The affect of the Reynolds number on the characteristics of the coherent structures in a flume was studied for Reynolds numbers Re-theta = 300, 470, 690 and ratio of channel width to water depth from 6.4 to 3.4.Infrared thermography was used to detect the coherent structures, which originate in the buffer region and which were heated there, as they arrive at the water interface. It was shown that large scale turbulent structures are ejected from the buffer region toward the free surface, where they can be detected as hot spots. The frequencies of the bursting of the coherent structure were detected by temperature VITA technique, and by counting the spots on the free interface per unit time.