Overtopping Protection for A.R. Bowman Dam

Arthur R. Bowman Dam is a central-core rockfill dam located on the Crooked River in central Oregon (fig. 1). The structural height is 245 feet and the crest length is approximately 800 feet. The probable maximum flood (PMF) overtops the dam by 20 feet with a peak unit discharge of 280 ft3/s over the embankment crest. Overtopping begins at 23 percent of the PMF. Twenty-three percent of the PMF corresponds to approximately the 500-year flood.

Overtopping protection has been chosen as the modification to accommodate large flood events. The overtopping protection will consist of a continuously reinforced concrete deck placed over the entire downstream face similar to the upstream facings currently used on concrete faced rockfill dams. The continuously reinforced concrete slope protection provides an economically competitive modification that offers technical advantages over more commonly used slope protection alternatives. The continuous reinforcing provides monolithic behavior, controls crack openings, and eliminates crack offsets to create a nearly impervious barrier without protrusions into the flow. Other design features discussed include drainage, groin protection, crest details, and accommodating fluctuating pressures in the hydraulic jump region.