c**********************************************************************
c     subroutine sbwusv
c**********************************************************************
      subroutine sbwusv
     i(brlai, brsai, anemht, awzzo, awu, wzzov,
     o wusv, wus)
c
c     +++ PURPOSE +++
c     to calculate friction velocity above and below the vegetation
c     canopy. Ref. Trans ASAE 31(3):769-775
c
c     +++ ARGUMENT DECLATION +++
      real*4 brlai, brsai, anemht, awzzo, awu, wzzov, wusv, wus
c
c     +++ ARGUMENT DEFINITIONS +++
c     brlai - total leaf area index (m2/m2)
c     brsai - total stem silhoutte area index (m2/m2)
c     anemht- parameter, station anemometr height (m)
c     awzzo - parameter, station aerodynamic roughness length (mm)
c     awuz  - input windspeed driving the EEROSION submodel (m/s)
c     wzzov - aerodynamic roughness length of canopy (mm)
c     wusv  - friction velocity above canopy (m/s)
c     wus   - friction velocity above soil surface(m/s)
c
c     +++ LOCAL VARIABLES +++
      real*4 brcd
c
c     +++ SUBROUTINES CALLED +++
c     sbwus
c
c     +++ END SPECIFICATION +++
c
c     calculate friction velocity above canopy
      call sbwus
     i(anemht, awzzo, awu, wzzov,
     o wusv)
c
c     calculate "effective" biomass drag coefficient
      brcd = brlai*(0.2 - 0.15*exp(-8.*brlai)) + brsai
c
c     calculate friction velocity below canopy
      wus   = wusv * (0.86*exp(-brcd/0.0298) +0.25*exp(-brcd/0.356))
c
c     temp out code
      return
      end
c++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++