sentence: Some valleys are almost flat, like a large saucer.
sentences_after: The 'tributaries' carry water from the hills or mountains that may be far from the main river. After heavy rain, lots of water rushes into the main river so that it rises and floods over the flat floor of the valley. When the flood waters spread, they drop lots of soil which has washed down from the hills. The soil that drops on the valley floor makes the valley flatter. Valleys of this type are very useful for growing food crops.
concept_name: valley
headings: Valley Types of valleys Valleys in flat country