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River Morphology . e FIGURE 2. 1 River Classnication (Reprinted from Brice, 1983) Nonsinuous Braided '9 - ----~---- - .. "'- ... .. -----. --- -- ~ .. !!' CD ~ 1Il '6 l5 .. 8- 0; ~ ~ '. f! ~ Sinuous Braided ~ Sinuous Point Bar Sinuous Canalnorm Anabranching is a condition which occurs on many Colorado Rivers and has diverse origins. II may be caused by: (1) blockage of a main channel by ice jams, (2) geological constraints such as bed rocks, or (3) topographical effects. Field and laboratory findings by Leopold el al. (1964) have shown thai anabranches are usually steeper than the undivided channel under a quasi-equilibrium condition. This may be explained from the viewpoinlthal the anabranches have a lower lransport capacily per unil water dischaJge and hence need steeper slopes 10 maintain the unifonn sedimenlmte through divided and undivided reaches. Anabranching therefore represents an adjustmenl in channel pattern in its adaptation to changes in terrain (Chang 1988). 2.2,3 Channel Cross Sections. Figure 2-2 shows a plan view of a river between the apexes of Iwo beds. Also shown on the figure are typical sections at the bend, lransition. and crossing of the reach. Section A-A is a typical section of a river bend. While generally triangular, the shape of a bend cross section varies significantly nol only from stream to stream, bul from reach 10 reach within a given river. . According to Chang (1988), the tlow in a bend is under the intluence of centtifugal accelemtion, which induces (I) spiral motion in tlow and (2) superelevation in water surface. This spiral motion (shown in Figure 2-3) is also referred to as helical motion. secondary currents, or lranSverse circulation. In alluvial channel bends. these secondary currents move particles away from the concave bank and toward the convex bank; Colorado Erosion Control Manual 5