def V_Manning(Rh, S, n):
    """Predicts the average velocity of a flow across an open channel of
    hydraulic radius Rh and slope S, given the Manning roughness coefficient
    n.

    Flow rate is given by:

    .. math::
        V = \\frac{1}{n} R_h^{2/3} S^{0.5}

    Parameters
    ----------
    Rh : float
        Hydraulic radius of the channel, Flow Area/Wetted perimeter [m]
    S : float
        Slope of the channel, m/m [-]
    n : float
        Manning roughness coefficient [s/m^(1/3)]

    Returns
    -------
    V : float
        Average velocity of the channel [m/s]

    Notes
    -----
    This is equation is often given in imperial units multiplied by 1.49.

    Examples
    --------
    Example is from [2]_, matches.

    >>> V_Manning(0.2859, 0.005236, 0.03)
    1.0467781958118971

    References
    ----------
    .. [1] Blevins, Robert D. Applied Fluid Dynamics Handbook. New York, N.Y.:
       Van Nostrand Reinhold Co., 1984.
    .. [2] Cengel, Yunus, and John Cimbala. Fluid Mechanics: Fundamentals and
       Applications. Boston: McGraw Hill Higher Education, 2006.
    """
    return Rh ** (2 / 3.0) * S ** 0.5 / n
