Composite roughness of ice-covered flows in open channels

The composite roughness of the ice covered flow is a key parameter to determine the relation-ship between the flow and water stage. This paper presents a generalized formula for the composite rough-ness of ice covered flows by analyzing the relationship among Manning roughness,section-averaged watervelocity and wetted perimeter. Based on the generalized formula,the influence of the velocity coefficient aon the composite roughness of the ice covered flows in rectangular channels is studied by considering thedistribution of water velocities. Meanwhile,in order to understand the scope of application to them,Ein-stein formula,Belokon- Sabaneev formula and Larsen formula are compared with the generalized formulasystematically. The results show that for the rectangular open channal with small kreadth-depth ratio b/H,the composite roughness computed by Einstein formula approximate closest to that by the generalized formu-la,and the composite roughness obtained by both Belokon- Sabaneev formula and Larsen formula deviatefor from that by the generalized formula in many cases.