UPPER-REGIME PLANE BED

The analysis of a laboratory and field data set for sand-bed channels defines the characteristics of upper-regime plane bed with sediment tr ansport. The occurrence of upper-regime plane bed relates to the lamin ar sublayer thickness delta and depends on shear velocity u, median g rain size d(50) and grain shear Reynolds number R. Two different boun dary conditions are recognized: (1) Transition to hydraulically smooth when R < 11.6; and (2) transition to hydraulically rough when R* > 1 1.6. In the first case, upper-regime plane bed is obtained when u(2) congruent to g delta, where g is the gravitational acceleration. In th e second case, upper-regime plane bed is observed when d(50) congruent to 2 delta. Temperature effects are possible when R approaches 11.6, which explains the observations on the Missouri River. Resistance to flow for plane bed with sediment transport increases with the Shields parameter.