How does a river system change from upstream (i.e. in the mountains)
to downstream?Why do streams meander?  How in meandering  related to
the velocity of water flow within a meandering stream?

Hi Chuckie1,

I tried to answer your query point by point. Simply press the "Shift"
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"How does a river system change from upstream (i.e. in the mountains)
to downstream?"

When you say upstream, it means the direction that is contrary to the
flow of a river or stream. All flowing body of water flow in one
direction only and as such, none can flow against its natural
direction. As an example, you cannot find a waterfall flowing up or a
stream or river flowing up a mountain. Given these, I take your
question as, "How does water flow down from the mountain to the river
and eventually, to the sea?" Water don't just appear high up in the
mountain so there should be a source. Here's a simple explanation of
how it starts:

Water from the ocean is vaporized by the heat of the sun. This is
called evaporation. The vaporized water condense high up in the sky to
form clouds. When too much water vapors are added to the cloud, it
becomes heavy and saturated. Soon, water falls down as rain. Rain will
fall down the mountain which will fall down as streams which become
bigger and merge into a river, which eventually flows out to the sea.
Then the cycle repeats again.

Here are links to help you better understand this cycle:

U.S. Environmental Protection Agency
THE WATER CYCLE
http://www.epa.gov/OGWDW/kids/cycle.html

The University of Washington
THE WATER CYCLE
http://www-k12.atmos.washington.edu/k12/pilot/water_cycle/grabber2.html

KidZone
THE WATER CYCLE
http://www.kidzone.ws/water/


"Why do streams meander?"

There are many reasons why streams meander or flow in a winding
course. One cause is diversion. No matter how straight water flows
down a mountain, it will eventually encounter a rock, stick, or any
other body that will cause it to become diverted from its original
path. Other reasons are the angle of the surface where it flows, the
speed of flow, etc. The hardness or softness of a surface is also a
factor. Water will erode softer surfaces than hard ones and will
eventually form a natural channel where water water will flow. Streams
tend to meander naturally and vary in width, depth and velocity based
on the surface on which it flows. Older, flatter streams meander more
than younger, steeper streams.

Here are some links that can help you understand this subject:

Conservation Commission of Missouri
UNDERSTANDING STREAMS
http://www.conservation.state.mo.us/fish/streams/under/

Beall High School Science Classes
INVESTIGATION : A MINI-VIEW OF A RIVER
http://www.geocities.com/bhwater2000/StreamInv.html

"How is meandering related to the velocity of water flow within a
meandering stream?"

I believe this has been covered in the links above. As explained
before, water will erode softer surfaces than hard ones and will
eventually form a natural channel where water water will flow. This
means that the faster the rate of flow (velocity ) water, the faster
it erodes a surface. So you can imagine a surface where water flows
exactly between a soft surface and a hard surface -- both will be
eroded, but since the rate of erosion will be faster on the softer
side, water will eventually veer away from the harder surface.

Here are more links to assist you:

National Park Service (NPS) on the Web
CHANGING LANDFORMS IN MIDSTREAM
http://www.nps.gov/brca/Geodetect/Landfroms/stream%20channels.htm


You can still fine additional references from the last three links
below.

Search strategy:

"water cycle"
://www.google.com/search?q=%22water+cycle%22&cat=&hl=en

"streams meander"
http://www.fish.washington.edu/naturemapping/water/1qualnv.html

meandering "water flow" streams
://www.google.com/search?q=meandering+%22water+flow%22+streams&hl=en&lr=&ie=UTF-8&oe=UTF-8


I hope this helps you. Should you have any comments/questions, please
feel free to post your clarification before rating this and I'll
attend to you as soon as possible. Thanks for asking.

Best regards,
Feilong

When felong said water in a body of water can flow in one direction
only, I was challanged. Whirlpools occur and tide direction change
does not occur at the same instant in all parts of a body of water.
Also the wind can cause surface water to move in a different (even
opposite direction) to water at mid depth. This is not important to
the question or the answer which is otherwise excellent.   Neil

Meandering is not thought to be caused by differences in resistance to
erosion. Meanders occur in regions where the stream's velocity is
insufficient to keep its sediment load in motion and it begins
depositing coarser material.

At any point where astream is following a curved path, the water on
the inside of the bend is moving slower than the water on the outside,
so deposition of features called "point bars" is occurring on the
inside of the curve at the same time that the water on the outside of
the curve is eroding the bank. Thus through time, the curve becomes
increasingly sharp, giving rise to the typical "snakey" shape of a
meandering stream.

As point in fact, a meandering stream is almost always cutting back
and forth across its own floodplain, eroding the stream deposits that
it, itself, laid sometime earlier in its history.

For more information see

http://daac.gsfc.nasa.gov/DAAC_DOCS/geomorphology/GEO_4/GEO_CHAPTER_4.HTML
http://www.gcrio.org/geo/channel.html
http://www.geog.ouc.bc.ca/physgeog/contents/11j.html