^{a}, Stuart Cameron, Mark Stewart and Vladimir Nikora

^{a}andrea.zampiron@abdn.ac.uk

In open-channel flows, one of the main assumptions is of fully developed flow, which means that flow parameters do not change in the streamwise direction. The question then is: what distance from the flume entrance is required to achieve fully developed flow conditions? The available data are not sufficient to answer this question properly, and researchers often employ some rather intuitive approximations instead of tailored preliminary measurements. This paper assesses the development of the flow in two different facilities using a combination of stereoscopic particle-image velocimetry and acoustic Doppler velocimetry data sets covering a range of flow conditions and bed roughness. It is found that while some turbulence features are essentially fully developed within 100 flow depths (H) from the channel entrance (i.e., mean velocity, Reynolds stresses, and large-scale motions), others require distances up to 150H (i.e., streamwise turbulent variance and very large-scale motions).