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dam, where degradation was expected (Biedenharn 1984). Thepoint of citing these examples is to demonstrate that morphologicalresponse to change in one or more upstream factors is complexand difficult to predict. The specific attributes of system instabilityand stream response depend not only on the magnitude ofchanges imposed on the flow regime and sediment loads, but alsoon the sensitivity and boundary conditions of the downstreamchannel network.3.7.4.3 Basin-wide FactorsIn morphological studies, the flow regime and sediment loadare often cited as the independent variables controlling channelform and process. In reality, these variables are not trulyindependent, but depend in turn on the characteristics of thewatershed including factors such as climate, rainfall-runoffrelationship, natural vegetation, land use, and resourcemanagement. Even if upstream and downstream factors remainconstant, changes in the watershed may trigger instability in thefluvial system that leads to widespread morphological adjustments.For example, urbanization can increase peak flows and reducesediment delivery to the stream network. These changes wouldreinforce one another (see Lane’s balance in Figure 3.10) to drivemarked degradation in the stream draining the urbanized area,with morphological impacts migrating upstream and downstreamthrough the system by slope adjustment and sedimenttransmission, respectively. Afforestation of the headwaters of astream could produce very different morphological adjustmentsdepending whether fluvial processes responding more strongly todecreases in runoff (due to increased consumptive use in thewatershed) or elevated sediment delivery (due to erosion alongforestry roads and ditches). In practice, it is even more difficult topredict the morphological response of a fluvial system to basinchanges than to upstream changes. In attempting to develop thecapability to predict stream response to basin-wide changes,engineers and river managers should make every effort tofamiliarize themselves with the geography of the basin, processesoperating in the fluvial system, sedimentary features, and streammorphology. This knowledge, together with application ofconventional hydrologic, hydraulic, and sediment transportanalyses, represents the currently best option for regionalsediment management and stream stabilization in a changingwatershed.3.8 CHANNELCLASSIFICATIONThe existence of a few distinctive channel forms providesthe rationale for morphological classification of channels. Therelationships linking channel form to fluvial process suggests thatthe morphological classification of a channel may allow the54 Fundamentals of Fluvial Geomorphology and Stream Processes
morphologist to infer process from classified channel form. Thefirst step in classification is to identify whether the channel is eitheralluvial or non-alluvial. An alluvial channel flows in bed and banksthat are composed of material transported by the river underpresent flow conditions. The channel is, therefore, free to adjustdimensions and location in response to changes in flow andsediment load. Conversely, a non-alluvial river is neither selfformednor free to adjust. Examples of non-alluvial rivers includebedrock-controlled channel and streams flowing over very coarseglacial deposits.Many classification schemes rest on channel planformpattern, and stem from Leopold and Wolman’s (1957) classificationof channel planforms as straight, meandering, or braided. In thisrespect, the diagram produced by Brice (1975) is notable becauseit builds on earlier schemes to cover a wide range of commonlyobserved planforms, and has proved useful in engineeringgeomorphic studies (Figure 3.13). Schumm (1981, 1985)recognized an even broader range of channel patterns, althoughthe basic straight, meandering, and braided patterns are stillrecognized within his classification of 14 basic patterns (Figure3.14).Fundamentals of Fluvial Geomorphology and Stream Processes 55
Page 6 and 7: materials. Also, the threshold mobi
Page 8 and 9: ank of a large river. From an engin
Page 10 and 11: eddies in a stream do not scale on
Page 12 and 13: aiding. Braid bars are sediment fea
Page 14 and 15: Sinuosity (P) is a commonly used pa
Page 16 and 17: outcrops, other non-erodible materi
Page 18 and 19: continent (Inglis 1941, 1947, 1949)
Page 20 and 21: instances where the bankfull discha
Page 22 and 23: uses readily available mean daily f
Page 24 and 25: of flows. The results are plotted a
Page 26 and 27: Similarly, in regime theory the con
Page 28 and 29: 3.7 STREAM STABILITY ANDINSTABILITY
Page 30 and 31: It should be noted that the map coo
Page 32 and 33: and slope of the reach are not sign
Page 34 and 35: (a) Bed and Bank InstabilityFigure
Page 36 and 37: the downstream limit of the system
Page 40 and 41: Figure 3.13 - Channel PatternClassi
Page 42 and 43: definition of a graded stream in wh
Page 44 and 45: midwestern experience, while Rosgen
Page 46 and 47: Schumm et al. (1981, 1984) and thei
Page 48 and 49: ut at a much reduced rate. The sedi
Page 50 and 51: • integration of results into eng
Page 52: 68 Fundamentals of Fluvial Geomorph

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