«URBAN FLOODING AND ITS MANAGEMENT 1.0 INRODUCTION Flooding in general and urban flooding in particular is not a un- known event in world and in ...»
URBAN FLOODING AND ITS MANAGEMENT
Flooding in general and urban flooding in particular is not a un- known event in world and in India.
The un-even distribution of rain fall coupled with 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. The illegal filling of urban water bodies in cities like Calcutta, Delhi, and Hyderabad etc is a rampant. In Calcutta, for instance, Lake Town, badly situated, has not only suffered heavy floods in 1999 but also in 1970, 1978, 1984.The 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 planning has been thrown to the winds resulting in constriction of natural drainage inviting urban floods. This paper deals with causes, effects, preventive measures to tackle urban flooding in general with focus on Delhi, the capital city of India.
2.0 DEFINITION A flood is an excess of water (or mud) on land that's normally dry and is a SITUATION wherein the 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. This is a duration type event. A flood can strike anywhere without warning, occurs when a large volume of rain falls within a short time.
3.0 TYPES OF FLOODING
3.1 According to Duration Slow-Onset Flooding, Rapid-Onset Flooding, Flash Flooding.
3.2 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.
4.0 CAUSES OF URBAN FLOODING
4.1 Natural Causes 4.1.1 Heavy Rainfall / Flash floods Water of Heavy rainfall concentrates and flows quickly through urban paved area and impounded in to low lying area raising the water level. It creates more havoc when a main drain or a river passing through the area over-flows or breaches 4.1.2 Lack of Lakes Lakes can store the excess water and regulate the flow of water.
When lakes become smaller, their ability to regulate the flow become less and hence flooding.
4.1.3 Silting The drains carry large amounts of sediments and deposited in the lower courses making beds shallower thus channel capacity is reduced. When there is heavy rain, these silted drains can’t carry full discharge and result in flooding.
4.2 Human Causes 4.2.1 Population pressure Because of large amount of people, more materials are needed, like wood, land, food, etc. This aggravates overgrazing, over cultivation and soil erosion which increases the risk of flooding.
4.2.2 Deforestation Large areas of forests near the rivers/catchment of cities are used to make rooms for settlements, roads and farmlands and is being cleared due to which soil is quickly lost to drains. This raises the drain bed causing overflow and in turn urban flooding.
4.2.3 Trespassing on water storm drains The areas which were essentially created by the storm water drains to let their flood waters pass freely being tress-passed for developmental purposes result in obstruction of water flow and thus contributed immensely to the fury of floods.
4.2.4 Urbanisation leads to paving of surfaces which decreases ground absorption and increases the speed and amount of surface flow. The water rushes down suddenly into the streams from their catchment areas leading to a sudden rise in water level and flash floods. Unplanned urbanisation is the key cause of urban flooding. Various kinds of depression and low lying areas near or around the cities which were act as cushions and flood absorbers are gradually filled up and built upon due to urbanisation pressure. This results in inadequate channel capacity causing urban flooding.
4.2.5 Un Authorised colonies have been developed by the local colonisers on the agriculture land, earlier being used for crop has been purchased at lucrative prices from farmers, without consideration to the city plans,drainage, sewerage etc. and thus subjected to flooding during heavy rain falls.
4.2.6 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.
4.2.7 Lack of attention to the nature of hydrological system.
4.2.8 Lack of flood control measures.
4.2.9 Multiple authorities in a city but owning responsibility by none.
• 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 cause a great economic loss to the state, individual and to the society.
5.2. Environmental effects Damage to surroundings, forests, ridges, wild-life, zoo, urban community-trees, water bodies, shrubs, grass, fruits/vegetables in go downs etc result imbalance of eco-system of the city.
5.3. Effect on Traffic Flooding results in the damages of roads, collapse of bridges causing traffic congestion which affect day-to-day life and other transportation system.
5.4. Effect on Human Beings
• Human lives : Every year floods in India cause more than 50 lac people affected dead and become homeless.
• Psychological impact : The people of all ages who stranded in flooding suffer a great Psychological impact disturbing their whole life and the society as whole.
5.5. Live Stock : The live stock is the most affected living being due to urban floods. It is difficult to care for them particularly when human being itself is in trouble.
5.6. Disease : Flooding usually brings infectious diseases, e.g. military fever, pneumonic plagues, dermatopathia, dysentery, common cold, Dengue, break bone fever, etc. Chances of food poisoning also become more where electric supply interrupted in food-storage area due to flooding.
5.7. Public Inconveniences : The flooding causes impairment of transport and communication system due to which all people of all section get stranded e.g. school children, college students, office goers, vegetable, milk venders etc. The basic and essential commodities also do not reach to the common person. This result either starvation to poor persons or high priced to the common persons.
6.0 CASE STUDY - DELHI FLOODING Geography Delhi is located at a latitude of 28o34’ N and a longitude of 77o 07’E having an 6.1 average elevation of 233 m (ranging from 213 to 305 m) above the mean sea level. The NCT has three local municipal corporations: Municipal Corporation of Delhi (providing civic amenities to an estimated 13.78 million people), New Delhi Municipal Council (New Delhi) 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.
6.2 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.
6.3 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 Govt is from July to October.
6.4 River Yamuna The 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 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 and at Okhla barrages for regulating the water and then enters in UP.
6.5 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 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 1950-51was 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 fromTajewala) 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 home less 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 present Govt to appoint committees and to take remedial measures to curb flooding in Delhi.
DRAINS OF DELHI PATH OF YAMUNA
6.6 Reasons of flooding in Delhi 6.6.1 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).
6.6.2 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 Unplanned urbanisation is also a key cause of flooding.
6.6.3 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.
Many more are coming up which would further increase drainage congestion and flooding.
6.6.4 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 JJ Clusters, 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.
6.6.5 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.
6.6.6 Siltation water bodies Water bodies, low lying areas-water retaining plains, near or around the city which act 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 6.6.7 Chockage of water careers : 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.
6.6.8 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 ITO, IP estate. Back flow from main drains into city drains i/c sewers during high floods.