SAARC India Shankar Mahto Urban Flood Mgt Final

5/20/2018 SAARC India Shankar Mahto Urban Flood Mgt Final

Flooding in urban areas (urban flooding)

1.0 INRODUCTION

Flooding in urban areas can be caused by flash floods, or coastal floods, or river floods, butthere is also a specific flood type that is called urban flooding. Urban flooding is specific in thefact that the cause is a lack of drainage in an urban area. As there is little open soil that canbe used for water storagenearly all the precipitation needs to be transport to surface water orthe sewage system. High intensity rainfall can cause flooding when the city sewage systemand draining canals do not have the necessary capacity to drain away the amounts of rain thatare falling. Water may even enter the sewage system in one place and then get depositedsomewhere 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 whichtraditional probability based flood management policies might not provide adequateresponses. Furthermore, ongoing processes of urbanization (both expansion anddensification) increase susceptibilities of asset concentrations to floods, thus increasingoverall 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 thanwe currently get. The Environment Agency Sustainable DevelopmentUnit, said in June 2001:

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'Major floods that have only happened before say, every 100 years

on average, may now start to happen every 10 or 20 years. The floodseason may become longer and there will be flooding in placeswhere there has never been any before.'

Thus, the risk of flooding looks greater than ever and not just in one country or the other, butthroughout 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 inIndia. 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 high-value urban land for buildings are the cause of urban flooding. No. of water bodies in Delhiaccounting for about 800 had now remained 600 and rest vanished. Thousands of illegalcolonies have emerged in city and lack of well thought of planning of these areas haveresulted in constriction of natural drainage inviting urban floods. Thus proper urban planningand related sufficient drainage provisions for different areas covered under a city or townshipcan play a significant role in arresting the menace of urban flooding. The followings highlightcauses, effects, preventive measures to tackle urban flooding in Delhi & Mumbai

DEFINITION

A f lood 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

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a river, stream, or drainage ditch; or ponding of water at or near the point where the rain fell. Aflood can strike anywhere without warning, occurs when a large volume of rain falls within ashort time.

TYPES OF FLOODING

Accord ing to Durat ion 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'tabsorbed 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

Natural Causes

Heavy Rainfall / Flash floods

Lack of Lakes Silting

Human Causes

Population pressure Deforestation Trespassing on water storm drains Unplanned urbanisation is the key cause of urban flooding.Unauthorised colonies 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 aresummarised below:

Economic effects

Damage to Public buildings, Public utility works, housing and household 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, firecontrol, 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 hasadverse environmental impacts, effect on traffic, effect on human being in terms of theirlives, psychological impact, live stock, disease, public conveniences etc.

5/20/2018 SAARC India Shankar Mahto Urban Flood Mgt Final

2.0 Delhi Flooding A Case Study

Geography Delhi is located at latitude of 2834' N and a longitude of 77 07'E havingan 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: MunicipalCorporation of Delhi (MCD) - providing civic amenities to an estimated 13.78 millionpeople, New Delhi Municipal Council (NDMC) and Delhi Cantonment Board. Totalgeographic area of Delhi is 1483 sq.Km (Rural-689 Sq.Km, urban-624 Sq.Km andforest- 170 Sq.Km.). Delhi can be divided into three major geographical regions: theYamuna flood plain, the ridge and the Gangetic Plains.

Population: Delhi has attracted millions of people from Haryana, Punjab, UttarPradesh, 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 rural1200).In 2021, population of Delhi is

expected to 220 lac.

Climate of Delhi Delhi has a semi-aridclimate with high variation betweensummer and winter temperatures. Theaverage annual rainfall is approximately670 mm (27 inches), most of which fallsduring the Monsoons, in July and August.The flood season observed by DelhiGovernment is from July to October.

River Yamuna: River Yamuna, a major

tributary of river Ganges, originates fromthe Yamunotri glacier at an elevation ofabout 6387 meters above msl and itenters Delhi near Palla village makingcommon boundary with Uttar Pradesh(UP) and Haryana. The river flows inDelhi from Palla to Jaitpur for about 50Km length. It is trapped at Wazirabad forwater 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 insix drainage basins ultimately discharging into river Yamuna, namely- NajafgarhDrain, Barapulaah Nallah, Wildlife sanctuary area discharging thro' Haryana, Drainageof Shahdara area, Bawana drain basin and other drains directly out falling into riverYamuna. The National Capital territory (NCT) of Delhi is prone to flooding from riverYamuna, its catchment in Haryana and from Sahibi River (Rajasthan) via Najafgarhdrain. 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 pavedarea and decrease in the agricultural land which used to act as a percolation zone andis continuously depleting ( Net Agriculture area sown in 1950-51 was 97067 hac, in2005-06 is just 25000 hac out of total 148300 hac). Delhi normally remained flooded to

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the extent of 70000 hac (50% of its geographical area of 148300 hac from 1953 to1984).

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 Delhiwhen 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 rightmarginal bund between Palla and Bawana Escape out-fall also breached whichcaused a very large area of Alipur block and urban colonies like Adarsh Nagar, Modeltown, Mukerji Nagar submerged under deep water. On the left bank marginal bund

reached the point of distress but could besaved by raising its height in certain reacheswith earth filled bags. Damages nearly Rs.15crores, eighteen lives, thousands of peoplerendered homeless and10 lac people wereaffected. During floods in 1993, 206 localities,areas, colonies were inundated and flow oftraffic hampered in 130 stretches of roads.

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These floods alarmed the then Administrationand the Governmentt to appoint committeesand to take remedial measures to curbflooding in Delhi.

2.1.1 Heavy Rainfall/Flash floods: Theterritory of Delhi has been experiencingfloods mainly from Sahibi Nadi (passingthrough Najafgarh Drain) and Yamuna River

passing through Delhi. The local drainagesystem, at times, found to be inadequate tomeet the requirement, when there is heavyrain fall or during flash floods. Delhi normallyremained flooded to the extent of 70000 hac(50% of its geographical area of 148300 hacfrom 1953 to 1984).

2.1.2 Urbanisation: Due to fasturbanisation during last four decadesresulting in increase of paved areaand decrease in the agricultural land

which used to act as a percolationzone. Due to the growth of Delhi, thecatchment area of the Najafgarh drain

has been built up and paved resulting increase in water-flow during rainy season. Thecross-sectional area of the drain has become inadequate resulting in frequent floodingof areas along the drains. Same is the situation with River Yamuna and its flood plainin East Delhi. Further Rapid unplanned urbanisation is also a key cause offlooding.

2.1.3 Unauthor ised colonies There are about 1650 unauthorised colonies which have beendeveloped by the local colonisers on the open/agriculture land without consideration tothe city plans, drainage, sewerage etc. and thus subjected to flooding during heavyrain falls.

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2.1.4 Trespassing on storm water drains The areas which were essentially created bythe storm water drains (or constructed) to let their flood waters pass freely being tress-passed by Slum dwellers, small shopkeepers, motor garages, garbage dumping etcresult 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 dischargesediments into drains, flow of sewerage, sullage and solid waste materials into stormwater 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 oraround the city which acts as flood absorbers are gradually filled up and built upon dueto urbanisation pressure. Earlier 800 water bodies in Delhi, now reduced to only 600that 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 thedrains reduces water way. Garbage dumping in or on drains, near bridges also reducewater way.

2.1.8 Poor Water and Sewerage Management Old drainage and sewerage system has notbeen overhauled nor is it adequate now .All the drainage and sewer system in manyparts of Delhi has collapsed resulting in flooding. This can be seen during rainyseasons every year at Chhatarsal Stadium in model town, Minto Bridge, Bhairon roadRailway Bridge, ring road at Income Tax Office (ITO), Indra Prashta ( IP) Estate. Backflow 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 DelhiAdministration in 1981 considering problems and habitation at that point of time anddid not consider for future urbanisation and particularly rural-urbanisation andunauthorised colonies. Every department/ civic bodies in Delhi plan construct andmaintain their drainage in isolation without consideration of overall integrated drainageand sustainability resulting in flooding.

2.1.10 Failure of pumping installations due to inadequate capacity or the failure of electricsupply.

2.1.11 Multiple authorities in the city but owning responsibility by none. Less co-ordinationamong 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) andHaryana 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 andpresent Delhi Govt. has taken various preventive measures to curb floods in Delhiwhich resulted in safe living in Delhi to a great extent. These are illustrative and lotmore are yet be done.

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2.2.1 Construct ion of flood protection structures

Marginal Bunds on left bank of River Yamuna, Marginal bund on right bank u/s ofWazirabad 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 theembankments in Delhi territory. Raising of right embankment from Wazirabad barraged/s is under consideration for a discharge of 3 lac cusec.

Regulators with mobile pumping arrangement had been made where there is frequentrisk of main Drain/River flowing at higher level than maximum out fall level of out fallingdrains like at Chilla, Jahangirpuri drain, Supplementary drain and at all the 15 outfalling drains into River Yamuna.

Channelising, lining etc has been undertaken in Supplementary drain to cater for adesign discharge of 5000 cusec in first phase from Kakrola regulator, for 10000 cusecfrom Rithala d/s in Second phase and with 15000 cusec d/s of GTK Road in thirdphase. The proposal for phase II and III are under consideration.

With the construction of Ajmeripura Dam on Sahibi River in Rajasthan, Masani Barragein Haryana, and remodeling of Najafgarh drain including construction of supplementarydrain 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 materialsfrom all drains of all departments /civic bodies is being coordinated by the Engineer-in-Chief of Municipal Corporation of Delhi (MCD). The committee also to make sure thatall drains are checked and cleaned before monsoon to ensure that they are notblocked or collapsed. Desilting reports and certificates are being obtained from allowning agencies before 15thJune 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 drainsis being carried out by deploying about 28 machines (Dragline -18 Nos., Hydraulicexcavator water master-4 Nos with trucks, dozer, barges having total desilting capacityof 250 cum /hr though out the year. More machines are being purchased. Desiltingalso being carried out through contract where these machines can't be deployed.

Vasant Kunj, Mahipalpur and Dwarka area lack proper drainage system and sufferedflooding. The I &FC with DDA, PWD, Airport authority, CISF, MCD, Metro rail, railwaysetc. is working on it to work out a comprehensive plan on sharing basis using STPswith covered drain of ultimate 1000 cusec capacity

2.2.3 RAIN WATER HARVESTING Rain Water Harvesting is very old concept since ancienttimes and plays a key role in arresting floods and urban water scarcity. There aremany ways of rain harvesting as illustrated below adopted by Delhi Government whichwill go a long way in reducing urban floods. Construction of Ponds is another system ofrain 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 fromDhansa to Kakrola Regulator (by I &FC) by closing gates at Kakrola. 6.5 km ofNG Drain has also been deepened impounding 155 MG water annually andfurther 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.

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B. Arti ficial Recharge Trenches:49 nos (cost aprox 1.0 lac each) in bed of Mungeshpur drain in North WestDelhi in 7.3 km; 27 nos in borrow-area of Mundela Bund in 6.32 Km, 11 nos. inKhera Khurd storm water drain in 1.65 Km, 32 nos. in abandoned reach ofBurari escape drain in 4.85 Km in consultation with Central Ground WaterAuthority (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 AsolaWild Life Bird Sanctuary in hilly area of Delhi.These check dams have been proved veryeffective in 'flood protection and ground waterrecharge.

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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 lineto be developed.

E. Providing Retention basins:It is necessary to allocate certain areas to be usedas retention basins for detaining excess water toprevent flooding in low areas, road, and streets.The abandoned course of Bawana Escape drain atHaranki (near river Yamuna) has been developedby I&FC department in 58000 sq.m area

impounding river Yamuna's flood water. Yamuna's flood water is also divertedin to Bhalswa Lake. The Mungeshpur drain, NG Drain and The SD Drain arealso 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 followingmanner:-

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 removeiv. 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 preparedwhich 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 inbuilding plots more than 500 Sq. m in area including Roof top rain waterharvesting. Some Resident Welfare Society (RWS) are also voluntarilyadopting 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 floodplains. A lot of slum clusters and other structures along the banks and in theflood plains of river Yamuna have come up resulting in reduced flow. The Highcourt of Delhi has constituted Usha Mehra committee to remove all

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encroachments up to 300m from water edge. This has resulted in removal of allslum clusters and other structures reviving the original course and flood plain ofriver Yamuna. It will definitely help in more flow and retention of water duringfloods. Under Yamuna Action Plan -II - A coordinated efforts are being made byall department and civic bodies for total Water Cycle Management of Delhi inrelation to Yamuna and its flood plains.

2.2.5 Planting sturdy trees sustaining draught as well flooding: Stress has beengiven by the Government of Delhi for tree plantations where-ever land isavailable and particularly on road sides, along drains etc. Approximately5 00 000 trees are being planted every year. This will result in reducing soilerosion 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 inconsultation with all department of the government. These data shall beproperly documented and shall be used in planning and construction ofdrainage 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 ofthe city. The DDA, MCD and the Delhi Urban Art Commission have responsibility tostrictly follow the plans while developing the area.

Certain area has been declared as reserved forests where construction of any kindis prohibited

The land use and its planning in river New Yamuna is being looked by the DDA andsupervised 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 theChairmanship of the Hon'ble Chief Minister of Govt. of Delhi with all ministers ,MPs , some MLA and heads of all Government. /civic bodies looking afterdrainage, health, communication, food & supplies and dealing with basic amenitiesare its members with Chief Engineer (I & FC) its member-secretary. Central controlrooms are set up by MCD, NDMC, Police, Transport, Health, Home Guards & CivilDefence, Food & Civil Supplies, Flood Control department, Delhi DevelopmentAuthority, Education Department, PWD, Govt. of Delhi, BSES, NDPL, Delhi JalBoard 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 theDivisional Commissioner of Delhi.

Flood control Department installs 25 wireless stations, one central control roomconnected with other city control systems of various department Arrangement offlood materials like Empty Cement Bags-58500, Stone- 5714Cum, Ballies -2250,Boats-50, Life Buoy-211, Boat-Trolley-28, Boat Engine-24, Trucks-11, Life Jackets-471, Pumps-104 with pumping capacity of 330 cusecs, silt excavator machine -28Nos and Motorola sets to all officers had been made to curb the Delhi floods.

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The bench mark for alarming flood situation in Delhi is the water level of RiverYamuna at Old Railway Bridge. The Warning level is 204.0 m and danger level is204.83m. Warnings are also issued when discharge at Tajewala and Masanibarrages are- FIRST Warning at 1 00 000 and 35000 cusecs ,SECOND at 300 000and 70000 cusecs, THIRD warning at 5 00 000 and 100 000 cusecs are releasedfrom 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 afirst aid kit, canned food, bottled water, battery-operated radio, flashlight, protectiveclothing 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 andpromptness. Some of them are illustrated here.

A. By Government:- Evacuation priorities and needs, Identification of Evacuationsites, Evacuations during Un-expected flooding, Shelter management plan,Evacuation support plan, Live stock protections plan, Search and rescue of peopleand live stock, Setting up of Communications system, wireless system, controlrooms, Health operation and first aid. Immediate relief measures like supply offood, water, essential commodities, evacuations of flood victims; plugging ofbreaches, protection and emergency repairs of public transport system etc.

Pumping out water from low lying areas, (the I&FC department is having 205pumps with 2250 HP and capacity approx 330 cusecs which are used duringflooding in any area allotted to it in Delhi). Total DJB's Pumps-installations are 70Nos. with capacity of 1000cusec.

B. By Individual: - To use sandbags or pillows or rugs to fill the airspace of a doorduring rising flooding, put the expensive things, electronic appliances, food anddrinks upstairs or as high as possible, to switch off the power supply , to move to asafe and higher ground quickly. To be cautious at night, because it's harder to seeflood dangers. If told to evacuate, do so immediately. Avoid areas subject tosudden flooding like low spots or already flooded areas. Do not attempt to drivethrough a flooded road. The depth of the water is not obvious and the road may bewashed 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 floodmanagement team and obey instructions being given and cooperate and keeppatience.

3.3 Flood measures after cessation of floods:

Restoration of power installation, public assets like road, railways, bridges, sewerageand water supply schemes and drains, merchandise and shopping areas, industries /factory equipments, public building, etc. Demarcation of land lines & removal ofoverlapping sand/Silt layer of flooded area are to be done. System of post-monsoonsurveys needs to be done and corrective measures are adopted in time bound mannerto avoid flooding in future. Always to use boiled drinking water. Electrical equipmentshould be checked and dried before used.

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3.4 Failures of Flood Management Polic ies

Floods may or may not occur regularly. The level, duration, extent and terming of theiroccurrence vary from event to event. Where flood occur after long intervals, (it maycreate immediate crises) memory of crises also fades away and so the preparednessof flood management also disappear. Failure to adopt a comprehensive and effective

flood management policy may be due to:I. Lack of adequate fundsII. 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 Yamunaand 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 greatset back to civilizations. The preventive measures like improvement of drainageefficiency, construction of flood-protection structures, increasing areas around the cityto serve as retention basins, adopting rain water harvesting system, water rechargingof channels, etc are some of the preventive measures to curb urban flooding. The mainresponsibility in curbing the Delhi flooding rest with Irrigation and flood controldepartment of the Delhi Govt. which has taken many steps in this regard likestrengthening of embankments of river Yamuna, c/o supplementary drain and itsdeepening 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 bydeepening and lining in city area. The Najafgarh drain has also been used for waterretention. Check dams, recharge well, creation and revival of water bodies has alsobeen under taken by I &FC dept. Besides this, I&FC dept is also working out a freshdrainage plan of Delhi associating DJB, MCD, DDA, PWD etc to further take action oncurbing the flooding in Delhi. The political will is also of prime importance tocurb/reduce urban flooding by enacting legislations and getting it implementedfaithfully. A lot of experience has been gained with recurring floods in Delhi.

The territory of Delhi has been experiencing floods mainly from Sahibi Nadi (passingthrough Najafgarh Drain in Delhi) and Yamuna River. Moreover, local drainage systemhas also been, at times, found to be inadequate to meet the requirement, when there is

heavy rain fall or during floods.

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5.0 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 thenext 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,

grounding all flights for the day.

Overview

Thousands of school children were stranded due to

flooding and could not reach home for up to 24

hours. The following two days were declared asschool and college holidays by the state

government.

The city region and the suburbs that make up the

metropolis of Mumbai received 994 mm (39.1inches)

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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

5.3.1 Ant iquated 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.

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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 carryingcapacity to 50 mm per hour. The BMC committee had rejected the proposed project on the

grounds that it was "too costly.

5.3.2 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 wascreated 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 amajority of the city's drains already clogged. 'Heavy rains and high tide last year damaged themangrove 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 theriver and cause more flooding.

The Mithi river problem is identified into various areas. The first one is whether it canassimilate Mumbai's rainfall or not. For that the river should be clean, which is a curativeaction. The other one is preventive action, which means that sewage, which generates solidmatter, should be prevented from entering in to the river. BMC should first take steps toprevent the sewage. The people of Mumbai use the river as a dumping ground, whichcontains 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 veryfew sewage treatment plants, which is not even 10 per cent of what we require. So first weshould stop sewage entering the river. And for that we need proper sewerage system. So it allstarts from basic work. First, we have to treat the sewage in a proper way which helps reducewater pollution.

It's a myth that there is shortage of water. Actually, we have enough water, because as perstatistics 80 per cent rainwater goes back to the sea. We must harvest the rainwater everyyear. There should be collective efforts from industry owners and government. Governmenthas to take steps to ensure there is no scarcity of water. Fortunately, most civic bodies inmany states have made it mandatory to harvest rainwater for upcoming industries and

residential complexes.

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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 anexample to show the enormity of the problem.

The experience of floods in Mumbai and Chennai in 2005 has been one of the worst in therecent years. Amongst the metros, Mumbai is one place which is cosmopolitan. People fromall over the country try to seek jobs there and make a living. Many of them succeed. A stagecomes when they want to settle down there. The last floods have shaken all such would besettlers.

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 thegovernment and vice versa. The government tries its best to provide relief to people andassuage the feelings, but that does not help much. Post flood rehabilitation, health safety andreconstruction 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 ispossible 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 ofcarrying only 25 millimeter of rainwater per hour. With drains clogged at several places itproved inadequate for the 944mm rain which lashed Mumbai in one day alone. It seems thatonly three drains which drain into the sea have gates whereas, other 102 outlets have no suchgates. 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 withoutsaying that the drainage system needs a thorough overhaul with gates to man the backflow ofthe sea water. During the last floods of Mithi River the residents had to live under the constantfear of a deluge even after rains, just because high tide water was difficult to control. MithiRiver drains the Salsette Island on which the city of Mumbai is situated. Originating at Powaithe river flows through densely populated areas and industrial complexes of Powai, SakiNaka, 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 anddomestic waste all along have converted this natural drain to an open sewer. This river carriesthe excess water from Powai Lake. During the monsoon the river naturally swells. The riverused to act as a storm water drain for Mumbai. Now choked to capacity this natural facility isof 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 oranthropogenic reasons, coastal hurricanes and tsunamis and a combination of any of theabove can create havoc in the urban areas. If we revert back to Mumbai we realize the gentleslope of the ground is towards the sea. Water flows down the slope. During rains if the path ofwater is obstructed by buildings and the drains have no capacity, the outcome is what thepeople 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 thechannel of the river is made of clay at a particular site excess water will rather spill over as itwill not be able to go down to the depths. All these criteria have to be considered before

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planning development of a particular area. Unfortunately it is not so, and as a consequencemost 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 despitewarnings by the earth scientists. In order to save the residential area thus 'developed' massiveBunds 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 closedby the Bunds the city becomes a huge pool every monsoon. People blame the government fornot 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 morethan 40% mangroves have been 'reclaimed' in-between 1995 to 2005 by the builders andslum dwellers and the land has been constructed upon. Destruction of Mangroves along Mithiriver 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 theproblem of flooding for such centres. Yet if the people want to save themselves from the wrathof the floods and the government wants to avoid paying recurrent compensations to thepeople one of the way out is to construct large tanks where rain water could be stored andalso to puncture the ground at several places like it is done for rain water harvesting. Thiswould augment the seepage capacity of the ground. In addition a holistic drainage system forevery urban complex would save many a lives, economic losses and inconvenience due tofloods. 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, inmany countries can be destroyed instantly as a result of heavy rain andflooding. In recent months flooding in China and Bangladesh have leftthousands homeless. Whether those floods are due to climate change isdifficult to say, however they were examples of how some areas in the Worldstruggle to cope with such situations.

Although heavier precipitation is expected with human-induced global warming, other factorsplay a vital role. Deforestation can have a big impact as upland forests can soak up a lot ofwater, 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 somany 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 foragricultural purposes around the coast could be affected drastically which will obviously havea 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 levelsand 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 affecthuman lives considerably.

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7.0 Role of Urban Flood Modelling and Disaster Management

A change to proactive management of water-related disasters in urban areas requires anidentification of the risk, the development of strategies to reduce that risk, and the creation ofpolicies and programmes to put these strategies into effect. Computer-based modelling isinvaluable 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 acertain magnitude and frequency occur. Based on model results, various mitigation measurescan be evaluated to assess their ability for reducing risk exposure.

Different modelling approaches needs to be considered. They may range from data driven tophysically based, from conceptual to detailed 1D-2D modelling. These approaches are thenembedded in the wider context of flood risk assessment and disaster management. This widercontext considers everything from how the urban planning process should take place in areaswith potential flood risks, to urban hydrology, climate change, flood hazards, environmentalimpacts, public health issues and the conceptual design of flood protection schemes.

Reference:

I. nidm.gov.in/idmc/Proceedings/Flood/B2%20-%2036.pdf

Abbreviations:

CISF

:

Central

Industrial

Security

Force

CPWD: CentralPublicWorksDepartment

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: NewDelhiMunicipalCorporation

NDPL:NorthDelhiPowerLimited

PWD:

Public

Works

Department

STP:

Sewage

Treatment

Plant