Velocity Distribution with Dip- phenomenon in Conic Open Channels

Conic open channel flow as occurs in sub-drains, sewers, and culverts is computed by Manning’s or Darcy’s resistance equation only for the average velocity. Yet, fish passage culvert design requires the cross-sectional velocity distribution, which is solved in this research based on two hypotheses: (i) Centreline velocity distribution follows the conventional log-law with a cubic deduction near the water surface; (ii) Cross-sectional velocity distribution is described by Guo and Julien’s modified log-wake-law but neglecting the sine-square function. These hypotheses result in a novel and simple turbulent velocity distribution model without any fitting parameter. Its graphical interpretation for the elliptic, parabolic, and hyperbolic channels indicates reasonable velocity contours with dip-phenomenon. Further, it agrees well with circular pipe data in the average shear velocity, the velocity-dip position, the centreline and cross-sectional velocity distributions. Finally, it is useful for fish passage culvert design by specifying a low velocity zone near the wall.