code: def calc_rk_v1(self):
      
      con = self.parameters.control.fastaccess
      der = self.parameters.derived.fastaccess
      flu = self.sequences.fluxes.fastaccess
      if (flu.ag > 0.) and (flu.qref > 0.):
          flu.rk = (1000.*con.laen*flu.ag)/(der.sek*flu.qref)
      else:
          flu.rk = 0.
docs: Determine the actual traveling time of the water (not of the wave!).
  
      Required derived parameter:
        |Sek|
  
      Required flux sequences:
        |AG|
        |QRef|
  
      Calculated flux sequence:
        |RK|
  
      Basic equation:
        :math:`RK = \\frac{Laen \\cdot A}{QRef}`
  
      Examples:
  
          First, note that the traveling time is determined in the unit of the
          actual simulation step size:
  
          >>> from hydpy.models.lstream import *
          >>> parameterstep()
          >>> laen(25.0)
          >>> derived.sek(24*60*60)
          >>> fluxes.ag = 10.0
          >>> fluxes.qref = 1.0
          >>> model.calc_rk_v1()
          >>> fluxes.rk
          rk(2.893519)
  
          Second, for negative values or zero values of |AG| or |QRef|,
          the value of |RK| is set to zero:
  
          >>> fluxes.ag = 0.0
          >>> fluxes.qref = 1.0
          >>> model.calc_rk_v1()
          >>> fluxes.rk
          rk(0.0)
  
          >>> fluxes.ag = 0.0
          >>> fluxes.qref = 1.0
          >>> model.calc_rk_v1()
          >>> fluxes.rk
          rk(0.0)