chapter 3 fundamentals of fluvial geomorphology and stream ...

• 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