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justment in resistance to seek equal power expenditure along its course. A degrading reach usually has a higher channel-bed elevation and en- ergy gradient than its adjacent reaches. Formation of a narrower and deeper channel at the degrading reach decreases its energy gradient due to reduced boundary resistance and lower bed elevation. On the other hand, an aggrading reach is usually lower in channel-bed elevation and energy gradient. Widening at the aggrading reach increases its energy gradient due to increased boundary resistance and higher bed elevation. These adjustments in channel width reduce the spatial variation in en- ergy gradient and total power expenditure of the channel. Since sedi- ment rate is directly proportional to ..,QS (1), these adjustments also fa- vor the establishment of channel's equilibrium in sediment load, that is, equal sediment rate along the reach. a.anges in Channel-Bed Profile.-After the banks are adjusted, the remaining correction for .1A, obtained in sediment routing is applied to the bed. Erosion and deposition at a cross section have different pat- terns. Generally speaking, deposition tends to be more uniformly dis- tributed in that it tends to build up the channel bed in horizontaIlayers. This process of deposition is often accompanied by channel widening. On the other hand, channel-bed erosion tends to be more confined with greater erosion in the thalweg. This process is usually associated with a reduction in width. These channel adjustments reduce the spatial vari- ation in power expenditure as the river seeks to establish a new equi- librium. In the model, deposition at an aggrading section starts at the lowest point, and it builds up the channel bed in horizontal layers. For a degrading section, the change in area is distributed in proportion to the effective tractive force, T - Ta, along the bed, where T is the local tractive force and Ta is the critical tractive force. Lateral Migration.-In a river bend, erosion on the concave bank and deposition on the convex bank results in lateral migration of the chan- nel. This river channel change is attributed to the transverse currents in the river bend. In the present model, the mechanism for lateral migra- tion is provided by transverse currents, transverse sediment movement and the continuity equation for sediment in the transverse direction. Bottom filaments of stream current in a bend have a component in the transverse direction toward the convex bank. The role of transverse ve- locity consists in moving the bottom layers of the stream away from the concave bank. Erosion of the concave bank occurs under the action of the transverse velocity which, being directed down the slope and added to the gravitational force, scours particles of the material on the concave bank. As particles are scoured from the concave bank, they tend to be deposited on the convex bank, resulting in a shift in channel course. Rozovskii (14) studied the angle of deviation of bottom filaments from the direction tangent to the centerline of a bend. Kikkawa, et al. (10, p. 1332) developed an analytical relationship for the angle of deviation ~ of mean particle path from the tangential direction. In the relationship, II is expressed as a function of the flow direction of bottom filaments, transverse bed slope, and flow and sediment characteristics. With this relationship, the transverse sediment rate is related to the longitudinal sediment rate as 160 9