What Causes a Flood? Floods are one of the most common disasters in the United States.Flood effects can be local, impacting a neighbourhood or community, or very large, affecting several states. __ 1 __ Some floods develop slowly, sometimes over a period of days.But flash floods can develop quickly, sometimes in just a few minutes and without any visible( 看得见的 ) signs of rain.Flash floods often have a dangerous wall of roaring water and can take away most things in its path. Floods happen when a watercourse( 水道 )overflows.__ 2 __ Heavy rain When the ground already contains a lot of water, the falling rain could not seep through it.The water then starts flowing toward a watercourse.When it rains a lot in a region, all water flows toward the river, but this river can not contain it.__ 3 __ Thaw When spring arrives , snow and ice start to melt and the water flows toward the river.__ 4 __ The river overflows and a flood happens. Ice jam In spring, rivers thaw out and pieces of ice drift on the river.__ 5 __As a result, these pieces of ice form a kind of dam( 水坝 ) . When water cannot flow through this dam, it tries to find another course to reach the river and sometimes, this new course is a field, a road or a house basement. A . We can think of some ways to prevent the flood from happening. B . However, all floods are not alike. C . Therefore, the river overflows. D . Sometimes these ice pieces get jammed against a bridge or rocks. E . They could be caused by heavy rain, thaws( 解冻 ) or ice jams( ) . F . One of the biggest problems people faced was lack of fresh water. G . If the temperature rises too rapidly, a lot of water is produced in a short time.