fluvial - MEANDERING STREAMS AND FLOODPLAINS

Expand the MEANDERING STREAMS AND FLOODPLAINS folder.

In contrast to braided streams, meandering streams are formed in landscapes with little relief, are generally slower moving, and carry finer sediments. In addition, water flow within meandering stream typically is constrained to a single channel.

As their name suggests, meandering streams are identifiable by their sinuosity, or the bends and turns of the stream channel across a floodplain. The meander of the channel occurs with the scouring of the channel on the outside of the bend (where flow is faster) and deposition on the inside of the bend (where flow is slower).

This constant erosion or removal of sediment from cutbanks and deposition of sediment from point bars produces the movement of the meander across the landscape, with past meanders evident from oxbow lakes and meander scars.

Click Stream Process Animation and view the animation.

Erosion and deposition occurs primarily during periods of flooding. Many rivers are prone to flooding, with some large flooding events changing the course of the stream channel (by bypassing the meander altogether and producing a straight reach). While natural or artificial levees might prevent a stream from flooding, large flood events compromise levees, with water and its suspended sediment spilling over the levees and depositing onto the surrounding floodplain.

Close the Stream Process Animation window. Double-click and select the Mississippi River - Identify Features folder.

Using the following list of meandering stream features, answer Questions 25 to 29 that apply to the Mississippi River map image in Google Earth.

A. Cutbank	B. Inside of meander	C. Meander scar	D. Point bar
E. Deep channel (thalweg)	F. Island	G. Outside of meander	H. Shallow channel
I. Floodplain	J. Low ground	K. Oxbow lake

Question 25: A
Question 26: B
Question 27: C
Question 28: D
Question 29: E

Question 30: Identify two dominant land uses surrounding the river.

Question 31: Do these land uses indicate this area as a floodplain? Explain.

Double-click and select the Mississippi River - Measure Distance folder.
Do the following steps to examine river sinuosity.
1 Verify that Mississippi River - Measure Distance is the only item checked in the Places pane.

2 Go to the Google Earth icon bar and click the Show Ruler tool .

Note: Verify that the simulation control panel is closed:

3 In the Ruler window, click the Line tab and select Miles for the units.
4 Draw a straight line between the two points; that is, click point

and then click point

to
determine the distance.

5 Press the Esc key to stop.

Question 32: What is the length, in miles, of the channel?

Measure the distance of the channel (the meander):

1 In the Ruler window, click the Path tab and set the units to Miles.

2 Click point

and click you as trace the path of the river until you get to point

. Figure 7
shows an example of how your path might appear.

Question 33: What is the length, in miles, of the channel?

The sinuosity index (SI), also known as the meander ratio, calculates how much the stream channel deviates from the shortest path. Straight rivers have a SI close to 1, but this number increases the more a river meanders.

Question 34: Use the following formula to calculate the SI for this reach of the Mississippi River:

SI = channel length / downvalley length =

Close the ruler tool. Uncheck Mississippi River - Measure Distance. Double-click and select the San Juan River - Compare Features folder.

The San Juan River is another meandering stream, yet we do not see the classic oxbow lakes and meandering scars we saw with the Mississippi River.

Question 35: Compute the SI of the San Juan River from point A to point B (show your work).

Question 36: Which river (Mississippi River or San Juan River) has a higher SI?

Use the following navigation steps to examine the terrain:

Press and hold the Shift key.
Use the scroll button on the mouse to see the landscape in 3D. You can also use the Ctrl or Shift keys in combination with the arrow keys to pivot and rotate the image.

Question 37: Explain why there are no classic oxbow lakes or meandering scars.

Condense and uncheck MEANDERING STREAMS AND FLOODPLAINS

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