Most of the water you see flowing in rivers comes from precipitation runoff from the land surface alongside the river.
Of course, not all runoff ends up in rivers. 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. Rivers flow through valleys in the landscape with ridges of higher land separating the valleys.
The area of land between ridges that collects precipitation is a watershed or drainage basin. 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. A river forms from water moving from a higher elevation to a lower elevation, all due to gravity.
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. In most landscapes the land is not perfectly flat—it slopes downhill in some direction. Flowing water finds its way downhill initially as small creeks.
As small creeks flow downhill they merge to form larger streams and rivers. 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. Natural floods can also keep invasive species in check and give important cues to fish that swim upstream to spawn. When we protect a wild river we give it room to move, and room to accommodate floodwaters safely. Wild rivers are fun—and fun can be lucrative.
Rafting, fishing, swimming, hiking and wildlife watching all draw people—and therefore money—to areas with healthy rivers.
Sometimes those are rural areas with little else to rely on for economic development. River recreation brings jobs into areas that might otherwise turn to less sustainable industries to support their economies. Visitors rent kayaks, buy gas, eat in restaurants and stay in hotels, which all adds up to cash flowing into the community. Watersports directly support more than , jobs annually.
Countless species of fish, birds and other animals live in and along rivers and depend on them for their food. What happens in the headwaters is very important to the health of the whole river, because anything that happens upstream affects everything downstream.
The shape of a river channel depends on how much water has been flowing in it for how long, over what kinds of soil or rock, and through what vegetation. There are many different kinds of river channels — some are wide and constantly changing, some crisscross like a braid, and others stay in one main channel between steep banks. Each kind of river channel has unique benefits to the environment.
In the West, these riverside areas provide habitat for more bird species than all other vegetation combined. These areas also provide valuable services like protection from erosion during floods , and filtering polluted run-off from cities and farms.
Floodplains are low, flat areas next to rivers, lakes and coastal waters that periodically flood when the water is high. The animals and plants that live in a floodplain often need floods to survive and reproduce.
Healthy floodplains benefit communities by absorbing floodwaters that would otherwise rush downstream, threatening people and property. For example, in the Yangtze River in China, the introduction of a dam unintentionally prevented carp from spawning downstream, where a commercial fishery was located.
This boosted the carp population and allowed people to continue living off the river, when previously their livelihoods were at stake. Overfishing has caused fish populations to plummet — bad news for the fish, and for the 60 million people in the region reliant on fish in their diets. We provided support to local communities to manage conservation zones and prevent illegal fishing, and as a result local people have found it far easier to live sustainably off the river.
We must commit to recovering freshwater biodiversity, restoring natural river flows and cleaning up polluted water for people and nature to thrive. To learn more about our work with rivers and freshwater, click here. Fundraising Block.
0コメント