在自然灾害面前，我们的力量是微小的，也是强大的。微小是因为自然强大的力量， 强大是我们坚强的生存。北京新航道小编整理了一篇托福阅读背景材料，供大家参考学习。

　　Over half of the world is covered with water, we need it to stay alive. When there's too much water, or water in the wrong place, it's a problem we call flooding.

　　In the UK people are sometimes forced out of their homes when lots of rain has fallen in a short space of time and caused a flood.

　　What is a flash flood?

　　It's where a river's level rises very fast, the flood may arrive instantly in the form of a wave or wall of water. People have no time to get to the safety of higher ground.

　　Flash floods are unusual in the UK, we do get a lot of rain and sometimes it's really heavy but normally the soil and plants act like a giant sponge. They soak up the rainwater and slow it down on its journey into our rivers.

　　Sometimes the sponge effect doesn't work because the ground is already very wet. When that happens all the rain tries to get into the river at the same time. If the river isn't big enough to handle the water there will be a flood.

　　Flat area

　　In a flat area the rainwater sits around in temporary ponds and lakes until there is room for it to get into the river, it's like a rainfall traffic jam.

　　Hilly area

　　Where the ground is steep you could be looking at a dangerous flash flood. Gravity pushes all the rainwater into the river at the same time. The river level rises really quickly, and the water moves downhill fast. As it travels it picks up objects in its path. They might be cars, trees or even giant boulders.

　　Steep narrow valleys are the most at risk, a lot of water is trying to push through a small gap. This causes a 'bottleneck' and makes the flooded river even deeper.

　　Rivers are formed over a large number of years by the movement of water over and through land.

　　The river forms so that the water will have somewhere to go.

　　Floods happen when more water tries to fit into a river than there is space for. The river bursts its banks.

　　The ground in different bits of the country is made up of different types of soil and rock.

　　Some combinations are able to soak up more water than others.

　　If a place that cannot soak up much water is rained on heavily, there is nowhere for the water to go and flooding happens.

　　The ground can only soak up so much water, to a level called the water table. The water table is higher in certain areas of the country, making those locations much more at risk.

　　以上就是托福阅读背景材料中有关洪水相关的信息，有关自然灾害的信息，我们时刻关注，至少在考试中不陌生。北京新航道小编预祝各位考试顺利，取得优异的成绩。

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