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<br />52 <br /> <br />. <br /> <br />3.9 Lateral Migration <br />3.9.1 General <br />Alluvial channels of all types deviate from straight alignment. The <br />thalweg oscillates transversely and initiates the formation of bends. Lat- <br /> <br />eral migration tendencies can be quantitatively evaluated based on a know- <br /> <br />ledge of geomorphic concepts. A meandering alluvial river has three addi- <br />tional degrees of freedom to adjust its geometry beyond those for a straight <br /> <br />alluvial river (i.e., meander wavelength, wave amplitude, and radius of <br /> <br />curvature may all change with time). The extend of possible lateral channel <br /> <br />migration depends upon: (1) the meander belt width; (2) the rate and direc- <br />tion of the channel's lateral migration; and (3) the possible change of <br />channel alignment due to the development of cutoffs upstream and downstream <br />of the site. <br />The probable maximum meander wavelength, the probable maximum wave <br /> <br />amplitude, and the probable maximum radius of curvature during the project's <br /> <br />lifetime are estimated by the relations between meander dimension parameters. <br /> <br />Aerial photographs of the past and present are extremely useful in assessment <br /> <br />of the changes of all meander dimension parameters. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />3.9.2 Lateral Migration Potential <br />The potential for lateral migration increases as a river becomes more <br /> <br />sinuous. If the river system under consideration is straight or has a low <br /> <br />sinuosity potential, lateral migration will be small. figure 3-4 shows the <br /> <br />individual meander characteristics, ^ the meander wavelength, a the ampli- <br /> <br />tude, R the radius of curvature, and B top width of the channel. <br /> <br />In order to understand the migration process of a specific river system <br /> <br /> <br />thoroughly, a large reach of river should be studied to determine the range <br /> <br /> <br />of meander characteristics. The lateral migration potential at a specific <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br />