Author(s): Yajayra Diaz; Michael A. Phillips; Brian M. Crookston
Linked Author(s): Brian Crookston
Keywords: Labyrinth weir; spillway; flip bucket; energy dissipator; submerged bucket; scour; erosion
Abstract: Prado Dam, located in southern California, is an earth-fill embankment dam with a gated outlet works and a reinforced concrete spillway. A project is currently underway to design modifications to the spillway to address deficiencies associated with capacity and hydraulic performance. The existing spillway was originally designed for a maximum discharge of approximately 5,000 m3/s. A revised hydrologic analysis has estimated the new probable maximum flood (PMF) design discharge has more than tripled to approximately 17,400 m3/s. The major features of the spillway modifications include construction of a new labyrinth weir control structure, raising the spillway crest 6.1 m, constructing new weir walls, embankment connections, chute walls and chute slabs while using the existing flip bucket. Due to the poor quality of the foundation material at the site, the existing flip bucket is supported by a 24-meter-deep crib wall structure making its replacement structurally challenging. Therefore, a study was conducted to determine the expected performance of the existing flip bucket for a range of floods up to the new PMF event. This paper focuses on two main issues that were evaluated using empirical calculations derived from limited available research data, Computational Fluid Dynamics (CFD) modelling, and results from a 1:38 scaled physical model study conducted at the Utah State University Water Research Laboratory. These are: (1) the existing flip geometry and its adequacy for dissipating energy for the revised design discharge and (2) the maximum scour potential downstream of the flip bucket due to high tailwater conditions that effectively submerges the flip bucket. This paper also provides a comparison of the estimated erosion patterns and maximum scour potential downstream of the submerged flip bucket, highlighting complimentary strength of these three modelling tools and the connectivity needed between research and practice to meet climatic challenges and resolve dam safety concerns.
DOI: https://doi.org/10.3929/ethz-b-000675921
Year: 2024