code: def calc_qm_v1(self):
      
      con = self.parameters.control.fastaccess
      flu = self.sequences.fluxes.fastaccess
      if (flu.am > 0.) and (flu.um > 0.):
          flu.qm = con.ekm*con.skm*flu.am**(5./3.)/flu.um**(2./3.)*con.gef**.5
      else:
          flu.qm = 0.
docs: Calculate the discharge of the main channel after Manning-Strickler.
  
      Required control parameters:
        |EKM|
        |SKM|
        |Gef|
  
      Required flux sequence:
        |AM|
        |UM|
  
      Calculated flux sequence:
        |lstream_fluxes.QM|
  
      Examples:
  
          For appropriate strictly positive values:
  
          >>> from hydpy.models.lstream import *
          >>> parameterstep()
          >>> ekm(2.0)
          >>> skm(50.0)
          >>> gef(0.01)
          >>> fluxes.am = 3.0
          >>> fluxes.um = 7.0
          >>> model.calc_qm_v1()
          >>> fluxes.qm
          qm(17.053102)
  
          For zero or negative values of the flown through surface or
          the wetted perimeter:
  
          >>> fluxes.am = -1.0
          >>> fluxes.um = 7.0
          >>> model.calc_qm_v1()
          >>> fluxes.qm
          qm(0.0)
  
          >>> fluxes.am = 3.0
          >>> fluxes.um = 0.0
          >>> model.calc_qm_v1()
          >>> fluxes.qm
          qm(0.0)