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when Lake Hodges spilled. Hydrographs of these floods are shown in Fig. 2. Prior to these events, Lake Hodges had not spilled for 26 yr. River Channel Changes.-Significant changes in the river channel were observed after the March, 1978, flood. Channel-bed SCour occurred near borrow pits and notably at the bridge crossing where measurements were made as shown in Fig. 3 for Section 51. Deposition was observed in the borrow pits. With limited flood discharge and duration, these borrow pits were only partially refilled. Major changes in the river channel occurred during the greater Feb- ruary, 1980, flood. These changes included channel-bed aggradation and degradation, width variation, and lateral migration of the channel as described below. These changes were recorded by photographs taken during the flood, by a high water mark at Section 52, and by channel- bed measurements at selected cross sections after the flood as shown in Fig. 3. Major aggradation occurred in the borrow pits as they were largely refiJled after the flood. Major degradation occurred near the borrow pits and at the bridge crossing during the flood. Failure of several bridge piers as shown in Fig. 4 was caused by channel-bed scour, high velocity, and debris accumulation on the piers. Channel-bed aggradation and' degradation were accompanied by changes in channel width. The initial channel width was highly uneven along the reach primarily due to width encroachment by road embank- ments at the bridge crossing. Sand mining also contributed to the initial uneven width variation. As shown in Fig. 3, changes in channel width that occurred during the flood consisted of widening at the bridge cross- ing (Section 51) and other initially narrow sections (Sections 47, 49, 50, 57, 58, 59) and reductions in width at initially wide sections, notably at FIG. 4.-$an DIeguItO River Near Via de Santa Fa Road on February 21, 1980 (Looking Toward South) 164 13