The Process
In all of the above described channel design methods, channel dimensions are either assumed or
iteratively varied to meet design criteria such as allowable velocities, tractive force, or regime relations.
Analytical design methods. As noted above, the empirical design methods may be appropriate
for reconnaissance level studies, or small rehabilitation projects. However, if the projects are large scale,
or involve significant bed material transport then these methods are not generally suitable, and it may be
necessary to adopt one of the more rigorous analytical design procedures discussed in Chapter 5, Section
5.3.5. While these procedures address more fully the dominant processes in the channel system, it must
be recognized that the data requirements are also much more intensive.
2.4.4
DETERMINE A STABLE CHANNEL MEANDER WAVELENGTH FOR THE
PLANFORM
In some instances, the project goals may require modification of the existing planform. When this
occurs, the meander planform properties must be designed to be compatible with the stable channel
dimensions calculated in the previous step (Section 2.4.3).
The most reliable hydraulic geometry relationship for meander wavelength is wavelength vs. width.
As with the determination of channel width, preference is given to wavelength predictors from stable
reaches of the existing stream either in the project reach or in reference reaches. Lacking data from the
existing stream, general guidance is available from several literature sources (e.g. Leopold et al., 1964).
The meander length is computed from the following equation:
wavelength x valley slope
meander length '
slope
2.4.5
PLANFORM LAYOUT USING THE MEANDER WAVELENGTH AS A GUIDE
One way to accomplish this task is to cut a string to the appropriate length and lay it out on a map.
Another, more analytical approach, is to assume a sine-generated curve for the planform shape as
suggested by Langbein and Leopold (1966) and calculate x-y coordinates for the planform. The sine-
generated curve produces a very uniform meander pattern. A combination of the string layout method and
the analytical approach would produce a more natural looking planform.
Check the design radius of curvature to width ratio, making sure it is within the normal range of 1.5
to 4.5. If the meander length is too great, or if the required meander belt width is unavailable, grade control
may be required to reduce the channel slope. In streams that are essentially straight (sinuosity less than 1.2)
riffle and pool spacing may be set as a function of channel width. The empirical guide of 6-10 channel
widths applies here, with the lower end for steeper channels and the higher end for flatter channels. Two
times this riffle spacing gives the total channel length through one meander pattern.
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