3.9 Coastal flooding Flashcards
What is some context information about Bangladesh?
-world’s most densely populated country, with an estimated population of 169 million in 2015
-46% of the country’s population lives less than 10 metres above sea level
-Bangladesh lies on the floodplains of three major rivers- the Brahmaputra, Meghna and Ganges- which converge in Bangladesh and together with 54 smaller rivers, empty into the Bay of Bengal through a series of small rivers
How is the coast flooded in Bangladesh each year?
Almost every year, huge areas of the country flood as Himalayan snowmelt adds to monsoon rains and high tides in the Bay of Bengal.
Between May and March, violent thunderstorms produce strong southerly winds of 160kmp/h, which bring in 6 metre high waves from the Bay of Bengal to swamp coastal areas
How is human action cauisng subsidence in Bangladesh which is leading to coastal flooding?
Some of Bangladesh’s coastlines have sunk by as much as 1.5m in the last 50 years. This is partly due to isostatic readjustment , but the main reason is clearance and drainage of more than 50 islands in the Ganges-Brahmaputra river delta. These islands have been cleared to grow rice
How has the building of embankments caused increased risk of flooding?
Also, in the 60s and 70s, large earth embankments were built around these islands to protect them against tides, but this has prevented the natural deposition of sediment that used to maintain the island’s height. Now these islands are fast submerging and millions of people are at risk of flooding if the embankments give way
Where are mangrove forests found and how do they help to protect against coastal flooding?
The largest remaining tract of mangrove forest in the world is found in the Sundarbans region of Bangladesh, on the edge of the Bay of Bengal
Mangroves are essential to marine, freshwater and terrestrial biodiversity, because they stabilise coastlines against erosion, collect nutrient-rich sediment, and provide a nursery for coastal fish. They also provide shelter and protection against extreme weather events
What has been happening to mangrove forests recently? Why is this happening?
The Sundarbans forest helped to take the sting out of Cyclone Sidr in November 2007, but satellite images show that 71% of Bangladesh’s mangrove forested coastline is now retreating by as much as 200 metres a year. The main cause of this is the removal of it.
Globally, half of all mangrove forests have been lost since the mid twentieth century. Converting the forest into shrimp farms accounts for 25% of this loss
How did mangroves in the Indian Ocean tsunami protect victims compared to in an area with no mangroves?
2 people died in the settlement protected by dense mangrove forests, while up to 6000 people died in the village that had removed the vegetation
What has Sri Lanka done to protect mangrove forests?
Sri Lanka has become the first country to protect all of its mangrove forests. Its scheme will protect all 8,800 hectares of remaining forest, as well as replanting mangroves that have already been felled (and funding micro loans for villagers in exchange for them protecting local mangrove forests
What was the date of cyclone Sidr?
15th November 2007
How high was the storm surge at its biggest in 2007?
6 metres
How many people died in Cyclone Sidr?
3363
How do storm surges form?
For every drop in air pressure of 10 mb, the sea level rises by 10cm. During tropical cyclones, the air pressure may be 100mb lower than normal, which will raise the sea level by 1 metre. This rise in sea level is intensified in areas where the coastline is funnel shaped, such as at the Bay of Bengal
What are storm surges?
they are changes in sea level caused by intense low pressure systems- depressions and tropical cyclones- and high wind speeds
How fast were the winds in Cyclone Sidr
223km/hr
What category storm was Cyclone Sidr?
4
What time in the day did the eye of Sidr cross the coast near the Sundarbans’s mangrove forests?
9:30pm
What % of all recorded storm surges have happened in Bangladesh?
40%
What was the estimated cost of Cyclone Sidr?
$1.7 billion
