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Chapter 4: Fluvial Processes in Riparian Areas
Channel Morphology
- Channel morphology is the study of the form and physical characteristics of a channel.
- Channels and their floodplains are two dominant morphological features of riparian areas.
- Channel form refers to the shape of the channel.
Its major characteristics are:
- Patterns:
- straight: channels have a single thread that is straight;
- meandering: channels also have a single threads but the channels has many curves;
- braided: channels have multiple threads with many sand bars that migrate frequently;
- anastomosed:
streams that also multiple
threads but do not migrate laterally.
Figure 4.4. The channel stream patterns: a) straight, b) braided, c) meandering and d) anastomosed.
- Sinuosity is calculated as the distance water flows along the deepest channel path divided by the straight line distance between starting and ending points.
- Meander length is the distance for the
beginning to the end of meander.
Figure 4.5. Meander length, radius of curvature, and measurements needed for computing sinuosity.
- Cross section is described by the two-dimensional shape of the channel perpendicular to the direction of flow. The shape of the cross section will depend on where we are along the stream.
- Width to depth ratio is the width of the
channel divided by the average depth
of the channel.
Figure 4.6. General channel cross section; x indicates channel width and y indicates channel depth).
- Channel gradient is the slope of the stream and can be computed as the length of the channel divided by the difference in elevation of the upper and lower end points.
- Thalweg is the deepest part of the channel along which the water flows.
- Scarp is typically the outside bend of
the channel that erodes.
Figure 4.7. A cross section along a stream bend; also the thalweg and the scarp are shown.
- Patterns:
- Floodplains
Figure 4.8. Part of the floodplain of Fossil Creek watershed.
- Flood plains act as overflow buffers and serve a critical function in reducing the downstream impacts of floods.
- Floodplains comprise the area adjacent to channels over which out of bank flows are diffused.
- Floodplains form over time as a result of flood inundations. Water moving over a floodplain travels at a lower velocity than the channel flow, and sediment is deposited.
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