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<br />APPEllDIX E <br /> <br />MODEUNG OF RIVER CHANNEL CHANGES <br /> <br />By Howard H. Chang,' M. ASCE <br /> <br />Aunw:r: A computer-b~ed flood- and sediment-routing model which sim- <br />ulates river channel changes is described together with its application in the <br />case study of a disturbed river. Simulated results of this study are supported <br />by field observations and measurements. This model incorporates the interre- <br />lated changes in channel bed profile, width, and lateral migration in channel <br />bends. These changes reflect, in part. a river's adjustments in power expend~ <br />iture. The interreJation of changes in channel bed. profile and width is illus- <br />trated by a physical example and expJained by the river's tendency to establish <br />equal power expenditure along the channel. Such power transfonnation as- <br />sociated with river channel evolution tends to restore the dynamic equilibrium <br />in sediment transport, that is, equal sediment load along the channel. The case <br />study demonstrates that in the case of severely disturbed rivers, flood-level <br />computation using a fixed-bed model may be quite inaccurate and improved <br />accuracy can be provided by an erodible-bed model. <br /> <br />INTAODUC11ON <br />River channel changes generally include channel-bed aggradation and <br />degradation, width variation, and lateral migration in channel bends. <br />These changes may occur naturally or as a result of a change in the <br />environment. Man is also regarded as a geomorphic agent with certain <br />activities such as sand and gravel mining, bridge construction, river con- <br />trol schemes, etc., having contributed to river channel changes. lang- <br />bein and Leopold (12) maintained that the equilibrium channel repre- <br />sents a state of balance with a minimum rate of energy expenditure or <br />an equal rate of energy expenditure .Iong the channel. Changes induced <br />by nature or men's activities distort the channel equilibrium and there- <br />fore result in river channel changes. <br />The three types of river channel changes in channel-bed elevation, <br />channel width, and lateral migration are closely interrelated to each other <br />and may occur concurrently. Changes in channel-bed elevation are often <br />inseparable from width variation because a channel tends to become ni\I- <br />rower during degradation, and it tends to widen during aggradation. <br />Earlier versions of the FLUVIAL model have considered channel-bed ag- <br />gradation and degradation (3,4,5) and width variation (4,5). The current <br />version FLUVIAL-ll which simulates all three types of changes has been <br />formulated, developed and applied in a case study. This paper describes <br />this model and its application in the case study. Special attention is given <br />to the nature of energy (or power) transformation in alluvial rivers as- <br />sociated with river channel evolution. <br /> <br />ANAL mCAL BACKGROUNO <br />This mathematical model has five major components: (1) Water rout- <br />ing; (2) sediment routing; (3) changes in channel width; (4) changes in <br />channel-bed profile; and (5) lateral migration of the channel. This model <br />'Prof. of Civ, Engrg., San Diego State Univ" San Diego, Calif. <br />Note,-Discussion open until July 1, 1984. To extend the closing dale one month, <br />a written request must be filed with the ASCE Manager of Technical and Profes- <br />sional Publications. The manuscript for this paper was submitted for review and <br />possible publication on November 2, 1982. This paper is part of the 'ournal of <br />Hydraulic Engineering, VoL 110, No, 2, February, 1984, iOASCE, ISSN 0733-9429/ <br />84/0002.0157/$01.00. Paper No, 18578. <br /> <br />157 <br /> <br />6 <br />