In this Colorado Department of Transportation project, large debris-flow culverts crossing the new four-lane State Highway 82 near Aspen, Colorado were designed. Along the project site, the highway passes through Snowmass Canyon along a series of small debris-producing watersheds as shown in Figures 1 and 2.

Culvert designs were based on computer modeling results from Federal Highway Administration’s BRI-STARS model. As a part of the project, BRI-STARS model developed earlier by Dr. A. Molinas, Hydrau-Tech, was modified to accommodate debris flows by including various theoretical formulations. Traditional clear-water modeling results in considerably undersized culverts for debris flows; by using BRI-STARS modeling of viscous mudflows, culvert sizes that can pass the design discharges accurately can be computed. In order to widen the existing two-lane highway to four lanes along the narrow canyon, a split configuration was adopted. Space for the additional two lanes going from Glenwood Springs to Aspen, Colorado, were created by encroaching on the canyon wall by building a retaining wall and by elevating the upper lanes by as much as 30 feet. Along the path, at 8 locations basins producing debris fans border the highway. Potential debris flows from these basins are passed beneath the highway as shown in Figure 3 without interrupting traffic. Figure 4 shows the computed debris flow profiles for one of the basins. These flow profiles were generated by the enhanced BRI-STARS model by incorporating a visco-plastic fluid flow component.

Figures 5 and 6 show the elevated section of highway cutting through a debris fan at the base of Basin H.

Figure 7 shows a culvert design that does not require a break in the invert slope for the watershed identified as Basin I due to the location of the crossing. The cast-in-place culvert outlet and typical sections, as well as the construction of elevated sections of the highway are shown in Figures 8 and 9.