Abstract: Composite roughness is a vital input parameter for hydraulic calculations of ice-covered channels. Two general equations for deriving composite roughness coefficient in ice-covered streams, based on the principles of flow continuity or force balance, are presented in this paper. Taking parabolic, rectangular, and trapezoidal under-ice flow sections as the representative geometries, this paper systematically summarizes the assumptions (e. g., equalities of wetter perimeters, subsectional mean velocities, and hydraulic radii) used in the derivation of six formulae:those of Pavlovskiy, Einstein, Lotter, Sabaneev, Larsen and its modified form. Laboratory measurements and field observations were used to examine the performance of those above-mentioned formulae. Comparative results indicated that the modified Larsen formula had the best overall performance and therefore its use is recommended in engineering practice. The first five formulae produced relatively large errors in the prediction of composite roughness of ice-covered streams because the main assumptions of equalities of velocities and hydraulic radii are only valid for few special cases. In particular, care should be taken when using the Lotter and Pavlovskiy formulae because of their underestimation of the composite roughness in high-grade asymmetric channels.