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Rapids cause water aeration of the stream or river, resulting in better water quality. [2] For a rapid to form, a necessary condition is the presence of a gradient, which refers to the river or stream's downward slope. When a river has a larger gradient, the water flows downhill faster. [3] Gradients are typically measured in feet per mile. [4]
The international scale of river difficulty is an American system used to rate the difficulty of navigating a stretch of river, or a single (sometimes whitewater) rapid. [1] The scale was created by the American Whitewater Association to evaluate rivers throughout the world, hence international in the title. [ 2 ]
The average flow rate at the mouth of the Amazon is sufficient to fill more than 83 such pools each second. The estimated global total for all rivers is 1.2 × 10 6 m 3 /s (43 million cu ft/s), [ 1 ] of which the Amazon would be approximately 18%.
All rivers with average discharge more than 15,000 cubic feet per second are listed. Estimates are approximate, because data are variable with time period measured and also because many rivers lack a gauging station near their point of outflow.
Rivers flow downhill, with their direction determined by gravity. [6] A common misconception holds that all or most rivers flow from North to South, but this is not true. [6] As rivers flow downstream, they eventually merge to form larger rivers. A river that feeds into another is a tributary, and the place they meet is a confluence. [4]
A marked increase or decrease in flow can create a rapid, "wash out" a rapid (decreasing the hazard), or make safe passage through previously navigable rapids more difficult or impossible. Flow rate is measured in volume per unit of time. The stream flow rate may be faster for different parts of a river, such as if there's an undercurrent. [2]
The project will remove four dams on the Klamath River. The project is part of a larger trend across the U.S. to remove dams blocking the natural flow of rivers and streams.
Mile 44.0 – President Harding Rapid (4) – The river splits around a large rock in the middle of the river. Mile 52.4 – Nankoweap Rapid (3) Ancestral Puebloan granaries at Nankoweap Creek (Mile 52.4) There are three popular campsites at Nankoweap for river trips. A steep trail up a nearby talus slope leads to Ancestral Puebloan granaries.