25 years of Labyrinth Spillways From Ute to Dog River: Notes from the Field

Abstract Only - In 1981, the US Bureau of Reclamation proposed a labyrinth spillway for the modification of Ute Dam. This labyrinth, though not the first constructed in the United States, was notable because it was the largest labyrinth constructed at that time, had the highest discharge capacity of 550,000 cfs, and had significant cost savings compared with other overflow and gated spillway alternatives,. But most importantly, the hydraulic model studies of Ute Dam lead to the development of generalized methods for design of labyrinth weirs. This information fueled the use of labyrinths as an economical spillway for use at new dams and to increase spillway capacity at existing dams.
In 2003, Falvey’s book, “Hydraulic Design of Labyrinth Weirs,” assessed the various generalized methods being used for design of labyrinth weirs. Since then additional issues have been raised concerning labyrinth spillway design. Currently, the Dog River Dam labyrinth spillway, constructed in the early 1990’s is being raised from 15 feet to 25 feet to provide additional storage. Hydraulic model study results of this raise in wall height have prompted a reassessment of the parameters that affect the generalized labyrinth design methods including some of the opinions expressed in Falvey’s book.
The authors have been involved in the design and construction of over 25 labyrinth spillway projects including Ute Dam and Dog River Dam, the latest challenge. Their labyrinth experience ranges from 18-inch high stainless steel labyrinths with a one-foot design head to labyrinths with 30-foot high concrete walls and design heads of nearly 20 feet. The focus of this paper will be on best practices for design, construction and operation of labyrinth spillways based upon the author’s experience. Specific issues to be presented include:
- Low flow conditions regarding discharge and crest shape
- Vertical aspect ratio, W/P, and its interrelation with nappe interference
- Definition of crest length and its implications on past model study results.
- Abutment effects and upstream apex influences
- Crest shape efficiency versus construction means
- Labyrinth wall construction issues
- Operational considerations including waves, minimum flow releases and recreation