110117 - braided rivers

In the classification of rivers, there are four different fluvial styles:  meandering (one very curvy channel), straight (one straight channel), anastomosing (multiple laterally stable channels), and braided (multiple laterally unstable channels).  A river may flow through all four fluvial styles along its length.  The primary variables controlling fluvial styles are the slope and sediment load of the river. 

Braided rivers are most often found where there are young, rapidly eroding mountains (Canada, Alaska, South Island of New Zealand, Himalayas).  Individual channels in a braided river can behave like a meandering, straight, or anastomosing river.  See examples of braided rivers below:

Rakaia River – South Island, New Zealand

(from Google Earth)
  

 Brahmaputra River, Tibet

(from NASA Visible Earth)
  

 Dibang River, Arunachal Pradesh, India

(from Google Earth)
  

 Athabasca River – Alberta, Canada

(from Google Earth) 

The studio will use the operative and organizational characteristics of braided rivers as a basis for a map dealing with multiples and change over time.  To begin your braided river map (described in the first handout), first select a section of river.  Use NASA's Visible Earth website, Google Earth, or another source to find an appropriate image.  The image must be a satellite view from directly above.  Like the examples here, the image you select must be at a location where the river becomes relatively wide and contains many individual channels. 

110117 - braids

A braided river is not truly braided.  Or at least it is impossible to identify any real braiding of strands in an image of the river because individual flows of water appear to intersect each other.  Mathematically speaking, a braid is a type of knot.  A knot is a continuous curve in space that does not intersect itself.  So in a braid, individual strands pass over or under each other without intersecting.

example of a braid

Described by Adams in The Knot Book, "A braid is a set of n strings, all of which are attached to a horizontal bar at the top and bottom.  Each string always heads downward as we move along any one of the strings from the top bar to the bottom bar.  Another way to say the same thing is that each string intersects any horizontal plane between the two bars exactly once."

Given a specific number of strands, there is a specific

number of ways the strands can cross each other...

...and individual crossings can be combined 

to form a more complex braid.

Braids can be 'multiplied' by stacking 

them on top of one another.

Read the excerpt from The Knot Book (posted here on the blog) not necessarily to understand all the mathematics of knotting and braiding, but to help imagine different types of braids and how to manipulate them.