code: def calc_qvr_v1(self):
      
      con = self.parameters.control.fastaccess
      flu = self.sequences.fluxes.fastaccess
      for i in range(2):
          if (flu.avr[i] > 0.) and (flu.uvr[i] > 0.):
              flu.qvr[i] = (con.ekv[i]*con.skv[i] *
                            flu.avr[i]**(5./3.)/flu.uvr[i]**(2./3.)*con.gef**.5)
          else:
              flu.qvr[i] = 0.
docs: Calculate the discharge of both outer embankments after
      Manning-Strickler.
  
      Required control parameters:
        |EKV|
        |SKV|
        |Gef|
  
      Required flux sequence:
        |AVR|
        |UVR|
  
      Calculated flux sequence:
        |QVR|
  
      Examples:
  
          For appropriate strictly positive values:
  
          >>> from hydpy.models.lstream import *
          >>> parameterstep()
          >>> ekv(2.0)
          >>> skv(50.0)
          >>> gef(0.01)
          >>> fluxes.avr = 3.0
          >>> fluxes.uvr = 7.0
          >>> model.calc_qvr_v1()
          >>> fluxes.qvr
          qvr(17.053102, 17.053102)
  
          For zero or negative values of the flown through surface or
          the wetted perimeter:
  
          >>> fluxes.avr = -1.0, 3.0
          >>> fluxes.uvr = 7.0, 0.0
          >>> model.calc_qvr_v1()
          >>> fluxes.qvr
          qvr(0.0, 0.0)