Fundamentals of Fluvial Geomorphology and Channel Processes
less than ten years, and numerous minor projects are designed and built within the limitations
of present time. Project life often extends into graded time. From a geologists temporal point
of view, engineers built major projects in an instant of time, and expect the projects to last for
a significant period.
In river related projects time is the enemy, time is our friend, and time is our teacher.
We must learn all we can by adopting a historical perspective for each project that we
The physical size of the stream may impose limits on the type of planned
enhancements to the stream. For example, many variations of anchoring trees along the bank
have been successfully used along small and moderate size streams to provide cover and to
decrease erosion of the bank. Anchoring of trees along the bank is a reasonable method of
stabilization. However, for large rivers that may have bank heights of 30 feet and a yearly
water surface elevation fluctuation of 20 to 30 feet, the anchored tree may be an unreasonable
method for stabilization. Applications designed for a small stream may not be directly
transferrable to larger streams. If we are to transfer techniques for enhancement from stream
to stream; we must also understand the design principles of those techniques. Principles, such
as increasing the cover and decreasing the water velocity at the water-bank interface are
transferable; however, the direct technique may not be transferable.
Now it is time to give you a brief introduction into what you may see when you go
to the field. The following discussion will be confined primarily to depositional landforms
along meandering rivers, and a little information concerning terraces.
A floodplain is the alluvial surface adjacent to a channel that is frequently inundated
(Figure 2.2). This is a simple definition of a floodplain; however, the concept that the
bankfull discharge is the sole discriminator between channel-forming and floodplain-building
process is especially difficult. Although much of the literature until the 1970s suggested that
the mean annual flood was the bankfull discharge, Williams (1978) clearly showed that out
of thirty-five floodplains he studied in the U.S., the bankfull discharge