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ut at a much reduced rate. The sediment supply from upstream(Type III) exceeds the sediment transport capacity, resulting inaggradation of the Type IV channel bed. The Type IV reach is alsocharacterized by the development of berms, which aredepositional features along margins of the over-widened channel.These berms represent the beginning of a new inner channel withdimensions adjusted to the flow and sediment regime.Type V reaches represent a state of dynamic equilibriumwith a balance between sediment transport capacity and sedimentsupply. Bank heights in the Type V channel are generally less thanthe critical bank height, and therefore, reach-scale geotechnicalbank instability ceases. However, local bank failures can still existas part of the meander process, or as the results of constrictions,obstructions, or other local factors. The berms, which wereinitiated in the Type IV reach have now become colonized byriparian vegetation forming a compound channel within the larger,incised channel. The equilibrium channel of Type V is of acompound shape, with a smaller inner channel bounded by anarrow floodplain. The original floodplain of the Type I channel isnow a terrace.The CEM addresses the channel stability status within asystem context. Dynamic equilibrium in a Type V reach simplyimplies that system stability has been attained. A Type V reachmay exhibit considerable erosion that is part of the naturalmeander process or some other local process, yet still be classifiedas being in dynamic equilibrium.The primary value of the CEM sequence is to underpinidentification of the evolutionary state of the channel from fieldreconnaissance. The morphometric characteristics of the channelreach types can also be correlated with hydraulic, geotechnical,and sediment transport parameters (Harvey and Watson 1986;Watson et al. 1988). The evolution sequence provides anunderstanding that while reaches of a stream may differ markedlyin appearance, the channel form in one reach is associated withthat in adjacent and remote reaches by an evolutionary process.Form, process, and time relate dissimilar reaches of the streamlinked to complex response and connectivity in the water andsediment transfer systems.3.10 GEOMORPHICASSESSMENTHaving recognized the significance of fluvial geomorphologyto engineering and management of rivers, the problem remains ofgathering the data and qualitative information necessary tocharacterize and define channel form, process, and stability statusin the project river. A thorough geomorphic assessment of theriver and watershed is required. Unfortunately, many engineers64 Fundamentals of Fluvial Geomorphology and Stream Processes
charged with the design of river projects either fail to fullyappreciate the importance of geomorphic assessments, or lack theeducation or training background to perform them adequately.Geomorphic assessment is an essential part of the designprocess for schemes ranging from local bank protection, throughreach-scale habitat enhancement, to master planning for waterresource management in an entire watershed. The aims ofgeomorphic assessment are to provide the baseline informationnecessary to characterize process-form interactions in the river,identify control points and problem reaches, and support division ofthe system into geomorphically distinct sub-reaches that may beindividually classified with respect to morphology. Once thesystem has been characterized and classified, the engineer mayassess the stability status on a reach-by-reach basis and predictthe medium and long-term autonomous evolution under a donothing scenario. This provides a base line against which toassess the morphological responses of the project reach and widersystem to the proposed engineering, rehabilitation, or waterresources project.Perhaps the most important step in any geomorphicassessment is ensuring that the scope and content match theproject goals, authority, stream and watershed characteristics, andavailable resources. There is no standardized or cookbookapproach, but over the last two decades a number of assessmentschemes have been developed and these provide valuableguidance based on direct experience (Schumm et al. 1984;Richardson and Huber 1991; Schall and Lagasse 1991; Shiroleand Holt 1991; Biedenharn et al. 2000b; Robinson and Thompson1993). Typically, existing geomorphic assessment techniques maybe sub-divided into procedural steps dealing with:• assembly of existing and archived data/information in adesk study;• establishment of current channel forms and sedimentfeatures through stream reconnaissance and fieldsurveys;• geomorphic analysis and interpretation of historical andcontemporary information;• stream classification and assessment of stability status atreach scale;• prediction of past and future morphological evolution andresponse to proposed project; andFundamentals of Fluvial Geomorphology and Stream Processes 65
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 38 and 39: dam, where degradation was expected
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 50 and 51: • integration of results into eng
Page 52: 68 Fundamentals of Fluvial Geomorph

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