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ciated with large channel widths while the lower elevations at Sections 47 and 50 are due to their small widths. Changes in channel width which occur concurrently with variations in channel-bed elevation and lateral migration are simulated, Width changes are characterized by the gradual widening at those initially nar- row sections, notably at Sections 47, 49, 50, 51, 57, 58 and 59 and re- ductions in width at initially wide sections, notably at Sections 53 and 54. Initial and simulated final cross-sectional profiles of these sections are shown in Fig. 3 together with some measured profiles, Simulated channel width at the peak flood (shown in Fig. 1) is highly uneven in its spatial variation along the river. This variation is gradually reduced during the flood as reflected by the simulated final cross-sectional pro- files in Fig. 3. By comparing the initial and final channel-bed profiles, one finds that widening at a section is through bank erosion and that the reduction in width is usually through sand-bar formation along the bank(s), Simulated time variation of the cross-sectional profile for Sec- tion 53 shown in Fig. 8 shows the sand-bar formation and the associated reduction in channel width. A picture of this sand bar taken at the end of the flood is shown in Fig. 5. That changes in channel width and channel-bed elevation are closely related may be illustrated by the simulated time variation of the cross- sectional profile at Section 51 (see Fig, 9). Initially Section 51 is on a sand ridge with borrow pits existing on both sides. Gully erosion through this sand ridge during the first flood is simulated, followed by gradual widening and lessening of the gully depth during the second flood. The maximum scour depth is predicted to occur in the initial gully. The sim- ulated results correIate well with measurements at this section shown in Fig. 3, in which the uneven final channel-bed profile as measured is related to the removal of several piers during the flood. Lateral migration of the channel at Sections 44, 45, and 46 in the river bend as simulated is illustrated by the time variation of the cross-sec- tional profile at Section 46 (see Fig. 10). Lateral migration is through gradual erosion of the concave bank and deposition on the convex bank. 50 San Dieguito River Section 53 - looking upstream 40 ;; J!! -----~------------.=---- ____.._.__ti.~~~~...~'1!2ri;;;:;;t~' ~-------~~-- ------ .,,_______~,.. At peak flood Sand ptt (T =66 hrs,) Sand pit Initia! After 1 st flood (T =50 hrs,) 10 1600 laoo 2000 Station, feet 2200 2400 FIG. a.-Simulated Cros..SectIonaI Changes at Section 53 167 16