Application of 3D CFD Modeling to Improve Calibration of 2D Hydraulic Model

Successful calibration of model components is a vital step in numerical hydraulic analysis. However, model calibration is a challenging task, especially when there are hydraulic structures within the simulation domain. This paper presents a 2D HEC-RAS modeling case study on the Kissimmee River Restoration project focusing on the backwater effects due to the restoration of the canal and structure system. The 2D model covers about 10-mile of the C-38 Canal system including the flood plain and eight hydraulic control structures (spillways, ship lock, weirs, and levees) in South Florida. Accurate estimation of the discharge capacity of each structure is a critical component of model calibration. However, the presence of several hydraulic structures complicates the process owing to potentially high number of calibration combinations of structure discharge parameters and sub-domain roughness coefficients in the system. Instead of the tedious trial-error approach, this paper applied 3D CFD modeling to directly attain the discharge coefficients for the stage-discharge relationships embedded in 2D HEC-RAS model. At the South Florida Water Management District, CFD has been proven to be a very effective and complimentary tool for flow rating development, especially when available field measurements are limited. The approach presented here provides the technical advantage of obtaining CFD model-based discharge coefficients for hydraulic structures that can bypass the traditional calibration process of the structure’s conveyance capacity, and subsequently can focus on calibration of the roughness of the flood plain and canal system in the 2D hydraulic model.