The ground below the water table (the blue area), is saturated, whereas the ground above (the gray area) is not. Groundwater seepage can sometimes be seen when water-bearing layers emerge on the land surface, or even on a driveway! If a river bank happens to cut into this saturated layer, as most rivers do, then water will seep out of the ground into the river. At a certain depth below the land surface, called the water table, the ground becomes saturated with water. Rain falling on the land also seeps into the Earth to form groundwater. It is also true that most of the water flowing in rivers comes from precipitation runoff from the surrounding landscape (watershed).īut, the water in a river doesn't all come from surface runoff. The most simplistic answer is that all the water in a river comes from the sky-and that is certainly true, as streamflow is one part of the water cycle. The mighty river featured in this image is called the Yarlung Tsangpo as it courses through the Tibetan Autonomous Region of China. Large rivers don't start off large at all, but are the result of much smaller tributaries, creeks, and streams combining, just as tiny capillaries in your body merge to form larger blood-carrying arteries and veins. If people have built a dam to hinder a river's flow, the lake that forms is a reservoir. If water flows to a place that is surrounded by higher land on all sides, a lake will form. Rivers eventually end up flowing into the oceans. As small creeks flow downhill they merge to form larger streams and rivers. Flowing water finds its way downhill initially as small creeks. In most landscapes the land is not perfectly flat-it slopes downhill in some direction. ![]() When rain falls on the land, it either seeps into the ground or becomes runoff, which flows downhill into rivers and lakes, on its journey towards the seas. Most, but not all, precipitation that falls in a watershed runs off directly into rivers - part of it soaks into the ground to recharge groundwater aquifers, some of which can then seep back into riverbeds.Ī river forms from water moving from a higher elevation to a lower elevation, all due to gravity. The area of land between ridges that collects precipitation is a watershed or drainage basin. Rivers flow through valleys in the landscape with ridges of higher land separating the valleys. Some of it evaporates on the journey downslope, can be diverted and used by people for their uses, and can even be lapped up by thirsty animals. Of course, not all runoff ends up in rivers. Most of the water you see flowing in rivers comes from precipitation runoff from the land surface alongside the river. I tend to think of creeks as the smallest of the three, with streams being in the middle, and rivers being the largest. As far as our Water Science site is concerned, they are pretty much interchangeable. Rivers? Streams? Creeks? They are all names for water flowing on the Earth's surface. ![]() Bow River Falls, downstream from the Bow Glacier in Banff, Canada. Glacier melting in springtime causes high streamflows. Sources/Usage: Some content may have restrictions.
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