How do creeks start

The name delta comes from the capital Greek letter delta, which is a triangle, even though not all deltas have this shape. A triangular shaped delta forms as the main stream channel splits into many smaller distributaries.

As the channel shifts back and forth dropping off sediments and moving to a new channel location a wide triangular deposit forms. There are three types of beds that make up a delta Figure The first particles to be dropped off are the coarsest sediments and these form sloped layers called foreset beds that make up the front edge of the delta.

Further out into calmer water, lighter, more fine grained sediments form thin, horizontal layers. These are called bottomset beds. During floodstage, the whole delta can be covered by finer sediments which will overlie the existing delta. These are called topset beds. These form last and lie on top of the rest of the delta.

Not all large rivers form deltas as they meet the ocean. Whether a delta forms depends on the action of waves and tides. If the water is quiet water such as a gulf or shallow sea, a delta may form. If the sediments are carried away, then no delta will form.

Sediments brought to the shore and distributed along coastlines by longshore transport form our beaches and barrier islands. If a river or stream suddenly reaches nearly flat ground, like a broad flat valley or plain, an alluvial fan develops at the base of the slope Figure An alluvial fan is a curved top, fan shaped deposit of coarse sediments that drop off as the stream suddenly loses velocity.

The fan spreads out in a curve in the direction of the flat land as many stream channels move across the curved surface of the alluvial fan, forming and unforming many channels as sediments are deposited. Alluvial fans generally form in more arid regions. The stream forming the alluvial fan runs from the mountains in the southwest lower left corner of the photograph toward the flatter land to the northeast upper right.

The green rectangles are farm fields which utilize the distributed water. Skip to main content. Surface Water. Search for:. Streams and Rivers Fresh water in streams, ponds, and lakes is an extremely important part of the water cycle if only because of its importance to living creatures. People have used rivers since the beginning of civilization as a source of water, food, transportation, defense, power, recreation, and waste disposal.

A stream originates at its source. The source is likely to be in the high mountains where snows collect in winter and melt in summer, or a source might be a spring.

The source is known as the headwaters or the head of the stream. The smaller of the two streams is a tributary of the larger stream. A stream may create a pool where water slows and becomes deeper. The point at which a stream comes into a large body of water, like an ocean or a lake is called the mouth. Review Questions What are the three kinds of load that make up the particles a stream carries. Name and define each type. What effect does it have on the work of a stream? Eventually, most rivers empty out into the sea.

Many rivers begin as a small trickle of water running down a mountain as a result of melting ice and snow on the mountain tops. Lakes form when water flows into a hollow in the ground at a faster rate than it can escape. For example, melting ice and snow feed lakes in the valleys below. As the river flows downhill, it carries away eroded debris particles of rock to the lowlands, and eventually to the sea.

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Text on this page is printable and can be used according to our Terms of Service. Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Floods are events where water overflows onto land that is typically dry. This can occur when there is a large amount of rain, rapid snow or ice melt, a blast of water onto a coastline during a storm, or the failure of manmade infrastructures, such as dams or levees.

Floods are among the most expensive and frequent natural disasters in the United States, and as the impacts of climate change are more acutely felt, floods are expected to worsen. In addition to property damage, floods, on average, kill more people than tornadoes, hurricanes, or lightning strikes in the United States each year.

Learn more about floods with these resources. A river is a large, natural stream of flowing water. Rivers are found on every continent and on nearly every kind of land. The surrounding river basin has a population of more than four hundred million people. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content.

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