Investigating the Effect of Changes of the Roughness Coefficient on the Results of Model Calculations in One-dimensional Hydraulic Models

One of the key elements in describing the flow of floodwaters is to determine the resistance created by friction acting along the surface wetted by water and created by objects directly washed by water. Flow resistance (roughness) influences flow velocity, water level, and, consequently, the river's capacity (Aberle 2020). This paper analyses the effect of the manner of defining roughness coefficients in one-dimensional models on the stability of these models and the results of model calculations. Three methods of defining the transverse variation of roughness coefficient in cross sections were used in the model calculations: Distributed, High/Low Flow Zones and Uniform. The greatest model stability, the highest flow rate values and the lowest water table ordinates were obtained when Distributed was selected. This has a major impact on determining the extent of flood hazard zones.