!*==sbzdisp.spg  processed by SPAG 6.70Rc at 15:33 on 10 Dec 2012
!*------------------   SPAG Configuration Options   --------------------
!*--0323,76 000101,-1 000000102011332010100002000000210211210,136 10 --
!*--1100000011112111000000000000,10,10,10,10,10,10,900,100 200000000 --
!*--000000010000000000000,72,72 73,42,38,33 00011112110000100000000  --
!*----------------------------------------------------------------------
!++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
!$Author: joelevin $
!$Date: 2011-03-24 11:33:26 -0500 (Thu, 24 Mar 2011) $
!$Revision: 11724 $
!$HeadURL: https://eweru-dev1.eweru.ksu.edu/svn/code/weps1/branches/WEPS_F90_update/weps.src/src/lib_erosion/sbzdisp.for $
!**********************************************************************
! subroutine sbzdisp
!**********************************************************************
      subroutine sbzdisp(szrgh,bcxrow,bc0rg,wzoflg,&bdrlai,bdrsai,bbzht,&
                       & bcrlai,bcrsai,bczht,&awzdisp,wzdisp)
      use i_p1unconv
      use s_biodrag
      implicit none
!*--SBZDISP20
!
!*** Start of declarations rewritten by SPAG
!
! Dummy arguments
!
      real :: awzdisp,bbzht,bcrlai,bcrsai,bcxrow,bczht,bdrlai,bdrsai,   &
            & szrgh,wzdisp
      integer :: bc0rg,wzoflg
      intent (in) bbzht,wzoflg
      intent (out) awzdisp
      intent (inout) wzdisp
!
! Local variables
!
      real :: bht,bsai
!
!*** End of declarations rewritten by SPAG
!
 
!     +++ PURPOSE +++
!     Calc. zero plane displacement (mm)
 
!     set field zero plane displacement equal to Anemometer zero plane
!     displacement when anem. at the field site, ie. wzoflg = 1
 
      ! using equation from: Raupach, M.R. 1994. Simplified Expressions for
      ! Vegetation Roughness Length and Zero-Plane Displacement as functions
      ! of Canopy Height and Area index. Boundary Layer meteorology 71:211-216.
 
!     +++ ARGUMENT DECLATION +++
 
!     +++ ARGUMENT DEFINITIONS +++
!     szrgh  - ridge height (mm)
!     bcxrow - crop row spacing (m)
!     bc0rg  - flag=0 - crop planted in furrow bottom
!              flag=1 - crop planted on ridge top
!     wzoflg - flag=0 - weather measurements are from a distant station
!              flag=1 - weather measurements are in field
!     bdrlai - residue leaf area index (total)(m2/m2)
!     bdrsai - residue stem area index (total)(m2/m2)
!     bbzht  - composite average residue height (m)
!     bcrlai - crop leaf area index (m2/m2)
!     bcrsai - crop stem area index (m2/m2)
!     bczht  - crop height (m)
!     bc0rg  - flag=0 - crop planted in furrow bottom
!              flag=1 - crop planted on ridge top
!     awzdisp - zero plane displacement at weather location (mm)
!     wzdisp - zero plane displacement at location (mm)
 
!     +++ FUNCTIONS CALLED
 
!     +++ LOCAL VARIABLES +++
 
!     +++ LOCAL VARIABLE DEFINITIONS +++
!     bht   - biomass height (mm)
!     bsai  - biomass silhouette area index
 
!     +++ INCLUDE FILES+++
 
!     +++ PARAMETERS +++
 
!     +++ END SPECIFICATIONS +++
 
      ! calculate "effective" biomass silhouette area index
      bsai = biodrag(bdrlai,bdrsai,bcrlai,bcrsai,bc0rg,&bcxrow,bczht,   &
           & szrgh)
 
      ! find maximum biomass height and convert to mm
      bht = max(bbzht,bczht)*mtomm
 
      ! use silhouette area index and biomass height to find zero plane displacement
      if (bsai>1.0E-10) then
         wzdisp = bht*(1.0-(1.0-exp(-(15.0*bsai)**0.5))&/(15.0*bsai)    &
                & **0.5)
      else
         wzdisp = 0.0
      end if
 
         ! anemom. in field set weather displacement to field displacement
      if (wzoflg==1) awzdisp = wzdisp
 
      end subroutine sbzdisp