Rivers eventually end up flowing into the oceans. If water flows to a place that is surrounded by higher land on all sides, a lake will form. If people have built a dam to hinder a river's flow, the lake that forms is a reservoir. The river serves many purposes, from drinking water to wildlife habitat to a recreation spot for the whole city. The phrase "river of life" is not just a random set of words.
Rivers have been essential not only to humans, but to all life on earth, ever since life began. Plants and animals grow and congregate around rivers simply because water is so essential to all life.
It might seem that rivers happen to run through many cities in the world, but it is not that the rivers go through the city, but rather that the city was built and grew up around the river. For humans, rivers are diverted for flood control, irrigation , power generation , public and municipal uses, and even waste disposal.
Are rivers one of your favorite places? If so or if not, why not vote for your favorite water body in our Activity Center! 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. The mighty river featured in this image is called the Yarlung Tsangpo as it courses through the Tibetan Autonomous Region of China.
Credit : NASA. 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. It is also true that most of the water flowing in rivers comes from precipitation runoff from the surrounding landscape watershed. But, the water in a river doesn't all come from surface runoff.
Rain falling on the land also seeps into the Earth to form groundwater. At a certain depth below the land surface, called the water table , the ground becomes saturated with water.
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. Groundwater seepage can sometimes be seen when water-bearing layers emerge on the land surface , or even on a driveway! Look at the diagram below. The ground below the water table the blue area , is saturated, whereas the ground above the gray area is not.
Saturated, water-bearing materials often exist in horizontal layers beneath the land surface. Since rivers, in time, may cut vertically into the ground as they flow, the water-bearing layers of rock can become exposed on the river banks.
Thus, some of the water in rivers is attributed to flow coming out of the banks. This is why even during droughts there is usually some water in streams. In the diagram you can see how the ground below the water table the blue area is saturated with water. The "unsaturated zone" above the water table the gray area still contains water after all, plants' roots live in this area , but it is not totally saturated with water. You can see this in the two drawings at the bottom of the diagram, which show a close-up of how water is stored in-between underground rock particles.
Like everything else on and in the Earth, water obeys the rules of gravity and tries to get to the center of the Earth did you imagine that every molecule in your body is trying to do this, also? So, the water in rivers flows downhill, with the ultimate goal of flowing into the oceans, which are at sea level. This data set is the first of its kind to do this at a global scale on high resolution. Plus, now that this fine-tuned, river-measuring technique has some reliable results, he said it could be useful to see how river flow rates change from season to season—another good data set to have when working to keep communities safe from floods.
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