The Bighorn Fire in the Santa Catalina Mountains north of Tucson, Arizona has burned more than 119,000 acres. The burning area has moderate and steep hill slopes, and some are very close to residential areas. These natural conditions poise a high risk of debris flow in the major drainage channel, CDO wash. We applied HEC-RAS sediment transport model to simulate sediment transport processes for quantifying the total sediment load, deposition and erosion volume, and scour depth at bridges in the CDO wash. Sediment samples were collected to obtain sediment size distribution along the reach. During flow events, sediment load were collected using bed load trap and sediment sampler. These data were used to examine the applicability of sediment transport equations in the study reach. The simulation reach is 18.4 mile long with five bridges: East Golder Ranch, Oracle Road, 1st Ave, E Pucsh Ridge, and La Canada Road. All the sediment equations implemented in HEC-RAS model were applied. However, sediment equations primary for sandy rivers including Laursen, Yang, and Ackers-White equations failed the model. The rest equations, Toffaleti, Engelund-Hansen, Meyer-Peter-Muller (MPM), MPM-Toffaleti, and Wilcock-Crowe, yielded reasonable results. But, the results are not consistent with each other. The limited field data is not sufficient for verifying the modeling results. Based on the current results, the upper and lower CDO reaches may have experience up to 6-8 ft erosion in a 100-year storm event.
