chapter 3 fundamentals of fluvial geomorphology and stream ...

11 6 112 7 213 8 314 9410 5Figure 3.14 – ChannelClassification Based on Patternand Type of Sediment Load(after Schumm 1981)Knighton (1998) related Schumm’s 14 patterns toinvestigations by Carson (1984a,b), Knighton and Nanson (1993),and Nanson and Knighton (1996). Knighton (1998) noted that thepatterns in Figure 3.14 are related to the classification by the typeof sediment load (Schumm 1976): bed load, mixed load, andsuspended load. Types 1 through 5 are bed load streams, Types6 through 10 are mixed load streams, and Types 11 through 14 aresuspended load streams. Carson (1984a,b) specified two types ofwandering, gravel-bed rivers. The first is characterized by veryrapid bend migration and frequent chute cutoffs of point bars,similar to Type 3. A second wandering-type is similar to Type 14,with vegetated islands separating most of the channels. Knightonand Nanson (1993) point out that coarse-grain, anastomosingchannels do exist. Therefore, despite the variety of channelpatterns that have been investigated and discussed, a continuumof channel patterns does exist and these patterns are controlled bythe interaction of a series of continuous variables. Figure 3.14suggests some of the variables that should be considered, such assediment size and transport mechanism, while Bledsoe’s (1999)logistic threshold approach indicates that specific stream power,relative strength of the bed and bank materials, and sediment sizeare also important (Figure 3.2).In parallel with the development of his morphologicalclassification, Schumm (1977) considered the type of sedimentload being transported by the stream, the percentage of silt andclay in the channel bed and banks, and the stability of the channelto describe the morphology associated with stable conditions andthe morphological changes expected in response to instabilitythrough aggradation or degradation (Table 3.4). For purposes ofthis classification system, a stable channel complies with Mackin'sFundamentals of Fluvial Geomorphology and Stream Processes 57