Page - 71 - in Book of Full Papers - Symposium Hydro Engineering

of the upper chute replaced the following year, during the 2018 construction season.  The eroded scour holes in the FCO Spillway lower chute should be filled with roller-compacted concrete (RCC) to restore the eroded spillway rock foundation (see Fig. 4). The damaged concrete chute walls and invert panels in the lower chute should also be removed, and new structural-concrete sections (chute slabs/panels and walls) should be constructed to modern standards for the entire lower chute. If the entire lower chute could not be restored by November 1, 2017, the construction work should be sequenced to defer backfilling of the initial scour hole in order to use the scour hole and the erosion channel to convey spillway discharges from the upper chute to the Feather River. These measures were accepted by DWR management and an Independent Board of Consultants in mid-March 2017 and designs were initiated immediately. During the design and 2017 (Phase 1) construction phases, the limits for specific measures on both the upper and lower chutes were modified several times as a result of improved understandings of the work involved, various constraints, and what the construction contractors could accomplish during the very abbreviated 2017 construction season. The alternative measures finally adopted for repair and replacement of the upper and lower chutes, during the 2017 and 2018 construction seasons, are illustrated in Fig. 5 and Table 1. Fig. 4 Conceptual cross section for reconstructing the eroded the FCO Spillway lower chute using Roller Compacted Concrete in 2017 71