Author(s): Michael A. Phillips; Brian M. Crookston; Julie Allen

Linked Author(s): Brian Crookston

Keywords: Labyrinth; weir; hydrodynamic pressures; Fast-Fourier Transform; nappe instability

Abstract: The U.S. Army Corps of Engineers has completed the design of a unique labyrinth weir spillway at Prado Dam, located in Los Angeles, California, USA. The proposed labyrinth weir would consist of an arced configuration, 7-cycles, with varying weir wall height from 8.5 m to 12.5 m with upstream head over the weir cycles of up to 10 m. This hydraulic structure would provide critical flood protection with a spillway capacity for the revised Probable Maximum Flood estimates of up to 17,800 m3/s. Previous research has demonstrated that high head labyrinth weirs can experience significant fluctuating negative pressures at the weir wall resulting in hydrodynamic loads that should be considered during structural design. A Froude similitude model of one of the proposed labyrinth cycles was constructed at 1:14 geometric scale to measure static and dynamic pressures on the weir walls to calculate the potential hydrodynamic loads for select reservoir levels. The results of these physical model tests showed that the maximum hydrodynamic loads (negative pressures on downstream weir wall face) at the crest were approximately 2 to 3 times the upstream head, or -4.6 m to -5.5 m, and surging of the nappe that resulted in large pressure spikes. This paper describes the need to rehabilitate the Prado Dam, the physical model used to inform design decisions, the observed nappe behaviours, the static and dynamic pressure results, and a comparison of the data to assist in the structural design of labyrinth weirs.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024