- Rivers can be straightened
- If there are levees they can be raised higher
- Dredging river beds (removing sediment and silt)
- Building dams and reservoirs
- Planting more trees
Case Study 1
MEDC: New Orleans (Hurricane Katrina) Flood 2005
Like many costal and river delta cities New Orleans had been vulnerable to flooding in the past, but when Hurricane Katrina struck on August 29th to September 1st 2005 most of New Orleans was left under water and the whole city was in complete chaos.
Nearing the end of August most residents had evacuated as Katrina was fast approaching.
The day before Katrina hit, high tides created by the storm’s outer bands already engulfed low-lying wet lands and communities outside the levee system.
Time-line of events
4:30 am: in the Industrial Canal the rising water leaks through damaged gates into neighbourhoods of both sides of the 1-10 High rise.
5 am: Hurricane Katrina creates a storm surge that begins pounding the MR-Go levee. By dawn levee sections crumble and lake Borgne advances into wetlands toward St.Bernard.
6:10 am: Katrina makes landfall at Buras. A wall of water 21 feet high crosses the Mississippi river. And its levees, inundating most of Plaquemines.
6:30 am: The surge builds in the Intracostal waterway’s “funnel,” and levees protecting eastern New Orleans are overtopped. The area is quickly submerged with water.
To the west, witnesses report sections of the 17th street Canal levee wall are leaning toward Lakeview. Water seeps through cracks in the wall into the neighbourhood.
6:50 am: Storm surge from the “funnel” reaches the Industrial Canal. Water overtops floodwalls and levees on both sides, but the worst is still to come.
7:30 am: On the west side of the Industrial Canal Levee wall panels open, flooding the upper 9th Ward, Bywater and Treme.
7:45 am: Two floodwall sections on the east side of the Industrial Canal fall, releasing a wall of water into the lower 9th Ward, crashing down on homes and cars. The water also pours into Arabi and Chalmette.
8:30 am: In Lake Borgne water rises and easily tops over at St.Bernard’s 7-foot to 9-foot 40 Arpent Canal levee, filling neighbourhoods from Poydras to Chalmette.
North, a one-mile stretch of floodwall on the south side of Lakefront Airport is topped by surge from Lake Pontchartrain, adding to already severe flooding in eastern New Orleans.
9:00 am: The Surge rises to 10 feet in the London Avenue Canal, its levee’s wall panels start bending, water leaks into yards.
Roughly two miles west the water reaches an embankment at the foot of Orleans Avenue Canal. It is 6 feet lower than the floodwalls. Water tips over and rushes into the City Park.
9:30 am: 1-wall panels on the east side of London Avenue Canal fail, releasing a wall of water and sand into homes and expanding the flooding of Gentilly.
9:45 am: Several 17th street Canal levee wall panels fail, releasing a rush of water into Lakeview. Water from this eventually fills much of midtown New Orleans and parts of Metairie.
On the north shore, Katrina made landfall near Slidell. A 15-foot storm surge at the Lake Pontchartrain shoreline reaches more than 5 miles inland at some points. St. Tammany neighbourhoods from the Rigolets all the way to Madisonville are flooded.
10:30 am: Wall panels on the west side of London Avenue Canal are pushed over, adding 8 feet of water to already flooded Gentilly and contributing to the rising water across the city.
Parts of Jefferson also flood as rainwater leaks through an empty staffed pumping system.
With Katrina moving quickly toward north of the city, surge levels dropped and water ceased to top over the levees. However Lake Pontchartrain now covers a larger area than before and water continued flowing into the city until the lake level equalises with the floodwaters at midday on September 1st.
Short Term Effects
- Storm surge produced by the hurricane caused the city to suffer the worst civil engineering disaster in American history.
- Levees that were constructed by the U.S. Army Corps of Engineers had failed, leaving 80% of the city flooded.
- More than 10,000 of remaining residents were eventually rescued by helicopter or took shelter at the Louisiana Superdome or the Morial Convention Centre.
- Over 1,500 people died.
- The event disrupted power, natural gas, water, sewage, road safety and other essential services to the city.
Long Term Effects
- The city was declared off-limits to residents while clean-up efforts began. The approach of Hurricane Rita caused repopulation efforts to be postponed and the Lower Ninth Ward was reflooded by Rita's storm surge. By October 1, parts of the city accounting for about one-third of the population of New Orleans had been reopened.
Case Study 2
LEDC: Bangladesh Flood 1998
Bangladesh is well know for flooding as Since July to mid-September in 1998 Heavy Monsoon rain had contributed to a large amount of flooding in many areas of Bangladesh.
Causes
- Heavy Monsoon rain causes summer flooding
- Snow melting in the Himalayas melting adds to level of water.
- Deforestation means fewer trees to absorb water and so can move more freely to the lower lands of Bangladesh.
- 80% of Bangladesh is a floodplain and delta making it prone to flooding
- Because the river Brahmaputra and the river Ganges meet it increases the flood risk.
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An increased surface run-off results in soil erosion and more silt being built up in river beds (Brahmaputra river bed rising)
- A total of 70 per cent land area is less than 1m above sea level.
Effects
- Over 57 per cent of the land area was flooded.
- In the north-east of Assam more than 1 million people lost their homes.
- 240 villages were submerged in the Nalbari district.
- More than 1000 people were killed and millions were made homeless.
- There were severe shortages of drinking water.
- Diseases such as bronchitis and diarrhoea spread.
- The Floods damaged fields (crops), buried villages in sand and silt and wrecked roads and bridges.
- The floods cost the country almost $1 billion worth in damages.
Short Term Relief
- Farmers were provided with free seed from the government
- Foreign aid (including 21 million from the UK government) and food aid was given.
- Water Purification tablets were brought by money raised by the WHO (World Health Organisation)
Long Term Flood Protection Measures
- Flood protection shelters built, which can provide shelter in times of floods. Although can be swept away by them also.
- Flood embankments built along the river. (7 500km built since 1947)
- Upstream dams suggested. These would hold back the flow at its peak, but the costs of construction are very high.
- Reduce deforestation in main water areas.
- Providing emergency flood warning systems to give warnings and organise rescue and relief services (emergency medical and food supplies).