Measuring the speed of water in open watercourses is crucial for flow analysis, water resource management, and protection against floods and erosion. In this paper, various methods of measuring water speed are examined, including both traditional and modern techniques. The advantages and disadvantages of each method, as well as their practical applications, are analyzed. The paper's focus is the Brajda watercourse in Rijeka, where measurements of channel geometry and flow velocity were conducted at two locations: Brajda Weir and the channel in front of the Children's Home. The comparison between calculated and measured flows revealed a difference of 7% at the channel in front of the Children's Home and 12.7% at the Brajda Weir, indicating the need for further calibration of the calculation methods. The study also considers methods for collecting data on channel geometry and the process of constructing flow rating curves. Analysis of results obtained with the ADCP device suggests the need for optimization of measurement and flow calculation methods.