A study on the design of highway cross culverts in an area of potential debris flow along the Snowmass Canyon segment of SH-82 in Colorado is presented. Considering the characteristics of the drainage network and the highway cross culverts, FHWA’s BRI-STARS model is enhanced to simulate surface profiles for debris flows. Appropriate sizing of highway cross culverts is provided on the basis of the results of the model simulations for various approaches utilizing both clear-water and debris flow techniques. It is shown that the traditional clear-water modeling results in considerably undersized culverts for debris flows. The modified BRI-STARS model was verified using field data and was shown to be an effective tool in the design of cross culverts to pass debris flows across highways.