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<br />II. DI'.l'llIIl>>.X~<J!I <br /> <br />Alluvial rivers are self-regulatory in that they adjust their charac- <br />teristics in response to any change in the envirol1llent. These envirormental <br />changes may occur naturally, as in the case .of climatic variation or changes <br />in vegetative cover, or may be a result of such human activities as danming, <br />river training, diversion, sand and gravel mining, channelization, bank <br />protection, and bridge and highway construction. Such changes distort the <br />natural quasi-equilibrium of a river; in the process of restoring the <br />ecpilibrium, the river will adjust to the new conditions by changing its <br />slope, roughness, bed-illaterial size, cross-sectional shape, or meandering <br />pattern. Within the existing constraints, anyone or a canbination of these <br />characteristics may adjust as the dver seeks to maintain the balance <br />between its ability to transport and the load provided. <br /> <br />River channel behavior often needs to be studied for its natural state <br />and responses to the aforanentioned human activities. Studies of river <br />hydraulics, sediment transport and river channel changes may be through <br />physical modeling or mathematical modeling, or both. Physical modeling has <br />been relied upon traditionally to obtain the essential design information. <br />It neverthelesS often involves large expenditure and is time consuming in <br />model construction and experimentation. What limits the accuracy of physi- <br />cal modeling is the scale distortion which is almost unavoidable whenever it <br />involves sedimentation. <br /> <br />Mathematical modeling of erodible channels has been advanced with the <br />progress in the physics of fluvial processes and canplter techniques. A <br />evaluation of existing models was made by the National Academy of Sciences <br />(1983) . RecomlIendations in this report has been beneficial for subsequent <br />model developnent. since the actual size of a river is anployed in mathema- <br />tical modeling, there is no scale distortion. The applicability and accura- <br />cy of a model depend on the physical foundation and numerical techniques <br />anployed . <br /> <br />and <br /> <br />The traditional regime analyses of rivers are <br />their long-term adjustments in equilibrium. <br />3 <br /> <br />limited to regime rivers <br />The hydraulic geanetry, <br />