Flood Case Study - Cw
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Flood Case Study Chrison Wong Geography 12IB
Lag Response Flooding
Flash Flooding
Caused by heavy rainfall in a short period of time (less than 6 hours) or less commonly, a sudden release of water such as a dam failure or ice dam collapse The ground becomes saturated with water and is unable to drain surface run-off quickly enough, so water collects in low areas
Caused by prolonged rainfall or other inputs such as melting ice Relatively long term – days or weeks Flooding is due to rising water in an existing waterway (i.e. river, stream) which overflows its banks
Ethiopia 2006
(Flash Flooding in a LEDC)
The Dechatu River, which bisects Dire Dawa, flooded within a period of 3 hours due to heavy rainfall. Police fire guns into the air to warn citizens of the flooding. The flood killed 250 people and displaced 10,000 people, more than half of which are still living in tents today. Many building and homes were destroyed. The flood prompted the town to build sand banks
Switzerland 2005 (Lag Flooding in a MEDC)
The Aare River, which runs through Bern, flooded after days of torrential rainfall. Almost 1000 people were evacuated. The flood killed 6 people and caused $800 million in damage Infrastructure such as electrical and water systems were damaged. After the water subsided, almost all people returned to their homes immediately, and repairs began within days.
Ganges River Basin
Ganges: Causes of Floods
The Ganges Delta in Bangladesh and India is situated at the confluence of the Ganges River, the Brahmaputra, and the Meghna River. Heavy monsoon rain from June to September and synchronization of the flood peaks of all three rivers cause annual flooding of the region.
Ganges: Human Impact
The two major dams on the Ganges are the Haridwar and Farraka dams. The Haridwar dam diverts water from the river to the Upper Ganges Canal to irrigate the surrounding area. The Farraka dam is used to produce hydroelectricity. Dams reduce the velocity and competence of the river, causing more deposition. This raises the level of the river bed and hence significantly increases the chance or flooding upstream of the dam.
Ganges: Human Impact cont’d
Rapid population growth in the Indian subcontinent has increased demand for agricultural land and wood for fuel and construction, which has encouraged deforestation in the upstream areas on the Ganges The removal of vegetation reduces the amount of water which is removed from the system through interception and subsequent evapotranspiration, and increases the rate of percolation and throughflow. Both of these factors increase the risk of flooding downstream. Deforestation also increases the rate of
Nile River
Nile: Human Impact
The Aswan Dam, which was built to generate hydroelectricity and irrigate the area, has lowered the base flow of the Nile and no longer allows the Nile to flood annually. The sediments in the river are now held behind the dam, which cause several problems:
The Lake Nasser Reservoir is slowly filling up with sediment, increasing the risk of flooding in the region. As the water capacity of the reservoir decreases in the future, this presents a risk of dam failure. The land downstream is now infertile because the silt which replenished the land when the river flooded its banks no longer arrives. The highly populated Nile Delta is at risk of flooding because there is very little sediment coming down the Nile to replenish the sediments lost from erosion of the coastline.
Works Consulted
British Broadcasting Corporation. (2005). Floods Sweep Across Switzerland. El-Sayed, Sayed & van Dijken, Gert L. (2008). The southeastern Mediterranean ecosystem revisited: Thirty years after the construction of the Aswan High Dam Integrated Regional Information Networks (IRIN). (2008). Ethiopia: Thousands displaced by flash flood in Gambella. UNHCR Refworld. Internet Geography. (2008). Drainage Basin. Khalequzzaman. (1998). Recent Floods in Bangladesh Possible Causes and Solutions. Mukerjee, Amitahba. (1998). The Ganga Basin.
Lag Response Flooding
Flash Flooding
Caused by heavy rainfall in a short period of time (less than 6 hours) or less commonly, a sudden release of water such as a dam failure or ice dam collapse The ground becomes saturated with water and is unable to drain surface run-off quickly enough, so water collects in low areas
Caused by prolonged rainfall or other inputs such as melting ice Relatively long term – days or weeks Flooding is due to rising water in an existing waterway (i.e. river, stream) which overflows its banks
Ethiopia 2006
(Flash Flooding in a LEDC)
The Dechatu River, which bisects Dire Dawa, flooded within a period of 3 hours due to heavy rainfall. Police fire guns into the air to warn citizens of the flooding. The flood killed 250 people and displaced 10,000 people, more than half of which are still living in tents today. Many building and homes were destroyed. The flood prompted the town to build sand banks
Switzerland 2005 (Lag Flooding in a MEDC)
The Aare River, which runs through Bern, flooded after days of torrential rainfall. Almost 1000 people were evacuated. The flood killed 6 people and caused $800 million in damage Infrastructure such as electrical and water systems were damaged. After the water subsided, almost all people returned to their homes immediately, and repairs began within days.
Ganges River Basin
Ganges: Causes of Floods
The Ganges Delta in Bangladesh and India is situated at the confluence of the Ganges River, the Brahmaputra, and the Meghna River. Heavy monsoon rain from June to September and synchronization of the flood peaks of all three rivers cause annual flooding of the region.
Ganges: Human Impact
The two major dams on the Ganges are the Haridwar and Farraka dams. The Haridwar dam diverts water from the river to the Upper Ganges Canal to irrigate the surrounding area. The Farraka dam is used to produce hydroelectricity. Dams reduce the velocity and competence of the river, causing more deposition. This raises the level of the river bed and hence significantly increases the chance or flooding upstream of the dam.
Ganges: Human Impact cont’d
Rapid population growth in the Indian subcontinent has increased demand for agricultural land and wood for fuel and construction, which has encouraged deforestation in the upstream areas on the Ganges The removal of vegetation reduces the amount of water which is removed from the system through interception and subsequent evapotranspiration, and increases the rate of percolation and throughflow. Both of these factors increase the risk of flooding downstream. Deforestation also increases the rate of
Nile River
Nile: Human Impact
The Aswan Dam, which was built to generate hydroelectricity and irrigate the area, has lowered the base flow of the Nile and no longer allows the Nile to flood annually. The sediments in the river are now held behind the dam, which cause several problems:
The Lake Nasser Reservoir is slowly filling up with sediment, increasing the risk of flooding in the region. As the water capacity of the reservoir decreases in the future, this presents a risk of dam failure. The land downstream is now infertile because the silt which replenished the land when the river flooded its banks no longer arrives. The highly populated Nile Delta is at risk of flooding because there is very little sediment coming down the Nile to replenish the sediments lost from erosion of the coastline.
Works Consulted
British Broadcasting Corporation. (2005). Floods Sweep Across Switzerland.
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