Geologists divide landscapes into their different drainage basins. Other names for a basin are watershed or catchment. All precipitation in a catchment drains into the same stream. There are drainage divides that separate one basin or catchment from another. As streams travel further, they come together to make rivers that drain as tributaries into other rivers. Finally, all rivers or continental waters from them will end up in a larger area, such as an ocean. Figure 58 depicts a basin and its main features: Streams start as headwaters. These are often small tributaries or branches of larger streams or rivers to make a trunk stream. The mouth of the stream is where it ends and discharges its contents into something else. Two equal streams meet at a confluence. Many streams and rivers have a mouth in the ocean, which is where fresh water meets ocean water. Some do not ever reach the ocean. What then? These are closed basins or endorheic basins that end in a lake that just evaporates over time. The Great Salt Lake in Utah is an endorheic basin lake. You can describe basins in several ways. A basin is also what we call the entirety of land that drains into the endpoint, which is usually the ocean. Most of the Midwest and some of the eastern parts of the US are of the same basin. The west and part of the east are in their own basins. The Great Salt Lake area and several others in Eurasia and parts of Africa have their own endorheic basins.
SURFACE WATER EXPLAINED Streams are flowing bodies of water. In geology, the terms brook, creek, and river are not used. Everything is a stream. Streams cause a great deal of erosion all the time and send sediment downstream toward the oceans. There are two factors that affect the degree of erosion. The first is the velocity of the stream's water. How fast is it going? Second, you want to know the channel gradient, which is how downsloping the water is. It is measured in terms like feet per mile or meters per kilometer. A taller mountain with a stream probably has a larger channel gradient. Erosion of a stream leads to a valley over time. The wider the valley, the larger was a given stream at one point – even if it is narrow in the present time. The velocity or water speed you see in a stream depends on several factors. The channel gradient, the
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