Page - 91 - in Book of Full Papers - Symposium Hydro Engineering

o “Fill the Hole with RCC” – This concept, shown in Fig. 3, anticipated using horizontal lifts of RCC to fill a portion of the eroded hole sufficient to re-construct the FCO Spillway chute to the original geometry. Fig. 3 Initial Sketch of RCC for "Fill the Hole" Solution The following list of arguments, in support of the “Fill the Hole with RCC” approach, was presented to the OER Spillway Task Force, including regulatory agencies and the independent Board of Consultants for consideration: 1. The recommended alternative would provide the least risk to DWR by reconstructing the damaged portion of the FCO Spillway chute back to the original geometry with the foundation restored using RCC. 2. Reconstructing the FCO Spillway chute to its original geometry would have the least unknowns regarding hydraulic performance, which had already been studied, modeled, and proven through years of service, including: a) the least amount of additional field investigations or hydraulic modelling; and b) the avoidance of further negative impacts on flow patterns and debris in the diversion pool (Feather River) downstream of the spillways. 3. The use of RCC would allow the reuse of scoured rock debris recovered from Feather River as well as rock excavated from the chute foundation as concrete coarse and fine aggregates. 4. Reconstructing the FCO Spillway chute to its original design configuration would have the least environmental impact as no new areas will be permanently impacted. 5. The use of RCC for dams and spillways is mature in the dam engineering profession and construction industry and has been shown to be a highly efficient methodology for accelerated construction as opposed to conventional mass or reinforced concrete. 6. There have been several high-volume RCC projects for dams of this magnitude in the State of California over the last 10 years; thus, this RCC alternative will provide highly-reliable cost estimates and experienced contractors. 91