def vel_grad_avg(self):
        """Calculate the average velocity gradient (G-bar) of water flowing
        through the flocculator.
        :returns: Average velocity gradient (G-bar)
        :rtype: float * 1 / second
        """
        return ((u.standard_gravity * self.HL) /
               (pc.viscosity_kinematic(self.temp) * self.Gt)).to(u.s ** -1)
Calculate the average velocity gradient (G-bar) of water flowing
        through the flocculator.
        :returns: Average velocity gradient (G-bar)
        :rtype: float * 1 / second