code: def headloss_fric_rect(FlowRate, Width, DistCenter, Length, Nu, PipeRough, openchannel):
      
      #Checking input validity - inputs not checked here are checked by
      #functions this function calls.
      ut.check_range([Length, ">0", "Length"])
      return (fric_rect(FlowRate, Width, DistCenter, Nu,
                        PipeRough, openchannel)
              * Length
              / (4 * radius_hydraulic(Width, DistCenter, openchannel).magnitude)
              * FlowRate**2
              / (2 * gravity.magnitude * (Width*DistCenter)**2)
              )
docs: Return the major head loss due to wall shear in a rectangular channel.
  
      This equation applies to both laminar and turbulent flows.