page_title: Valley
section_title: River valleys
hierarchical_section_title: Valley / River valleys
caption_attribution_description: Български: Защитена зона Палакария – долината между Витоша и Рила. На преден план – село Белчин English: Protected locality Palakaria in Bulgaria – the valley between mountain Vitosha and Rila. To the front: village of Belchin This is a photo of a natural heritage site in Bulgaria, id: ZZ2084
context_page_description: A valley is a low area between hills or mountains typically with a river running through it. In geology, a valley or dale is a depression that is longer than it is wide. The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys. Most valleys belong to one of these two main types or a mixture of them, at least with respect to the cross section of the slopes or hillsides.
context_section_description: A valley formed by flowing water, called fluvial valley or river valley, is usually V-shaped. The exact shape will depend on the characteristics of the stream flowing through it. Rivers with steep gradients, as in mountain ranges, produce steep walls and a bottom. Shallower slopes may produce broader and gentler valleys. However, in the lowest stretch of a river, where it approaches its base level, it begins to deposit sediment and the valley bottom becomes a floodplain.
  Some broad V examples are:
  North America: Black Canyon of the Gunnison National Park, and others in Grand Canyon NP
  Europe:
  Austria: narrow passages of upper Inn valley (Inntal), affluents of Enns
  Switzerland: Napf region, Zurich Oberland, Engadin
  Germany: affluents to the middle reaches of Rhine and Mosel
  Some of the first human complex societies originated in river valleys, such as that of the Nile, Tigris-Euphrates, Indus, Ganges, Yangtze, Yellow River, Mississippi, and arguably Amazon. In prehistory, the rivers were used as a source of fresh water and food (fish and game), as well as a place to wash and a sewer. The proximity of water moderated temperature extremes and provided a source for irrigation, stimulating the development of agriculture. Most of the first civilizations developed from these river valley communities.
caption: Valley of Palakaria river springing from Vitosha Mountain, seen in the background, in Bulgaria
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