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• integration of results into engineering design to optimizeperformance.For more detailed reviews of practical and procedural issuesin geomorphic studies and assessment, the reader is referred toarticles by the third author (Thorne 1998, 2001).The results of geomorphic assessments are rarely clear cut.More often, the individual elements of the assessment produceoutcomes that are equivocal or even contradictory. For example,the specific gage record for a hydrological station may indicate thatstages for a given discharge have decreased significantly, whilethe few available repeat cross sections from the same period showvariations in bed topography but no evidence for discerniblechange, and stream reconnaissance indicates that the stream ishydraulically connected to the floodplain. The specific gagerecords suggest that the stream has degraded, but there is a lackof supporting evidence from resurveyed cross sections and streamreconnaissance that the streambed and floodplain levels aremutually-adjusted. In these situations, a level of confidence mustbe assigned to morphological conclusions based on differentcomponents of the assessment, based on the quantity, quality, andreliability of the data and the assessor’s experience in applying thetechniques involved. It may then be possible to reconcileapparently contradictory results by weighing the levels ofconfidence associated with each one. It is emphasized soundjudgment, based on insight and experience, that is essential foraccurate geomorphic assessment.Obviously, geomorphic assessment alone can neverprovide a proper basis for engineering analysis or design. It is,however, of value when combined with computational andanalytical methods for stable stream design. The widercontribution provided by geomorphic assessment is to establishthe system context and framework within which the designer may:• select hydrodynamic and sediment transport equationsappropriate to the stream and conditions;• match design of stable stream dimensions that mimicnatural channel forms and diversity while meeting projectgoals;• use computer models matched to the alluvial setting andincorporating existing geologic and artificial controls topredict morphological response of the stream system toproposed rehabilitation measures;• integrate environmental features effectively intomorphological and engineering aspects of the project;66 Fundamentals of Fluvial Geomorphology and Stream Processes
• anticipate maintenance requirements and optimize thedesign to ensure that the benefits are sustainable; and• consider and propose the scope of a Post-ProjectAppraisal (PPA) and monitoring regime necessary toestablish the strengths and weaknesses of projectperformance.Geomorphic assessment alone is not sufficient to guaranteethat a project will perform adequately with regard to morphologicaland environmental goals, but it is a valuable and necessarycomponent of the integrated stream design process that isessential to ensure long-term sustainability in river engineering andmanagement projects.3.11 SUMMARYFluvial geomorphology, analytical river mechanics, andsound engineering judgment together provide the foundations forsound river engineering, rehabilitation, and management. Insightsand understanding provided by geomorphic principles andidentification of causal links between channel form, fluvialprocesses, and connectivity of the river system can be invaluablein the design of river projects and management strategies. This isthe case, not only because the engineering-geomorphic approachis consistent with environmental goals such as minimizing negativeimpacts and maximizing biodiversity, but also because solutionsthat recognize and deal with the causes rather than the symptomsof stream problems represent better engineering. Manyengineering stabilization and rehabilitation projects have failed, notas the result of deficient hydraulic or structural design, but ratherbecause the significance of geomorphology to the project and theproject to geomorphology have not been identified and accountedfor in the design. Experience is accumulating that engineeringdesigns guided by knowledge of the fluvial system are able toavoid having to attempt to ‘tame the river,’ instead working with theriver to produce schemes that have lower long-term maintenancerequirements. Engineering-geomorphology thereby opens thedoor to cost-effective, sustainable solutions that do not commitfuture generations to heavy and expensive maintenance.Fundamentals of Fluvial Geomorphology and Stream Processes 67
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 48 and 49: ut at a much reduced rate. The sedi
Page 52: 68 Fundamentals of Fluvial Geomorph

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