Q by sum of conveyances underestimates the frictional contribution from steep segments. Q by composite n overestimates the effect of wide shallow (overbank) friction on flow in deeper areas (main channel).
D50 Values
The Strickler D50 is the size (for a straight and clean channel) implied by the roughness entered. The other D50 results are required to resist erosion per 1) Maricopa County and Robinson Rock Chutes, 2) Maynord, Ruff, and Abt (1989), and 3) Searcy (1967)