Water is the greatest natural treasure of Serbia. However, this natural treasure is not only for the benefit of the citizens, but it has caused and continues to cause the greatest natural disasters with significant material damage in the country. This paper deals with the methodology of using an unmanned aerial vehicle with an integrated RTK GNSS module, for the purpose of field surveilance by Unmanned Aerial Vehicle (UAV) photogrammetry. Gradually and in detail, the procedures are explained, as well as the use of programs for processing Pix4D, Global Mapper and creating 3D terrain models. A control and presentation of obtained resuls is performed. Based on digital elevation models, for the research area, a flood zone simulation for different levels of the Tisa River is presented.