Whats a river basin?

A river basin has lots of streams which join to form tributaries which later join to form the main river. When it rains, most of the water slowly drains into streams, then into tributaries and finally into the main river. A river basin is an area of land drained by a main river and it's tributaries. The area of highland marking the edge of the basin is called a watershed.

Floods

A flood occurs when thre is too much water for a river to carry away in its river channel. The river overflows and covers any flat surrounding countryside.

In some places there are floods every year, but they seem to be getting worse. Te country relies on the heavy monsoon rains to flood the rice fields, but too much rain can destroy the crop as well as the homes of the farmers.

There are many causes of floods. Sometimes a flood has only one cause, often there are several reasons. As this map shows, floods can occur in different parts of the world. The examples chosen show that flooding can affect river basins, and coastal areas.

In many parts of the world floods seem to be occuring more often and they also seem to be increasing in size. This is blamed on human activity.

The reasons for tryingto reduce the risk of floods may depend upon several factors.

Places wich flood frequently are more in need than places which only flood occasionally.

Small floods may be a nuisance which have to be endured. Perhaps nothing can stop very big floods.

Attempts to stop floods will be greater where lives and property of many people are at risk.

The methods used will depend upon the wealth of a country. For example, poorer countries cannot afford expensive dams like those in U.S.A

The water cycle

The water cycle is when wateris used over and over again in a never-ending cycle. The amount of waterin the cycle always stays the same. Some of the water may be stored in the sea, in the air and on the land. Later some water will be transferred around the cycle.

Evaporation- The transfer and change of water from the ground into water vapour in the air. Water vapour is an invisible gas.

Transpiration- The transfer and change of water from plants into water vapour in the air.

Condensation-Water vapour in the air changes back into liquid. It forms small droplets which are visible as cloud.

Precipitation- The transfer of water from the air to the land. Water can fall to the earth as snow, sleet, rain or hail.

Surface water-The transfer of water back to the ground surface. It is called surface run-off. It is easiest to see where it forms rivers.

Groundwater-The transfer of water through the ground back to the sea.

Supplies of fresh water

With over 3/4 of the earth covered in water there should be plenty for plants, animals and people. Unfortunately over 97% of that water is in the seas and oceans. As this is salt water cannot be used by life on land. To make matters worse, 3/4 of the fresh water is held in storage as ice or snow. This water can only become available if the worlds glaciers and iceceaps melt.

Water transferred

Although in Britain we get far more rain than we need it does not always fall where it is needed.The supply falls in the mountainous parts of north and west Britain where fewer people live.The biggest needed the demand is in the flatter south and east where most people live. Therefore water is stored in those areas with largest supply and transferred to those areas with biggest demand.

The Amazon

From the Andes to the atlantic ocean, the Amazon recovers 6470 kilometers through a landscape without horizon. Because inside the jungle, the worlds langth are only thusands of metres. Along, a big wall of plants doesnt live people go throgh that huge world. The light can't go through and theres nearly no air. Plants and animals are here the kings. In the jungle theres a territory were a river floods the area with huge rocks and with huge descending parts. during the floods in may and october you can only see the top part of the trees, one of the most common animals that live in the amazon river, are the crocodrile, they eat little fishes or someones that are little but,they are little beasts.The river amazon is an oportunity for seing the natural things.

The amzon was discovered by Amerigo vespucci in1499 and explored by Vicente Yañez Pinzon in 1500. The 1542 the expedicion of Francisco de Orellana sailed from the river Coca aswell to the mouth, and the 1632 misioners did the same.

A river

The rivers make the land higher, smaller and wider, there are 3 processes :

Erosion, transport and sedimentation, A small river runs very quickly so that it produces erousions, going down, the river makes a small valley.

(1) When the river gets bigger it gets things on the way and they let them infront, it produce an erosion making a bigger valley

(2) On its last fase, the river makes some deltas.

The river is made on the mountains , when there is a lot of rain the river is made or the river is filled, when the river is filled it goes quicker and floods occur, the river gets bigger.

The more important rivers in the world

Volga 3,690

Danube 2,900

Ural 2,428

yangtse kiang 5,500

Huang Ho 4,845

Mekong 4,500

Nile 6,671

Zaire 4,374

Niger 4,184

Amazon 6,437

Mississippi-Missouri 6,180