Fundamentals of Fluvial Geomorphology and Channel Processes
Table 3.2 presents a summary of this classification system and describes the response of the river
segment to instability and a description of the stable segment. It is very important to note that the work on
which this classification was based was conducted in the midwestern U.S.; therefore, the classification
system represents an interpretation of empirical data. Extrapolation of the classification beyond the
database should be done cautiously.
Schumm and Meyer (1979) presented the channel classification shown in Figure 3.12, which is
based on channel planform, sediment load, energy, and relative stability. As with any classification system,
Figure 3.12 implies that river segments can be conveniently subdivided into clearly discernable groups. In
reality, a continuum of channel types exists and the application of the classification system requires
judgement.
Other stream classifications include those by Neill and Galay (1967) and by Rundquist (1975).
These systems go well beyond a description of the channel, and include description of land use and
vegetation in the basin, geology of the watershed, hydrology, channel bed and bank material, sediment
concentration, channel pattern, and channel stability.
Rosgen (1994) presented a stream classification system similar to the Runquist (1975) system. A
primary difference between the two systems is that planform and bed material character are combined into
one code, improving the ease of use. Rosgen (1994) also included an entrenchment ratio, which is the
ratio of the width of the flood-prone area to the surface width of the bankfull channel. Like Runquist
(1975), Rosgen (1996) has also added valley type classification. Table 3.3 is a summary of delineative
criteria for broad-level classification from Rosgen (1994). Each of the stream types can be associated with
dominant bed material types as follows: Bedrock - 1, Boulder - 2, Cobble - 3, Gravel - 4, Sand - 5, and
Silt/Clay - 6.
With some modifications to Figure 3.12, Figure 3.13 is a combination of some concepts of
Schumm and Rosgen. Schumm's classification system was heavily dependent on his Midwestern
experience, while Rosgen's experience began in steep mountain streams. In addition, Schumm's (1977)
classification did not specifically include incised channels, which are included in Rosgen's (1994) F and G
classes. Figure 3.13 includes C, D, DA, and E classes, and could be expanded to include all of Rosgen
(1994) classes. The value of Figure 3.13 is to demonstrate that moving from class to class is a predictable
response that manages energy, materials, and channel planform to reestablish a balance of sediment and
water discharge with sediment and water supply.
3.2
CHANNEL EVOLUTION
The conceptual incised channel evolution model (CEM) has been of value in developing an
understanding of watershed and channel dynamics, and in characterizing stable reaches of these channels.
The sequence was originally used to describe the erosion evolution of Oaklimiter Creek, a tributary of
Tippah River in northern Mississippi. Simon and Hupp (1987) have developed a similar model of channel
evolution.
38
Previous Page
