Boyd Lake Spillway-An Innovative Approach to Using a Labyrinth Weir

Boyd Lake Dam is a Class I facility located in Loveland, Colorado, about 60 miles north of Denver. The dam is owned and operated by the Greeley and Loveland Irrigation Company (Company) and holds over 48,800 acre-feet of storage and the surface area is about 650 acres. The dam was originally constructed in the early 1900’s. A small emergency spillway, constructed along the east side of the reservoir, has since been filled. The Company was faced with the challenge of meeting different spillway discharge requirements from multiple authorities. The Colorado State Engineer’s Office (SEO) requires that existing Class I dams contain spillways that are capable of discharging 75-percent of the Probable Maximum Precipitation (PMP) storm event. The City of Loveland (City) requires a spillway that can handle the 100-year, 2-hour storm. In many areas this would not present a major challenge since a single spillway or a primary and emergency spillway would like satisfy these requirements. In an urban area, however, this can be a major challenge, especially where only two feet of freeboard is available and when the City wants the 100-year storm directed into an existing channel or irrigation canal to avoid impacts to the downstream floodplain. Boyle Engineering Corporation was retained by the Company to provide a solution. In order to meet these requests, a labyrinth spillway with notches cut in half of the cycles was designed. A labyrinth spillway with 59 cycles, capable of discharging 42,710 cfs, was used to meet SEO requirements and serve as the emergency spillway. Notches, 6-inches deep by 30-inches wide, were cut in 30 of the 59 cycles to serve as the primary spillway and allow the 100-year storm event to be released from the reservoir directly into the existing irrigation canal at a low enough flow that the canal would be able to carry it. This paper will further detail and discuss the obstacles faced and how they were overcome using a labyrinth weir. 11 pp., 9 figures, 4 references.