We have used the case study of the Mississippi River flood.

The Mississippi has a high flood risk because:
It has over 100 tributaries
Its drainage basin covers 1/3 of the USA and some of Canada
Heavy rain in April 1993 saturated the upper basin so storms through June and July caused a large amount of surface run-off
An area of land the size of Britain was flooded
Road bridges had to be closed
43 lives were lost and a lot of property was destroyed. There were 50,000 evacuees
Long term effects included the fact that the water didn't go away quickly and it was still draining off the land months later
Sewage had been washed into the water so there was a great risk of disease
It took months to clean out houses and offices
Stagnant water attracted mosquitoes and rats
Human activity: dams, no water could penetrate through the soil because of buildings and concrete

Reducing the risk of flooding:
Dams have been added to make large lakes
Strengthen the levees
Afforestation - trees are planted to slow down surface run-off