anchor.diff:          md%domains(1)%boundary_subroutine => flather_boundary
       case('flather_with_vh_equal_zero')
           md%domains(1)%boundary_subroutine => flather_boundary
  +    case('boundary_stage_radiation_momentum')
  +        md%domains(1)%boundary_subroutine => boundary_stage_radiation_momentum
       case default
           stop "Invalid boundary_type value"
       end select
  
positive.code:             case('boundary_stage_transmissive_momentum')
                  ! Do nothing, because we do not need uh/vh.
                  stage_uh_vh_elev(2:3) = 0.0_dp 
  
              case('flather_with_vh_equal_zero') 
                  ! This absorbs, but also distorts the stage at the boundary too much when
  
negative.code:             stage_uh_vh_elev(2:3) = 0.0_dp
          else
  
              ! Much experimentation was conducted here. This problem is sensitive to
              ! imperfections in our semi-transmissive boundary conditions which allow a 
              ! stage forcing. (Not too surprising, because the boundary is quite close to the
              ! coast, in 'not very deep' water).
  