This paper presents experimental results concerned with the overall resistance and boundary shear in circular conduits flowing part full, with and without a flat bed, simulating a hydropower tunnel or deposited sediments in a sewer. The importance of flow resistance in determining the stage-discharge curve is examined in detail. This paper illustrates that Manning's n is invariant with Stage and, as a consequence, an empirical relationship based on Manning's formula can be established which allows the prediction of a non-dimensional stage-discharge curve. When the conduit is running part full, there is strong evidence of secondary flows being present, based on distortions in the isovel patterns and in the lateral distributions of boundary shear stress. The overall frictional resistance is shown to be larger for subcritical flow than for supercritical how over the range of Reynolds numbers tested.