A flood is excess of water (or mud) on land that's normally dry and is a SITUATION wherein inundation of surrounding land area 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. Flooding is a duration type event. A flood can strike anywhere without warning, occurs when a large volume of rain falls within a short time.
Flooding in general and urban flooding in particular is not an unknown event in the world or 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 causes of urban flooding. Illegal filling of tanks and lakes and construction of multistoreyed residential complexes in their vicinity is the most common cause of urban flooding. Emergence of several illegal colonies resulting in constriction of the natural drainage system has resulted in rampant flooding.
Causes of Urban Flooding:
1. Natural Causes
* Heavy Rainfall / Flash floods
Water, during heavy rainfall concentrates and flows quickly through urban paved area and is impounded in to low lying areas raising the water level. It wreaks more havoc when a main drain or a river passing through the area over-flows or breaches.
* 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 occurs.
* Silting
The drains carry large amounts of sediments and deposit them in the lower courses making channel beds shallower. Thus channel capacity is reduced. When there is heavy rain, these silted drains cannot carry full discharge and results in flooding.
2. Human Causes
* Population explosion
Due to the ever increasing number of people, demand for more materials like wood, land, food, etc is on the rise. This aggravates overgrazing, over cultivation and soil erosion which increases the risk of flooding.
* Deforestation
Large areas of forests near the rivers/catchment of cities are used to make room 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.
* Trespassing on water storm drains
The areas which were essentially created by the storm water drains to let their flood waters pass freely are being trespassed for developmental purposes resulting in obstruction of water flow and thus contributing immensely to the fury of floods.
* 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 acted as cushions and flood absorbers are gradually filled up and built upon due to urbanisation pressure and space crunch. This results in inadequate channel capacity causing urban flooding.
* Unauthorised colonies
Agricultural sites have been converted to sites for residential and commercial layouts without consideration to the city plans, drainage, sewerage etc. and thus subjected to flooding during heavy rain falls.
* 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 the cities have collapsed resulting in flooding. This can be seen during rainy seasons every year.
* Lack of attention to the nature of hydrological system.
* Lack of flood control measures.
* Multiple authorities in a city but none own responsibility for the apathy.
EFFECTS OF FLOODING/ FLOOD DAMAGES
The flooding affects every section of people, systems in a city, some of them are
summarised below:
1. Economic effects
• 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. Flooding causes a great economic loss to the state, individual and to the society.
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 in imbalance of eco-system of the city.
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.
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 are stranded in flooding suffer a great Psychological impact disturbing their whole life and the society as whole.
5. Live Stock :
The live stock is one of the most affected living beings due to urban floods. It is
difficult to care for them particularly when human beings themselves are in trouble.
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 becomes more where electric supply gets interrupted in food-storage area due to flooding.
7. Public Inconveniences :
The flooding causes impairment of transport and communication system due to which all people of all sections 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 man. This results either in starvation of the poor or high priced commodities.
Friday, April 24, 2009
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