floodsThousands of years ago, before humans built cities and planted crops, rivers carved deep canyons and shaped continents. These rivers often overflowed and flooded the surrounding areas, depositing mineral-rich silt and soil into the surrounding plains and valleys. Because of the way floods enrich the soil, some of the first cities were built along rivers. The most important ones grew along the Indus River in Pakistan; the Nile in Egypt; the Yellow River in China; and the Tigris and Euphrates in the Middle East. These floodplain rivers are called the “cradles of civilization.” (Michael Burgan and Robin Doak) Although floods happen everywhere, there are only four types of floods. River floods occur along rivers and usually occur due to heavy rainfall over a large area. This can also be caused by melting snow and ice and can last for weeks. In most of the world, dams and levees help prevent rivers from flooding by blocking water and storing it in lakes and reservoirs. Sometimes a dam breaks, causing another type of flood. Dam failure floods occur when dams or other man-made structures are neglected, poorly designed, or damaged. These floods are very dangerous because a huge amount of water is released suddenly and without warning. Flash floods occur when a large amount of rain falls very quickly. Flash floods generally occur in mountainous areas and are so deadly because they occur with little or no warning. Coastal flooding occurs along coastlines ...