Large Basin Deterministic Hydrology: A Case Study

Abstract

A case study of large basin hydrology is performed. The basin is the Santa Cruz River upstream of Cortaro Farms Bridge near Tucson, Arizona, draining 3,503 sq miles. The evaluation uses novel techniques of deterministic hydrologic modeling to calculate frequency‐based floods at proposed bridge improvement sites. A computer model capable of simultaneously handling the complex topology of the basin is driven by 100‐yr frequency National Weather Service rainfall events of 24‐, 48‐ and 96‐hour durations. The model is calibrated using recorded rainfall‐runoff data for the flood of October, 1983, which produced record flows throughout southeastern Arizona. Once calibrated, a series of general and local storms are simulated. General storms cover the entire basin with low‐intensity rainfall events. Local storms cover selected portions of the basin with high intensity rainfall events. Critical peak flows at the bridge sites are shown to be associated with a combination of general 24‐hr and local 48‐hr storms. Regulatory and design discharges are adopted, based on the findings of the computer model.