Friction Factors in Open Channels: Progress Report of the Task Force on Friction Factors in Open Channels of the Committee on Hydromechanics of the Hydraulics Division

The development of fixed-bed, open-channel flow resistance equations is traced from Chezy to the present (1963). The use of the Darcy-Weisbach f is recommended, and methods of determining f are examined. Manning's n is also useful but has limitations that are explained. It gives good results for fully rough flow and smooth channel flow but is less satisfactory in the transition range. The relationship of boundary layers to open-channel resistance must be studied in order to advance the understanding of frictional resistance in open channels. Movable bed channel resistance and the criteria for determining when bed motion begins are reviewed. Further research is recommended in various areas such as definition of equivalent roughness, transition from smooth to fully rough flows for different types of roughness, large relative roughness, composite channels, and resistance with movable beds. The report concludes with a comprehensive bibliography through 1960.