Trout Creek Dam

Challenges

Trout Creek Dam is a large, high-hazard dam located just south of Buena Vista, Colorado.  The 70-foot-high roller-compacted concrete (RCC) dam impounds about 670 acre-feet (ac-ft).  The dam includes a service spillway designed to pass the 100-year flood event.  The existing service spillway is a controlled overflow section located near the center of the dam.  For floods greater than the 100-year event, the entire RCC dam is overtopped.  The owner proposed to raise the dam and existing service spillway by 15 feet to increase the storage capacity by about 485 ac-ft.  Technical challenges associated with raising the dam included ensuring the existing dam remained stable with the increased loads, developing an effective connection detail to avoid overstressing the existing RCC dam, and developing water-tight connections along the high-fractured rock abutments.

Solution

RJH initially developed concepts to raise the existing dam and service spillway with the structures being raised as ogee-shaped weirs.  The ogee weirs were sized to pass the Probable Maximum Flood (PMF).  Conveying the PMF would have also required raising an existing saddle dike by about 8 feet.  RJH worked closely with the Colorado Office of the State Engineer to obtain approval for an inflow design flood with a 10,000-year return period.  The reduction in inflow design flood accommodated raising the existing dam and spillway as broad-crested weirs instead of the more complicated ogee shape that was initially anticipated. This also only required raising the existing saddle dike by one foot.

RJH is currently designing the modifications.  RJH is using a three-dimensional finite analysis model to evaluate the static and seismic stress in the enlarged dam, and to support design of the connection between the existing and new dam.