When creating models of hydrotechnical structures and studying phenomena occurring in open channels, the selection of appropriate similarity criteria plays a crucial role. Laboratory tests on models are an effective method for verifying variants of solutions for the outfall, fortifications and the entire system of the tailwater of damming structures. However, the development of models is accompanied by a number of challenges and factors that, if not considered, affect the obtained results validity. This study demonstrates to summarize the hazardous factors accompanying the hydraulic modelling researches and proposals for their mitigative solutions met during ten years practice in laboratory works. Each identified problems is described in a separate section. Stage of identified problems occurrence was also given, as well as dedicated solutions. This results in a set of good practice advices formulation for further hydraulic modelling investigations. Model studies enable project optimization by testing different configurations and parameters without the need to build full-scale structures or installations. Moreover hydraulic systems will react to various factors in the future, which can be helpful in planning and forecasting.