Chong Boon Secondary School

Sec 2 Geography

FloodsUnit 5 Lesson 2

Cities prone to floods

Inquiry Question Why are some

areas more prone to floods?

Flood Occurrence 1985-2011

Key reasons for bigger flood risk

• Larger amount of rainfall received.

• Height of land above sea level.

• Presence of flood protection measures.

Heavy Rainfall

• Dhaka, Bangladesh

• Located in monsoon paths

• Seasonal rains (monsoons)

–Intense and prolonged.

• New Orleans, USA

• Along Hurricane belts

–Intense and strong rains.

Snowmelt

• Calgary, Canada

• At the foothills of mountains.

• Spring snowmelt leads to sudden, massive increase in river load.

Storm Surges

•Coastal countries (Philippines)–Storm surges due to weather

–Typhoon Haiyan (Tacloban)

–Massive destruction

Video courtesy of Plan Internationalhttps://www.youtube.com/watch?v=XUZFW54vtDo

Danger of Dam failure

• Rio Largo, Brazil

• Prone to floods due to location near dams

• Risk of dam failure

Dam Failure

Height of land above sea level

• Sea level refer to mean sea level

–Average height of the sea at a given site over a period of time.

–Mid point between the mean low tide and mean high tide.

Height of land above sea level

• Cities located on low-lying lands (below sea level) are more prone to floods.

• Amsterdam, Rotterdam, Venice

Proximity to water bodies

• Oceans, seas, lakes, reservoirs.

• Cities near such places run higher risk of flooding.

• Event of sudden increase in water amount in the water bodies lead to immediate flooding.

Pg 167

Permeability of surface cover

• Permeability

–Ease with which water can infiltrate or seep into the ground.

• Vegetated surfaces more permeable

• Concrete surfaces hare impermeable

• Lower permeability leads to higher flood risk.

Channel Capacity

• Volume of water held in the channel of a river without overflowing.

• Sudden increase in water lead to overflowing.

• City’s drainage system needs constant upgrading to increase the capacity.

Pg 169

PUB’s flood response

• Canals deepening and widening

–Rochor Canal and Alexandra Canal

• Construction of additional canals and drains

• Raising road heightsPg 170

What’s protecting Bangkok?

Summary

• Why do some cities flood easily?

• What are some measures Singapore has taken to cope?

“Good or Bad?”

There are 6 factors shown in the sketch below. In your groups,

briefly (in no less than 3 sentences) explain how each factor canaffect (increase / decrease) the area’s flood risk.Answer on the A3 paper provided.

Let’s pick 3 groups to present!