YEAR 10 GEOGRAPHYRIVERS AND WATER8. RIVERS AND FLOODING

RIVER FLOODSA river floods when the water normally flowing in the channel overflows its banks and spreads out onto the surrounding land. This causes major problems for people living close to the river.

FACTORS TO INCREASE FLOODINGA variety of factors can increase the likelihood of flooding.

Physical causes of flooding:• heavy rainfall• long periods of rain• snowmelt• steep slopes• impermeable rock (doesn't allow water through)• very wet, saturated soils• compacted or dry soil

HUMAN FACTORSHuman factors increasing flood risk:• urbanisation, because towns and cities have more

impermeable surfaces• deforestation, because removing trees reduces the

amount of water intercepted and increases run-off

STORM HYDROGRAPHSA storm hydrograph is a graph to show how and when a rainfall event affects the discharge of a river.

OTHER FACTORSThe amount and intensity of the rainfall is not the only factor influencing the shape of the hydrograph. There are other influences.

CASE STUDY: BOSCASTLE 2004Boscastle is a small coastal settlement in the south west of England. It flooded in August 2004, washing cars and buildings into the sea and putting peoples' lives in danger.

CAUSES OF FLOODINGHeavy localised rainfall - 89 mm of rain fell in an hour.Saturated ground from previous rainfall.Topography of the land. The landscape upstream of Boscastle, a steep-sided valley, acted as a funnel directing vast volumes of water into the village.Narrow river channels in the village itself.

PREVENTION OF FLOODING£4.5 million has been spent on a flood defence scheme.The scheme stretches along the valley, incorporating drainage, sewerage systems and land re-grading.Boscastle car park has been raised in height, which will stop the river from bursting its banks so easily.New drains allow water to run into the lower section of the river quickly.The river channel has been made deeper and wider so that it can accommodate more water.

CASE STUDY: BANGLADESH 2007Bangladesh is a developing country in Asia and it is frequently affected by flooding. For example, in 2007 flooding made 9 million people homeless and approximately 1,000 people died from drowning and from waterborne diseases.

CAUSES OF FLOODINGCyclones cause coastal flooding.Lots of low-lying land.Melt water from the Himalayas.Heavy deforestation.Heavy monsoon rains.Increasing urban areas.

INSURANCE AGAINST FLOODINGBangladesh is a very poor country and so has less money to spend on flood defences than richer countries. Most people in Bangladesh do not earn enough to pay for insurance against flooding, so when there are floods they risk losing everything.

SHORT-TERM RESPONSESFood aid from the Government and other countries.Water purification tablets.People repaired embankments and helped to rescue people.Free seed given to farmers.

LONG-TERM RESPONSESBuilding embankments.Building raised flood shelters.Introducing flood warning systems.Emergency planning.Dams planned.Reducing deforestation.Unfortunately, many of these long-term responses are difficult to pay for and maintain. They are not always successful and don't always help enough people.

THE RED MUD IN HUNGARY 2010In October 2010, a large river of toxic red mud flowed through areas of Hungary. The mudflow was two metres high and covered an area 40 sq km. One million cubic metres of industrial waste was released into the area.

CAUSE OF DISASTERThe dam collapsed because of high rainfall.The reservoir contained industrial waste material stored from a nearby bauxite factory.The factory producing the waste may not have been properly maintained.

IMPACTS FROM DISASTERNine people died, 120 were injured.The chemicals released into the water killed fish and other wildlife.The pH level of the mud was high enough to cause chemical burns.Seven towns and around 7,000 people were affected.The topsoil in agricultural areas was left contaminated.