Flooding Case Study: LEDC – Bangladesh
Bangladesh is located in south asia, adjacent to inida. Its location plays a major role in the occurrence of tropical storms and therefore the flooding. Having a coast to the warm waters of the indian oceans means tropical forms can form and attack the Bangladeshi coast.
The Causes of the Flooding
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Bangladesh has always been a natural hotspot for flooding. There are, in general, two major causes of the flooding, the fluvial flooding and the cyclonic flooding.
The major causing of the flooding is due to the fluvial snowmelt in the high Himalayas. When this is combined with the monsoon rain there is a peak amount of discharge in the three major rivers of the area.
When it isn’t the monsoon season, heavy rainfall on the hills and flood plains of Bangladesh causes similar results to monsoon rain. If anything this causes can be more damaging even though the flooding is less severe, people are less prepared outside of the monsoon season. Flash floods are caused by heavy rainfall in and flooding of the surrounding rivers. These have been made worse recently due to the increase in deforestation in the area.
The other major source of flooding is down to the storm surge floods, cyclonic. These are caused by cyclones and hurricanes entering the Bay of Bengal. The great storm surges which result destroy everything in their path. They have built embankments to prevent the storm surges, but this has caused drainage congestion. The embankments have prevented the back flow of floodwater into the river. In this way, embankments have sometimes led to the increase siltation of channels, making the flooding worse.
Benefits of the floods
Although the floods cause devastation to Bangladesh it provides many benefits that can’t be overlooked. The floodwaters are used to replenish ground water reserves. Without ground water reserve the Bangladeshi people would run out of drinking water, which would be even more serious. The waters also provide nutrient-rich sediment for farming production. The sediment helps vegetables grow in the otherwise hostile conditions.
The waters also provide an environment for the fish to live and grow. Especially as in Bangladesh fish is the major source of food. Economically it is very important as it provides 10% of annual export earnings. The aftermath of the floods provide ideal for algae growth that is valuable for the fertilizers used. When the floodwaters wash everything away it almost cleanses the area and pollutants are taken away from domestic areas.
The Flood Action Plan
Even though the flooding provides many benefit to the area the risk to human life is too great, meaning a plan needed to be put into action to control the flooding. Everyone can see that the task of totally preventing flooding is impossible; the plan was more to control the flooding than anything else.
The way in which control could be best achieved is creating a system of embankments along the major rivers. But these embankments are not meant to be able to withstand the major flooding events. This means that the expected annual flooding will be prevented but the disasters such as the flooding of 1991. They are meant to provide some control of flooding to give a more regular regime. This means that seasonally the floods will be prevented giving the people better safety, but for obvious reasons doesn’t remove the threat of flooding. The embankments are fitted with sluices, which are used to slow the rivers discharge and velocity, which means erosion in the river can be controlled as well.
The embankments were built away from the river for two purposes. The first was to keep them away from the erosive power of the river, to maintain the embankment. But also this has the advantage that they are very inexpensive. The installation and maintenance is affordable even for an LEDC such as Bangladesh. It also means that the area between the river and embankment can be cultivated. The collected floodwater can even be used for the successful shrimp industry of Bangladesh.
The Objections to the Flood Action Plan
* When the embankments are breached the damage caused will be much greater because of the sudden nature of the discharge. Natural flooding would be more natural meaning the damage would be less.
* The sluices have caused huge arguments. Many say they are too ineffective to work efficiently. People argue over who has the say about the use of the sluices as people downstream are effected by the decisions of that person.
* Sudden breaches of the embankments may also deposit deep layers of infertile river sand over the land, dramatically decreasing fertility.
* The algae naturally produced by the flooding will be affected meaning natural fertilizers are removed.
* Embankments increase the period of flooding, since they prevent back flow into the rivers.
* The flushing of pollutants will therefore not occur meaning a high percentage of agrochemical on the land and therefore in the food chain.
* The stagnant water created by the embankments could lead to the evolution of disease.
* As wetlands dry out biodiversity decreases meaning a loss to the environment.
* Without the flooding ground water levels will vastly reduce.
* People will have to be moved for the construction of the embankments.
It seems that although the protection and safety of the people is very important the economic and social disadvantages of the plan are too great. The amount of problems created is huge as the environment, economy and society is affected for the safety of fluvial flooding. So, although the people are protected from the flooding the disastrous flooding still remains a hazard, so the amount of progress accomplished is limited.
The effectiveness and impact of flood defences in Kutubdia island
Kutubdia Island is located on the east coast of Bangladesh in the Bay of Bengal. When the flood action plan was put into place Kutubdia was one of the places where the defences were put into place.
In many areas along the islands coast sea walls have been constructed to prevent the velocity of the storm surges. This way the surges themselves disappear before hitting the land. This means that it is now more possible to cultivate land closer to the coast without the risk of losing the crop due to storm surges.
There have been many sites of embankments across the island, such as the road shown the picture. This means that the not only is the area behind the road protect but communication systems are kept pretty much in tact due to this added protection
There has construction of storm shelters to protect the islands inhabitants in the case of a storm. It is built of reinforced concrete and the platform 25feet above sea level offering excellent protection to the people.
Along with this there has been much rebuilding on the island. Many of the houses before the 1991 flooding were poorly constructed and simply washed away. The reconstruction process meant the use of reinforced concrete. This picture shows the newly built market town of Kutubdia that contains new concrete buildings, which are obviously safer for the residents.
The defences show that there is now safety for people on the island. But apart from evacuating the coastal lowlands and living above 5m there are no strategies that will completely eliminate the prospect of flooding.
Extra Information: Video
* 29th April 1991 Tropical Cyclone hit east coast.
* 140,000 died.
* 1 in 3 drowned.
* Low lying area, prone to flooding.
* High density population, living near the coast on low land.
* Earth wall protects to some extent.
* Most Bangladesh is below 15m sea level.
* Warm waters, above 27oC, provide frequent tropical storms.
* Cyclone Bunkers were built on stilts to protect people from the rising floodwaters.
* Warnings were issued, including local people to warm everyone about the approaching storm.
* Surge broke embankment, people who hadn’t gone to shelters were exposed.
People live in vulnerable area for:
* Fishing is rife by the coast. To earn sufficient money, the fishing is needed.
* Farming is also present to some extent.
* Prawn farming is good in salt-water areas, providing living for many.
* Provides many jobs, as the packing and exporting of the fish and prawns are very important to Bangladesh.
* This large amount of economic activity makes wages twice the national average.
Plans for future:
* Tree planting programs, help stabiles soil, protecting villages and embankments.
* Earth Embankments.
* Cyclones shelters. ï¿½80,000 each.
* Public awareness of the shelters