it enters Delhi near Palla village making common boundary with Uttar Pradesh (UP) and Haryana. The river flows in Delhi from Palla to Jaitpur for about 50 Km length. It is trapped at Wazirabad for water supply at ITO(Income Tax Office) and at Okhla barrages for regulating the
water and then enters in Uttar Pradesh (UP).
2.1 Floods in Delhi: From storm water drain point of view, Delhi can be divided in six drainage basins ultimately discharging into river Yamuna, namely- Najafgarh Drain, Barapulaah Nallah, Wildlife sanctuary area discharging thro' Haryana, Drainage of Shahdara area, Bawana drain basin and other drains directly out falling into river Yamuna. The National Capital territory (NCT) of Delhi is prone to flooding from river Yamuna, its catchment in Haryana and from Sahibi River (Rajasthan) via Najafgarh drain. The low-lying Yamuna flood plains (Khadar) are also prone to recurrent floods.
Due to fast urbanisation in Delhi during last four decades resulting in increase in paved area and decrease in the agricultural land which used to act as a percolation zone and is continuously depleting ( Net Agriculture area sown in 1950-51 was 97067 hac, in 2005-06 is just 25000 hac out of total 148300 hac). Delhi normally remained flooded to the extent of 70000 hac (50% of its geographical area of 148300 hac from 1953 to 1984).
The Capital of India has suffered floods as back as in1924, 1947, 1967, 1971, 1975, 1976, 1978, 1988, 1993, 1995, 1998 etc. The 1978 was the worst ever flood in Delhi when water level reached at 207.49 m (danger level is 204.83 m) with discharge 2.53 lac cusec at old railway bridge (7.0 lac cusec discharge was released from Tajewala) when130 villages and 25 urban colonies in Delhi were submerged in water. The right marginal bund between Palla and Bawana Escape out-fall also breached which caused a very large area of Alipur block and urban colonies like Adarsh Nagar, Model town, Mukerji Nagar submerged under deep water. On the left bank marginal bund reached the point of distress but could be saved by raising its height in certain reaches with earth filled bags. Damages nearly Rs.15 crores, eighteen lives, thousands of people rendered homeless and10 lac people were affected. During floods in 1993, 206 localities, areas, colonies were inundated and flow of traffic hampered in 130 stretches of roads.
These floods alarmed the then Administration and the Governmentt to appoint committees and to take remedial measures to curb flooding in Delhi.
2.1.1 Heavy Rainfall/Flash floods: The territory of Delhi has been experiencing floods mainly from Sahibi Nadi (passing through Najafgarh Drain) and Yamuna River passing through Delhi. The local drainage system, at times, found to be inadequate to meet the requirement, when there is heavy rain fall or during flash floods. Delhi normally remained flooded to the extent of 70000 hac (50% of its geographical area of 148300 hac from 1953 to 1984).
2.1.2 Urbanisation: Due to fast urbanisation during last four decades resulting in increase of paved area and decrease in the agricultural land which used to act as a percolation zone. Due to the growth of Delhi, the catchment area of the Najafgarh drain
has been built up and paved resulting increase in water-flow during rainy season. The cross-sectional area of the drain has become inadequate resulting in frequent flooding of areas along the drains. Same is the situation with River Yamuna and its flood plain in East Delhi. Further Rapid unplanned urbanisation is also a key cause of flooding.
2.1.3 Unauthorised colonies There are about 1650 unauthorised colonies which have been developed by the local colonisers on the open/agriculture land without consideration to the city plans, drainage, sewerage etc. and thus subjected to flooding during heavy rain falls.
2.1.4 Trespassing on storm water drains The areas which were essentially created by the storm water drains (or constructed) to let their flood waters pass freely being tresspassed by Slum dwellers, small shopkeepers, motor garages, garbage dumping etc result in obstruction of water flow and thus contributed immensely to the fury of floods. Most of the Delhi drains can be seen such trespassing and garbage dumping.
2.1.5 Siltation of drains Water treatment plants e.g. Bhagirathi, Haiderpur etc discharge sediments into drains, flow of sewerage, sullage and solid waste materials into storm water drains causing siltation which can't carry full discharge in heavy rain.
2.1.6 Siltation water bodies Water bodies, low lying areas-water retaining plains, near or around the city which acts as flood absorbers are gradually filled up and built upon due to urbanisation pressure. Earlier 800 water bodies in Delhi, now reduced to only 600 that too silted to a great extent. This results urban flooding.
2.1.7 Clogging of water carriers : Accumulation of dust, garbage chocked gully gratings, bell mouths of roads and inlets of street drains, passing of cables, pipes across the drains reduces water way. Garbage dumping in or on drains, near bridges also reduce water way.
2.1.8 Poor Water and Sewerage Management Old drainage and sewerage system has not been overhauled nor is it adequate now .All the drainage and sewer system in many parts of Delhi has collapsed resulting in flooding. This can be seen during rainy seasons every year at Chhatarsal Stadium in model town, Minto Bridge, Bhairon road Railway Bridge, ring road at Income Tax Office (ITO), Indra Prashta ( IP) Estate. Back flow from main drains into city drains & sewers during high floods.
2.1.9 Deficiencies in the drainage system (Planning, Execution & Maintenance):- The master plan for drainage of Delhi was prepared in 1976 and sent to Delhi Administration in 1981 considering problems and habitation at that point of time and did not consider for future urbanisation and particularly rural-urbanisation and unauthorised colonies. Every department/ civic bodies in Delhi plan construct and maintain their drainage in isolation without consideration of overall integrated drainage and sustainability resulting in flooding.
2.1.10 Failure of pumping installations due to inadequate capacity or the failure of electric supply.
2.1.11 Multiple authorities in the city but owning responsibility by none. Less co-ordination among various Government and civic bodies like MCD, PWD, DJB, I&FC, BSES, NDPL, NDMC. Cantonment area, CPWD etc. Control of Operation of barrages at ITO, Chilla and Okhla on river Yamuna are not with Delhi but with Uttar Pradesh (UP) and Haryana which regulate only at request of I&FC dept of Delhi.
2.2 PREVENTIVE MEASURES UNDER TAKEN/PLANNED
After every flood in Delhi and experience gained, then Delhi Administration and present Delhi Govt. has taken various preventive measures to curb floods in Delhi which resulted in safe living in Delhi to a great extent. These are illustrative and lot more are yet be done.
2.2.1 Construction of flood protection structures
• Marginal Bunds on left bank of River Yamuna, Marginal bund on right bank u/s of Wazirabad was constructed. These act as barriers for flooding.
• Regulators were constructed on Najafgarh drain.
• After floods of 1978, the banks of river Yamuna has been raised, a large number of spurs, bed bars, studs and Left Forward bund have been constructed to protect the embankments in Delhi territory. Raising of right embankment from Wazirabad barrage d/s is under consideration for a discharge of 3 lac cusec.
• Regulators with mobile pumping arrangement had been made where there is frequent risk of main Drain/River flowing at higher level than maximum out fall level of out falling drains like at Chilla, Jahangirpuri drain, Supplementary drain and at all the 15 out falling drains into River Yamuna.
• Channelising, lining etc has been undertaken in Supplementary drain to cater for a design discharge of 5000 cusec in first phase from Kakrola regulator, for 10000 cusec from Rithala d/s in Second phase and with 15000 cusec d/s of GTK Road in third phase. The proposal for phase II and III are under consideration.
• With the construction of Ajmeripura Dam on Sahibi River in Rajasthan, Masani Barrage in Haryana, and remodeling of Najafgarh drain including construction of supplementary drain has reduced the flooding in Delhi.
2.2.2 Improvement of drainage efficiency
• Desilting, cleaning of road, bell mouth, gullies, removal of debris, solid waste materials from all drains of all departments /civic bodies is being coordinated by the Engineer-inChief of Municipal Corporation of Delhi (MCD). The committee also to make sure that all drains are checked and cleaned before monsoon to ensure that they are not blocked or collapsed. Desilting reports and certificates are being obtained from all owning agencies before 15th June every year.
• Constructions of Najafgarh drain for 100-150 cusec capacity flow.
• Najafgarh drain, Supplementary drain, Jahangirpuri drain, Shahdra out fall drains etc carry lot of silt from domestic sewers and therefore continuous desilting of these drains is being carried out by deploying about 28 machines (Dragline -18 Nos., Hydraulic excavator water master-4 Nos with trucks, dozer, barges having total desilting capacity of 250 cum /hr though out the year. More machines are being purchased. Desilting also being carried out through contract where these machines can't be deployed.
• Vasant Kunj, Mahipalpur and Dwarka area lack proper drainage system and suffered flooding. The I &FC with DDA, PWD, Airport authority, CISF, MCD, Metro rail, railways etc. is working on it to work out a comprehensive plan on sharing basis using STPs with covered drain of ultimate 1000 cusec capacity
2.2.3 RAIN WATER HARVESTING Rain Water Harvesting is very old concept since ancient times and plays a key role in arresting floods and urban water scarcity. There are many ways of rain harvesting as illustrated below adopted by Delhi Government which will go a long way in reducing urban floods. Construction of Ponds is another system of rain harvesting used particularly in villages where land in normally not costly.
A. On-channel storage of Rain Water in storm drains:
Rain Water is being impounded in 30 km length of Najafgarh (NG) Drain from Dhansa to Kakrola Regulator (by I &FC) by closing gates at Kakrola. 6.5 km of NG Drain has also been deepened impounding 155 MG water annually and further 2.3 km is proposed to be deepened by 1.5 m. Mungeshpur drain has been regarded in 12.5 km impounding 4 MG water.
B. Artificial Recharge Trenches:
49 nos (cost aprox 1.0 lac each) in bed of Mungeshpur drain in North West Delhi in 7.3 km; 27 nos in borrow-area of Mundela Bund in 6.32 Km, 11 nos. in Khera Khurd storm water drain in 1.65 Km, 32 nos. in abandoned reach of Burari escape drain in 4.85 Km in consultation with Central Ground Water Authority (CGWA) have been provided. Similar trenches in other drains are also proposed to be provided.
C. Check Dam:
13 Check Dams had been constructed in Asola Wild Life Bird Sanctuary in hilly area of Delhi. These check dams have been proved very effective in 'flood protection and ground water recharge.
D. Development and deepening of village ponds:
150 ponds have been developed and deepened
all over Delhi which will impound 300 MG water, 175 ponds are under pipe line to be developed.
E. Providing Retention basins:
It is necessary to allocate certain areas to be used as retention basins for detaining excess water to prevent flooding in low areas, road, and streets. The abandoned course of Bawana Escape drain at Haranki (near river Yamuna) has been developed by I&FC department in 58000 sq.m area
impounding river Yamuna's flood water. Yamuna's flood water is also diverted in to Bhalswa Lake. The Mungeshpur drain, NG Drain and The SD Drain are also used as retention basin at their out fall. F. Creation/Revival of water bodies:
In Delhi, there are about 600 water bodies on record which are being revived and developed to take rain water. Government of National Capital Territory (NCT) of Delhi has issued direction to develop these water bodies in following manner:-
i. To survey all water bodies up to its catchment area.
ii. To remove all encroachments coming in catchment area. iii. To provide drain if encroachment is not possible to remove iv. To provide Sewage Treatment Plant's so that sewerage/sullage do not enter into water bodies.
v. To deepen the water bodies up to its protecting/impervious layer.
vi. To provide plantation around and in catchment areas to reduce erosion. With these directions of the Government., the schemes are being prepared which would cost approx 500 crores and would arrest flood situation in Delhi besides increase in water wealth.
G Rain Water Harvesting Structures:
Buildings-bye laws have been modified to provide rain water harvesting in building plots more than 500 Sq. m in area including Roof top rain water harvesting. Some Resident Welfare Society (RWS) are also voluntarily adopting this system in their colonies by good campaign of the Government.
2.2.4 Flood-plain management:
The Yamuna Development Board, Yamuna Action plan-I, Yamuna Action plan- II and Usha Mehra committee etc are working for river Yamuna and its flood plains. A lot of slum clusters and other structures along the banks and in the flood plains of river Yamuna have come up resulting in reduced flow. The High court of Delhi has constituted Usha Mehra committee to remove all encroachments up to 300m from water edge. This has resulted in removal of all slum clusters and other structures reviving the original course and flood plain of river Yamuna. It will definitely help in more flow and retention of water during floods. Under Yamuna Action Plan -II - A coordinated efforts are being made by all department and civic bodies for total Water Cycle Management of Delhi in relation to Yamuna and its flood plains.
2.2.5 Planting sturdy trees sustaining draught as well flooding: Stress has been given by the Government of Delhi for tree plantations where-ever land is available and particularly on road sides, along drains etc. Approximately
5 00 000 trees are being planted every year. This will result in reducing soil erosion and run-off coefficient of the area and in turn reduce the flooding.
2.2.6 I&FC dept has started preparing of Master drainage plan of Delhi in consultation with all department of the government. These data shall be properly documented and shall be used in planning and construction of drainage system of Delhi.
2.2.7 Land use and development planning
• Delhi Development Authority (DDA) has been given responsibility to prepare master plans considering drainage aspects besides others for the development of the city. The DDA, MCD and the Delhi Urban Art Commission have responsibility to strictly follow the plans while developing the area.
• Certain area has been declared as reserved forests where construction of any kind is prohibited
• The land use and its planning in river New Yamuna is being looked by the DDA and supervised by the Central Water Commission, Delhi.
3.0 FLOODING MANAGEMENT- SAFETY TIPS
3.1 Before flooding:
A. By Government :-An Apex committee for flood -mitigation is working under the Chairmanship of the Hon'ble Chief Minister of Govt. of Delhi with all ministers , MPs , some MLA and heads of all Government. /civic bodies looking after drainage, health, communication, food & supplies and dealing with basic amenities are its members with Chief Engineer (I & FC) its member-secretary. Central control rooms are set up by MCD, NDMC, Police, Transport, Health, Home Guards & Civil Defence, Food & Civil Supplies, Flood Control department, Delhi Development Authority, Education Department, PWD, Govt. of Delhi, BSES, NDPL, Delhi Jal Board and all connected to control room of CWC.
Guidelines on floods and complete information of nodal persons, arrangements, list of vulnerable points are issued as "Flood Control Orders" every year by the Divisional Commissioner of Delhi.
Flood control Department installs 25 wireless stations, one central control room connected with other city control systems of various department Arrangement of flood materials like Empty Cement Bags-58500, Stone- 5714Cum, Ballies -2250, Boats-50, Life Buoy-211, Boat-Trolley-28, Boat Engine-24, Trucks-11, Life Jackets471, Pumps-104 with pumping capacity of 330 cusecs, silt excavator machine -28 Nos and Motorola sets to all officers had been made to curb the Delhi floods.
The bench mark for alarming flood situation in Delhi is the water level of River Yamuna at Old Railway Bridge. The Warning level is 204.0 m and danger level is 204.83m. Warnings are also issued when discharge at Tajewala and Masani barrages are- FIRST Warning at 1 00 000 and 35000 cusecs ,SECOND at 300 000 and 70000 cusecs, THIRD warning at 5 00 000 and 100 000 cusecs are released from these barrages. The warning level in Delhi has been attained every year except in 1987, 1991 and 2004.
B. By Individual: - Flood insurance policy for house should be procured. To have a disaster plan and to prepare a disaster supply kit for home and car. To include a first aid kit, canned food, bottled water, battery-operated radio, flashlight, protective clothing and written instructions on how to turn off electricity, gas, and water.
3.2 During flooding:
These are the measures required on site with highest degree of efficiency and promptness. Some of them are illustrated here.
A. By Government:- Evacuation priorities and needs, Identification of Evacuation sites, Evacuations during Un-expected flooding, Shelter management plan, Evacuation support plan, Live stock protections plan, Search and rescue of people and live stock, Setting up of Communications system, wireless system, control rooms, Health operation and first aid. Immediate relief measures like supply of food, water, essential commodities, evacuations of flood victims; plugging of breaches, protection and emergency repairs of public transport system etc.
Pumping out water from low lying areas, (the I&FC department is having 205 pumps with 2250 HP and capacity approx 330 cusecs which are used during flooding in any area allotted to it in Delhi). Total DJB's Pumps-installations are 70 Nos. with capacity of 1000cusec.
B. By Individual: - To use sandbags or pillows or rugs to fill the airspace of a door during rising flooding, put the expensive things, electronic appliances, food and drinks upstairs or as high as possible, to switch off the power supply , to move to a safe and higher ground quickly. To be cautious at night, because it's harder to see flood dangers. If told to evacuate, do so immediately. Avoid areas subject to sudden flooding like low spots or already flooded areas. Do not attempt to drive through a flooded road. The depth of the water is not obvious and the road may be washed away. Kids should never play around high water, storm drains or viaducts. Keep listening to the latest news and announcements from the police or local flood management team and obey instructions being given and cooperate and keep patience.
1.3 Flood measures after cessation of floods:
Restoration of power installation, public assets like road, railways, bridges, sewerage and water supply schemes and drains, merchandise and shopping areas, industries / factory equipments, public building, etc. Demarcation of land lines & removal of overlapping sand/Silt layer of flooded area are to be done. System of post-monsoon surveys needs to be done and corrective measures are adopted in time bound manner to avoid flooding in future. Always to use boiled drinking water. Electrical equipment should be checked and dried before used.
1.4 Failures of Flood Management Policies
Floods may or may not occur regularly. The level, duration, extent and terming of their occurrence vary from event to event. Where flood occur after long intervals, (it may create immediate crises) memory of crises also fades away and so the preparedness of flood management also disappear. Failure to adopt a comprehensive and effective flood management policy may be due to:
I. Lack of adequate funds
II. Flood problems are technically complex and prediction of next occurrence is difficult.
III. Multiplicity of department /local authorities and Lack of coordination amongst these bodies.
4.0 Outcome of Such Exercise
Delhi has suffered heavy floods in past due to rapid mindless urbanisation, encroaching upon and filling up natural drainage channels and urban lakes and water bodies to use the high-value urban land for buildings, illegal colonies and industries, increase in paved area, heavy downpours over Delhi and heavy discharges in Yamuna and Sahibi river. The flooding has several impacts /effects on human-lives, animals, trees, plantations, eco-system of the area. If not taken seriously, it may cause a great set back to civilizations. The preventive measures like improvement of drainage efficiency, construction of flood-protection structures, increasing areas around the city to serve as retention basins, adopting rain water harvesting system, water recharging of channels, etc are some of the preventive measures to curb urban flooding. The main responsibility in curbing the Delhi flooding rest with Irrigation and flood control department of the Delhi Govt. which has taken many steps in this regard like strengthening of embankments of river Yamuna, c/o supplementary drain and its deepening and lining to increase its carrying capacity to 5000 cusecs. The carrying capacity of Najafgarh drain has also been increased from 5000 to 10000 cusecs by deepening and lining in city area. The Najafgarh drain has also been used for water retention. Check dams, recharge well, creation and revival of water bodies has also been under taken by I &FC dept. Besides this, I&FC dept is also working out a fresh drainage plan of Delhi associating DJB, MCD, DDA, PWD etc to further take action on curbing the flooding in Delhi. The political will is also of prime importance to curb/reduce urban flooding by enacting legislations and getting it implemented faithfully. A lot of experience has been gained with recurring floods in Delhi.
The territory of Delhi has been experiencing floods mainly from Sahibi Nadi (passing through Najafgarh Drain in Delhi) and Yamuna River. Moreover, local drainage system has also been, at times, found to be inadequate to meet the requirement, when there is heavy rain fall or during floods.
Maharashtra floods of 2005
Maharashtra floods of 2005 created flooding in many parts of the Indian state of Maharashtra including large areas of the metropolis Mumbai, a city located on the coast of the Arabian Sea, on the western coast of India, in which at least
1,000 people died. On 27 July, an unprecedented heavy rainfall of 94.40 cm was recorded at Santacruz (Mumbai). It was a devastating rainstorm that crippled the lifeline, infrastructure at Mumbai for days together.
The floods were caused by the eighth heaviest ever recorded 24-hour rainfall figure of 944 mm (37.16inches) which lashed the metropolis on 26 July 2005, and intermittently continued for the next day. 644 mm (25.4 inches) was received within the 12-hr period between 8am and 8pm. Torrential rainfall continued for the next week. The highest 24-hour period in India was 1,168 mm (46.0 inches) in Aminidivi in the Union Territory of Lakshadweep on 6 May 2004. The previous record high rainfall in a 24-hour period for Mumbai was 575 mm (22.6 inches) in 1974.Other places severely affected were Raigad, Chiplun, Ratnagiri and Kalyan in Maharashtra and the southern state of Goa.
The rains slackened between the 28 July and 30 July but picked up in intensity on July 31. The Maharashtra state government declared 27 and 28 as a state holiday for the affected regions. The government also ordered all schools in the affected areas to close on August 1 and August 2. Mumbai Police commissioner Anami Narayan Roy requested all residents to stay indoors as far as possible on July 31 after heavy rains disrupted the city once again,
India's western coast receives high rainfall due to the presence of the Western Ghats which lie at about 50 km (30 miles) from the coast. The hill range runs parallel to the Indian coast at an average altitude of 1,200 metres (3,900 ft). Rain bearing clouds generally deposit much of their moisture through orographic rainfall along India's western coast which lies on the windward side of the hills.
5.1 Financial effect
The financial cost of floods was unprecedented and these floods caused a stoppage of entire commercial, trading, and industrial activity for days. Preliminary indications indicate that the floods caused a direct loss of about Rs. 450 crores (€80 million or US$100 million). The financial impact of the floods was manifested in a variety of ways:
• The banking transactions across the counters were adversely affected and many branches and commercial establishments were unable to function from late evening of 26 July 2005. The state government declared the 27th (and later, 28th) of July as a public holiday.
• The Bombay Stock Exchange and the National Stock Exchange of India, the premier stock exchanges of India could function only partially. The Exchanges, however, remained closed for the following day.
5.2 Effect on Mumbai's links to the rest of the world
• For the first time ever, Mumbai's domestic and international airports (including Chatrapati Shivaji International Airport, Sahar and Juhu aerodrome) were shut for more than 30 hours due to heavy flooding of the runways and extremely poor visibility. Over 700 flights were cancelled or delayed. The airports reopened on the morning of 28 July 2005. Within 24 hours of the airports becoming operational, there were 185 departures and 184 arrivals, including international flights. Again from early morning of 31 July, with increase in water logging of the runways and different parts of Mumbai, most of the flights were indefinitely cancelled.
• Rail links were disrupted, and reports on late evening of 30 July indicated cancellation of several long distance trains up to 6 August, 2005.
• The Mumbai-Pune Expressway, which witnessed a number of landslides, was closed the first time ever in its history, for 24 hours.
5.3 Factors aggravating the disaster in Mumbai
1.a.1 Antiquated drainage system
The existing storm-water drainage system in Mumbai was put in place in the early 20th century and is capable of carrying only 25 millimetres of water per hour which was extremely inadequate on a day when 944 mm of rain fell in the city. The drainage system is also clogged at several places. Only 3 'outfalls' (ways out to the sea) are equipped with floodgates whereas the remaining 102 open directly into the sea. As a result, there is no way to stop the seawater from rushing into the drainage system during high tide.
In 1990, an ambitious plan was drawn to overhaul the city's storm water drainage system. A project costing approximately 600 crore rupees was proposed by consultants hired by the Brihanmumbai Municipal Corporation (BMC) to study the issue. The project was planned to have completed by 2002 and aimed to enhance the drainage system through larger diameter storm water drains and pipes, using pumps wherever necessary and removing encroachments. The project, if implemented would have doubled the storm water carrying capacity to 50 mm per hour. The BMC committee had rejected the proposed project on the grounds that it was "too costly.”
1.a.2 Destruction of mangrove ecosystems
Mangrove ecosystems which exist along the Mithi River and Mahim Creek are being destroyed and replaced with construction. Hundreds of acres of swamps in Mahim creek have been reclaimed and put to use for construction by builders. These ecosystems serve as a buffer between land and sea. It is estimated that Mumbai has lost about 40% of its mangroves between 1995 and 2005, some to builders and some to encroachment (slums). Sewage and garbage dumps have also destroyed mangroves. The Bandra-Kurla complex in particular was created by replacing such swamps.
5.4 Future Plan for Mumbai
There are two actions which should be applied to the Mithi river - curative and preventive. BMC has to focus more on preventive action as compared to the curative.
'The failure to implement the ban on the use of plastic bags has added to the problem with a majority of the city's drains already clogged. 'Heavy rains and high tide last year damaged the mangrove wetlands on the city's outskirts. Silt removed from the Methi river has been dumped in the wetlands. The silt accumulated in the mangrove wetlands will be washed back into the river and cause more flooding.
The Mithi river problem is identified into various areas. The first one is whether it can assimilate Mumbai's rainfall or not. For that the river should be clean, which is a curative action. The other one is preventive action, which means that sewage, which generates solid matter, should be prevented from entering in to the river. BMC should first take steps to prevent the sewage. The people of Mumbai use the river as a dumping ground, which contains almost 60 per cent city's garbage. If the garbage is removed Mithi will flow smoothly. So far, BMC has done only 5 to 10 per cent work on cleaning the Mithi river.
5.5 Major steps taken to prevent water pollution?
The first and the foremost is that pollution in India is due to domestic sewage. We have very few sewage treatment plants, which is not even 10 per cent of what we require. So first we should stop sewage entering the river. And for that we need proper sewerage system. So it all starts from basic work. First, we have to treat the sewage in a proper way which helps reduce water pollution.
It's a myth that there is shortage of water. Actually, we have enough water, because as per statistics 80 per cent rainwater goes back to the sea. We must harvest the rainwater every year. There should be collective efforts from industry owners and government. Government has to take steps to ensure there is no scarcity of water. Fortunately, most civic bodies in many states have made it mandatory to harvest rainwater for upcoming industries and residential complexes.
6.0 Urban Floods: Bane for the People
The floods caused a direct loss of Rs. 450 crores or US $ 100 million. This was just an example to show the enormity of the problem.
The experience of floods in Mumbai and Chennai in 2005 has been one of the worst in the recent years. Amongst the metros, Mumbai is one place which is cosmopolitan. People from all over the country try to seek jobs there and make a living. Many of them succeed. A stage comes when they want to settle down there. The last floods have shaken all such would be settlers.
The ire of the Mithi 'nadi' in Mumbai was such that it caused imponderable loss of life, property, public facilities, interrupted all activities and above all worse was the daily wagers. The stoppage of work left them high and dry. In such circumstances people curse the government and vice versa. The government tries its best to provide relief to people and assuage the feelings, but that does not help much. Post flood rehabilitation, health safety and reconstruction is a big burden on the exchequer that comes all of a sudden and unexpected.
Flooding is not a new phenomenon. The recent experience has however, shown that sudden, incessant rains are the major factor behind deluges. Well one cannot control the rains, but it is possible to tame and utilize the flood waters in urban areas.
Let us take example of Mumbai. The reasons which led to massive flooding include, antiquated drainage system. The 20th century drainage network of Mumbai is capable of carrying only 25 millimeter of rainwater per hour. With drains clogged at several places it proved inadequate for the 944mm rain which lashed Mumbai in one day alone. It seems that only three drains which drain into the sea have gates whereas, other 102 outlets have no such gates. Problem with coastal areas is lack of adequate gradient for water to flow into the sea. During high tides, the sea water incursion takes place through these drains. Drains without gates become vulnerable points and a salt water deluge engulfs upcountry. It goes without saying that the drainage system needs a thorough overhaul with gates to man the backflow of the sea water. During the last floods of Mithi River the residents had to live under the constant fear of a deluge even after rains, just because high tide water was difficult to control. Mithi River drains the Salsette Island on which the city of Mumbai is situated. Originating at Powai the river flows through densely populated areas and industrial complexes of Powai, Saki Naka, Kurla, Bandra-Kurla complex, Dharavi and Mahim where it meets the Arabian Sea. Dense clusters of slums right on the river bank, disposal of industrial waste, sludge and domestic waste all along have converted this natural drain to an open sewer. This river carries the excess water from Powai Lake. During the monsoon the river naturally swells. The river used to act as a storm water drain for Mumbai. Now choked to capacity this natural facility is of no help during the rains.
Current Science says that the mechanism of urban flooding is complex and site specific. Heavy rains, river overflowing the banks, sudden release of water from dams due to natural or anthropogenic reasons, coastal hurricanes and tsunamis and a combination of any of the above can create havoc in the urban areas. If we revert back to Mumbai we realize the gentle slope of the ground is towards the sea. Water flows down the slope. During rains if the path of water is obstructed by buildings and the drains have no capacity, the outcome is what the people of Mumbai experienced in 2005.
Floods in the rivers are dependent on topography, drainage, rainfall and the ground geology. For example, if the drainage is poor as in Mumbai even less rainfall will cause floods. If the channel of the river is made of clay at a particular site excess water will rather spill over as it will not be able to go down to the depths. All these criteria have to be considered before planning development of a particular area. Unfortunately it is not so, and as a consequence most of the cities are flood prone.
Lucknow, the Capital of Uttar Pradesh never had the problem of water logging. A posh colony, Gomtinagar, a dream of politicians and builders came up on the bank of Gomti River despite warnings by the earth scientists. In order to save the residential area thus 'developed' massive Bunds were constructed all along the route of the river throughout the city. It is common sense that the natural slope of the ground in a city on the banks of a river is towards the river. Rainwater just moves down the slope to reach the river. The approaches of water been closed by the Bunds the city becomes a huge pool every monsoon. People blame the government for not cleaning the drains and the government blames the people for choking them. Unfortunately no one realizes that water-logging has been actually 'invited'.
The coastal areas have mangroves as buffers between the land and the sea. In Mumbai more than 40% mangroves have been 'reclaimed' in-between 1995 to 2005 by the builders and slum dwellers and the land has been constructed upon. Destruction of Mangroves along Mithi river near Mahim creek is one of the root causes of sea water incursion during tides.
The urban areas have been constructed upon and now it is too late to plan and tackle the problem of flooding for such centres. Yet if the people want to save themselves from the wrath of the floods and the government wants to avoid paying recurrent compensations to the people one of the way out is to construct large tanks where rain water could be stored and also to puncture the ground at several places like it is done for rain water harvesting. This would augment the seepage capacity of the ground. In addition a holistic drainage system for every urban complex would save many a lives, economic losses and inconvenience due to floods. Seepage holes will prevent water-logging and the menace of the mosquitoes.
6.1 The World
For many people around the World, particularly in developing countries, the dangers associated with flooding are serious. Houses, or even shacks, in many countries can be destroyed instantly as a result of heavy rain and flooding. In recent months flooding in China and Bangladesh have left thousands homeless. Whether those floods are due to climate change is difficult to say, however they were examples of how some areas in the World struggle to cope with such situations.
Although heavier precipitation is expected with human-induced global warming, other factors play a vital role. Deforestation can have a big impact as upland forests can soak up a lot of water, but if humans are destroying these areas the water has more land it can run to, increasing the risk to homes and people. Wetlands can also soak up a lot of moisture, but so many are now drained to make room for development that their disappearance also hinders the flooding risk.
Coastal areas around the World will also be threatened as sea levels rise. Land used for agricultural purposes around the coast could be affected drastically which will obviously have a large impact on livelihoods.
Of the largest 15 cities in the World, 13 of them are on coastal plains - with rising sea levels, they may have to do a lot of work on their defences to prevent disasters.
What will need to be weighed up in every corner of the globe is the impact rising sea levels and increased precipitation could have on them, what can be done to prevent this and how to adapt to it. Action and no action could be very costly financially, but doing nothing could affect human lives considerably.
7.0 Role of Urban Flood Modelling and Disaster Management
A change to proactive management of water-related disasters in urban areas requires an identification of the risk, the development of strategies to reduce that risk, and the creation of policies and programmes to put these strategies into effect. Computer-based modelling is invaluable for this purpose. It is used for assessing the potential for a hazard to occur and a vulnerability analysis to provide an understanding of the consequences should an event of a certain magnitude and frequency occur. Based on model results, various mitigation measures can be evaluated to assess their ability for reducing risk exposure.
Different modelling approaches needs to be considered. They may range from data driven to physically based, from conceptual to detailed 1D-2D modelling. These approaches are then embedded in the wider context of flood risk assessment and disaster management. This wider context considers everything from how the urban planning process should take place in areas with potential flood risks, to urban hydrology, climate change, flood hazards, environmental impacts, public health issues and the conceptual design of flood protection schemes.
CISF : Central Industrial Security Force
CPWD: Central Public Works Department DDA : Delhi Development Authority DJB: Delhi Jal Board
I&FC: Irrigation & Flood Control
MCD: Municipal Corporation of Delhi
MLA : Member of Legislative Assembly
MP : Member of Parliament
MSL : Mean Sea Level
NDMC: New Delhi Municipal Corporation NDPL: North Delhi Power Limited
PWD: Public Works Department STP: Sewage Treatment Plant