Open channel flow rate was determined by using the radiotracer balance method (RBM). The magnitude of errors arising from the scattering was investigated in the study. An open channel experimental system was set up in the laboratory. For the experiments Na-24 was used, which was irradiated in the TRIGA Mark-II Training and Research Reactor. Error evaluation observed whether the scattering effect with modification of the calibration factor could improve the results. (C) 2002 Elsevier Science Ltd. All rights reserved.