Managing the Physical Environment

Weather Hazards

What problems does flooding cause?

What are the effects of flooding?

Primary• Loss of life• Injury• Loss of land/buildings• Industry/

communications destroyed

Secondary• Loss of shelter• Limited food supply• Contaminated

water/disease• Loss of employment/

income

To what extent is flooding a natural hazard?

Natural Factors• High rainfall• Higher

temperatures causing snow melt

• Low pressure storms

• High tides and on-shore winds

Human Factors

• Changing slopes

• Removing vegetation

• Changing river patterns/ flows

• Building on flat land near rivers

Global warming could increase the risk of coastal flooding if sea-levels rise.

Case Study: Bangladesh (LEDC)

Bangladesh is a country that has both river and coastal floods.

River Floods – result from heavy rainfall and melting show in the Himalayas. Farmers rely on the floods to supply fine silt to the land, making it fertile and good for growing crops.

Coastal Floods – are created by cyclones which push the water in the Bay of Bengal towards the land, causing a storm surge. This flood the low-lying coastal areas.

Case Study: Bangladesh (LEDC)

Bangladesh is a country that has both river and coastal floods.

Case Study: Bangladesh (LEDC)

Can Bangladesh be protected against flooding?

Case Study: Bangladesh (LEDC)

How well has the scheme worked?

Advantages• Flood embankment in Dhaka

appears to reduce the effects of flooding

• Flood warning systems gives people time to prepare

• People are more educated about what to do in a flood

• A number of shelters have been built

• The building of embankments has created jobs

Disadvantages• At £100 million a year,

maintenance costs are high for a LEDC

• Pumping systems do not always separate floodwater from sewage = disease

• Embankments create pools of stagnant water which attract mosquitoes = disease

• The pattern of flooding has changed this affects the farming and fishing communities

Case Study: Mississippi (MEDC) In the summer of 1993, the Mississippi River in the USA burst its banks.

Causes• The Mississippi drains over

30% of the USA• Continuous rainfall from April

to July saturating soils leading to rapid overland flow

• Heavy thunderstorms in June delivered record rainfall

• The river is fed by over 100 tributaries

Effects• Levees collapsed• 9000 homes destroyed• 70,000 evacuated• 48 people killed• St Louis no water or power

supplies• One million acres of crops ruined• Roads, railways and bridges cut

off• Sewage contaminated water• Sedimentation blocked channels,

disrupting shipping

• The Mississippi is a vital transport route running from north to south in the centre of the USA. Engineers have had to work to maintain a channel of water deep enough for river traffic and to control the river's regular floods, protecting settlements and farmland throughout the river basin.

• Engineers have altered the Mississippi in the following ways:– 'Wing dykes' have been built to slow down the river on one side

whilst speeding it up on the other, creating a deeper channel for navigation.

– Sections of the river have been straightened by cutting through meanders. The river is now 150 miles shorter.

– 1600 kms of levees (embankments) have been built to prevent the river spilling over the flood plain.

– Many dams and reservoirs have been built on tributaries to hold back and store water.

– Much of the river has been lined with concrete slabs.

Case Study: Mississippi (MEDC)How was the Mississippi managed?

• Despite control methods the flood of 1993 was the worst ever. Engineers called it a 'one in a hundred' flood caused by exceptionally heavy rainfall.

• Many environmentalists argue that far from controlling the Mississippi, the engineers' efforts have made things worse by:– shortening the river, causing it to flow more quickly and

increasing erosion. – restricting the flow of water inside levees, speeding up the flow

and increasing the pressure on the levees and the likelihood of flooding. In 1993 a large number of levees broke or were too low to stop flooding.

– altering the natural flow of the river to such an extent that the 1993 floods were the worst ever, even though there was less water in the river than during previous major floods.

– increasing the energy in the river, because there is less sediment being moved around.

Case Study: Mississippi (MEDC)Did engineers cause these floods?