The efficient 2D/3D hybrid model developed within this project will combine 2D and 3D numerical models. The hybrid model is an integration of 2D shallow water numerical models and their ability to model large, real domains and numerically demanding 3D Navier-Stokes flow models being more accurate in areas where three-dimensional effects are significant in real engineering practice free surface flow problems. The project consists of two main parts: numerical model development and simulation software creation. The numerical model development starts with the set-up of a 3D model suitable for hybrid model use through analysis of Open Foam VOF and its test comparison with other 3D models: SPH (and other particle methods), SSIIM-3D, SCHISM-3D. Simultaneously, the 2D model of shallow water with parallelization capabilities is being set-up. A hybrid 2D/3D model development meets many numerical challenges but the main focus is on numerical problems at the 2D/3D interface, automatic creation of 3D geometry based on 2D terrain morphology, introduction of boundary layer into 2D model, 2D/3D interface management in case of supercritical or subcritical flow and investigation of possible substitution of 3D model with the machine learning based metamodels (Support Vector Machine). The project idea will develop through the cooperation of scientists from University of Rijeka various faculties, with the scientist from the industry (dr M. Nujic – creator of the most prominent 2D free surface flow simulation software in German-speaking countries) and in cooperation with the TU Munich scientists. The aforementioned collaborative concept is the guarantee of project success in its effort to create state-of-the-art hybrid 2D/3D free surface flow model.