Geomorphic Classification of Rivers

Geomorphic Classification of Rivers 735 Channel type Suspended load Mixed load Bed load Low Low 1 shift High Straight 2 Alternate bar 3 a Neck cutoff Meander shift Gradient 3 b Meandering Channel pattern Width-depth ratio 4 Relative stability Chute cutoff Legend Meander shift Channel boundary Flow 5 Bars Low High High Braided Avulsion Thalweg shift High Relative stability Low (3 %>) Low Bed load/total load ratio High (>11%) Small Sediment size Large Small Sediment load Large Low Flow velocity High Low Stream power High Figure 4 Schumm’s (1963a, 1977, 1981, 1985) classification of alluvial rivers. Reproduced from Figure 4 in Schumm, S.A., 1981. Evolution and response of the fluvial system, sedimentological implications. In: Ethridge, F.G., Flores, R.M. (Eds.), Recent and Nonmarine Depositional Environments. SEPM (Society for Sedimentary Geology), Special Publication 31, Tulsa, OK, pp. 19–29, with permission from SEPM; Figure 1 in Schumm, S.A., Meyer, D.F., 1979. Morphology of alluvial rivers of the Great Plains. In: Riparian and Wetland Habitats of the Great Plains. Proceedings of the 31st Annual Meeting, Forestry Committee. Great Plains Agricultural Council Publication 91, Lincoln, NE, pp. 9–14; and Figure 3 in Shen, H.W., Schumm, S.A., Doehring, D.O., 1979. Stability of stream channel patterns. Transportation Research Record 736, National Academy of Sciences, Washington, DC, pp. 22–28, with permission from Transportation Research Board. 1996b),andBrierley and Fryirs (2005). The above approaches rivers similarly recognizes that characteristic floodplain derived from Schumm (1963a, 1977, 1981, 1985) provide morphologies reflect specific styles of fluvial processes (Fig- powerful conceptual models for understanding basin controls ure 7) and highlights genetic (i.e., evolutionary) sequences of on channel morphology, as well as likely response to perturb- channel and floodplain morphology in response to environ- ations in discharge and sediment supply, but are mainly mental perturbations (changes in stream flow and sediment qualitative and, in most cases, have been developed for supply). A similar genetic coupling of river and floodplain large floodplain rivers. Furthermore, these approaches are processes is also used in the river styles classification typically descriptive (associating physical conditions with chan- (Brierley and Fryirs, 2005), which further recognizes that nel morphology, but not explaining the underlying processes) channel–floodplain interactions may be modulated by ex- or involve a mixture of descriptive and process-based trinsic factors (e.g., bedrock outcrops, glacial moraines, relict interpretations. terraces) in partly confined rivers (a transitional morphology between confined and unconfined river valleys (Brierley and Fryirs, 2005; Jain et al., 2008; Fryirs and Brierley, 2010), 9.36.3.4 Channel–Floodplain Interactions sometimes referred to as semialluvial (e.g., Brice, 1982)). Interactions between the river and its surrounding floodplain Channel–floodplain interactions are also implicit in classifi- can exert strong controls on physical processes, morphology, cations of channel pattern (Section 9.36.3.3), but may not be response potential, and the quality and diversity of habitat for articulated. both the river and its floodplain. Several classifications ex- Because channel–floodplain approaches focus on overbank plicitly incorporate channel–floodplain interaction. In one of flows that are capable of eroding banks and doing work on the the earliest approaches, Melton (1936) synthesized work from floodplain, they tend to describe longer term processes and prior studies (Gilbert, 1877; Powell, 1896; Fenneman, 1906; recognize that channel and floodplain conditions represent a Davis, 1913; Matthes, 1934) to classify channels based on distribution of flood events, with smaller floods modifying whether their floodplains were formed by meandering (lateral and sculpting the morphologic legacy of larger floods (Melton, accretion), overbank (vertical accretion), or braiding pro- 1936; Stevens et al., 1975). Furthermore, different scales of cesses. Nanson and Croke’s (1992) classification of floodplain bedform and floodplain features may occur, representing a.

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