CAUSES OF FLOODING
Natural causes of floods:
Heavy rainfall raises the water level.When the water level is higher than the river bank or the
dams,the water comes out from the river,there will have a flooding.
Because of the golbal warming,the temperature of this year is higher than the temperature of many
years ago.The ice caps melt in spring,many water go into the sea.The water raises the sea level,and
makes the river level raise.When river level raises,flooding may cause.
Flooding often occurs in lowland.This is because rivers flow more slowly in low-lying area.If the
water volume increases suddenly,floods occur.
Flooding always occur in coastal areas.Because there have high tides or storms,the sea level will
raise.If the sea level is higher than the level of the coastal lowland,flooding will occur.
Human causes of floods:
Large areas of forests near the rivers have been cleared.The lands use to make.room for
settlement,roads and farmland.Less vegetation protect the soil,the soil is quickly lost to rivers and
sea.This raises the river bed,so the river overflows its banks easily.Deforested area.People want
more wood to build house.So,they cut many trees.Some of the Chang Jiang's near areas are
How derorestation lead to flooding:
No trees to soak up water,so more water flows into the rivers.No trees to build the soil together,so
soil erosion takes place.Large amounts of soil are washed by rain into the rivers.
Because of silting,riverbed shallower.The water volume increases,the river cannot hold all the water
and overflows its banks.
Some farming practices can damage the vegetation cover,so the soil will be washed into the river
People want more food and money,they graze too many animals on the land and the pasture
is eaten away quickly.Less vegetation cover,soil washed into the rivers easily.The areas near
Chang Jiang graze many animals.
When a piece of land has been used for farming for a long period of time,the soil may
became so infertile that no vegetation can grow on itThe land less fertile than before,so the
soil washed into the rivers more easily.
3.Poor water management
When the dams are poorly constructed or maintained ,they can easily collapse and this results in
flooding.In China,many lakes along the major rivers have been heavily silted and reclaimed,for
Example,Dongting Hu along the Chang Jiang.People want more land to farming.They reclaim the
lake,it reduces the size of the lake,it may causes flooding easily. Decreasing size of Dongting Hu ,
Because of large amount of people,everything need more,like wood,land and food Soil erosion
happen more often,it increases the risk of flooding.Large number of people live in areas with high
risk of flooding in China.They cause the problems below.Such as overgrazing and overcultivation.