The diploma thesis deals with determining the discharge coefficient of thin-walled weirs with a triangular notch installed at the end of a circular pipe (channel with a semicircular cross-section). Experimental measurements were carried out under laboratory conditions to determine the discharge coefficient. The measurements were performed for four different notch angles and two pipe diameters. Based on the measured data, the discharge coefficient was calculated using relationships derived from Bernoulli’s equation. The calculated values were then processed graphically to assess the dependence of the discharge coefficient on the observed parameters and on the relative filling of the pipe. Subsequently, an analysis of approximation curves was performed to describe the course of these dependencies and to evaluate the suitability of the individual relationships. The results made it possible to assess the influence of the examined parameters on the value of the discharge coefficient.