Hwa Chong Institution
Secondary 2 Geography 2015
Revision Exercise 4: Floods
Name: ……………………………………….. (
)
Date:………………
Class: ………
1.
Fig. 1 is an article on destruction of the mangrove forest in Jakarta, the
capital city of Indonesia.
(a) Explain the natural and human factors which have led to increased risk [5]
of flooding in the area.
Natural
 Indonesia is having its rainy season/ monsoon season
 City may face higher rainfall intensity and duration
Human
 destruction of the mangrove forest to build the airport road is likely
to increase the risk of flooding to the area.
 Forest will no longer intercept rainfall;
 Soil will be compacted/easily saturated;
 Forest is replaced with tarmac;
 which is impermeable and water is unable to infiltrate into the
ground
 More surface runoff will take place…thus increasing the risk of
flooding
 Coastal areas are susceptible to coastal floods as
 Mangroves protect coastal areas from storm surges caused by
typhoons or hurricanes
(b) Explain why, in many developing countries, large number of people
live close to rivers which may flood.
 Availability of flat land;
 ease of communications using river;
 flat land for growing crops;
 water for irrigation;
 water supplies for domestic use/river for washing;
 fishing in river/food supplies;
[3]
(c) For a named river which you have studied, explain what has been
done to reduce flooding.
[3]
Answers may include regulation
 Zoning is a way which the government plans the physical
development of the land and its uses
 Flood prone areas are often zoned as low-value developments
such as parks and fields for recreational activities
 With the use of zoning, cities are likely to suffer fewer economic
losses in the event of floods
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
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For eg, in Minnesota, USA
Areas prone to floods near the Minnesota river are used for low
value developments such as the Minnesota Valley National Wildlife
Refuge and parks
Beyond the zone of low value developments is the industrial areas
Residential zones are located furthest away from the river so that
houses may be safe from floods
Or investment in infrastructure
 levees and floodwalls are barriers against floods and protect the
development against floodwater
 Levees are raised river banks which can be natural or man-made
 Floodwalls are man-made structures made of concrete
 Both structures are built higher than the floodplains and rivers so
that they can keep out floodwater
 For example, in the city of Sacramento, USA, the Sacramento
River flows south and drains into the San Francisco Bay
 Since 1970s, several kilometres of levees have been built along
the river to protect the surrounding land from floods