subroutine tranb21(utot      ,d50       ,d90       ,h         ,par       , &
                & sbot      ,ssus)
!----- GPL ---------------------------------------------------------------------
!                                                                               
!  Copyright (C)  Stichting Deltares, 2011-2017.                                
!                                                                               
!  This program is free software: you can redistribute it and/or modify         
!  it under the terms of the GNU General Public License as published by         
!  the Free Software Foundation version 3.                                      
!                                                                               
!  This program is distributed in the hope that it will be useful,              
!  but WITHOUT ANY WARRANTY; without even the implied warranty of               
!  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the                
!  GNU General Public License for more details.                                 
!                                                                               
!  You should have received a copy of the GNU General Public License            
!  along with this program.  If not, see <http://www.gnu.org/licenses/>.        
!                                                                               
!  contact: delft3d.support@deltares.nl                                         
!  Stichting Deltares                                                           
!  P.O. Box 177                                                                 
!  2600 MH Delft, The Netherlands                                               
!                                                                               
!  All indications and logos of, and references to, "Delft3D" and "Deltares"    
!  are registered trademarks of Stichting Deltares, and remain the property of  
!  Stichting Deltares. All rights reserved.                                     
!                                                                               
!-------------------------------------------------------------------------------
!  $Id: tranb7.f90 5717 2016-01-12 11:35:24Z mourits $
!  $HeadURL: https://svn.oss.deltares.nl/repos/delft3d/tags/6686/src/utils_gpl/morphology/packages/morphology_kernel/src/tranb7.f90 $
!!--description-----------------------------------------------------------------
!
! computes sediment transport according to
! Nino & Garcia (1998)
!
!!--pseudo code and references--------------------------------------------------
! NONE
!!--declarations----------------------------------------------------------------
    use precision
    implicit none
!
! Call variables
!
    real(fp)               , intent(in)  :: d50     ! grain size diameter (first specified diameter)
    real(fp)               , intent(in)  :: d90     ! grain size diameter (first specified diameter)
    real(fp)               , intent(in)  :: h       ! water depth
    real(fp)               , intent(out) :: sbot    ! bed load transport
    real(fp)               , intent(out) :: ssus    ! suspended sediment transport
    real(fp)               , intent(in)  :: utot    ! flow velocity
    real(fp), dimension(30), intent(in)  :: par     ! sediment parameter list
!
! Local variables
!
    real(fp)       :: a
    real(fp)       :: ah
    real(fp)       :: alf1
    real(fp)       :: beta   ! lowest level of integration interval over vertical
    real(fp)       :: ca
    real(fp)       :: del
    real(fp)       :: dstar
    real(fp)       :: fc
    real(fp)       :: ff     ! coriolis coefficient
    real(fp)       :: ag     ! gravity acceleration
    real(fp)       :: psi
    real(fp)       :: rhosol ! density of sediment
    real(fp)       :: rhowat ! density of water
    real(fp)       :: rksc
    real(fp)       :: rmuc
    real(fp)       :: rnu    ! laminar viscosity of water
    real(fp)       :: t      ! dimensionless relative shear stress
    real(fp)       :: tbc
    real(fp)       :: tbce
    real(fp)       :: tbcr
    real(fp)       :: thetcr
    real(fp)       :: ustar
    real(fp)       :: ws     ! settling velocity
    real(fp)       :: zc
    real(fp)       :: mud_d  ! dynamic friction coefficient, default  = 0.23.
    real(fp), external :: shld
!
!! executable statements -------------------------------------------------------
!
    sbot = 0.0_fp
    ssus = 0.0_fp
    !
    ag     = par(1)
    rhowat = par(2)
    rhosol = par(3)
    del    = par(4)
    rnu    = par(5)
    !
    rksc  = par(11)
    mud_d = par(12)  
    !
    if (h/rksc<1.33_fp .or. utot<1.e-3_fp) then
       return
    endif
    !
    a     = rksc
    dstar = d50*(del*ag/rnu/rnu)**(1.0_fp/3.0_fp)
    !
    rmuc   = ( log10(12.0_fp*h/rksc) / log10(12.0_fp*h/3.0_fp/d90) )**2
    fc     = 0.24_fp * (log10(12.0_fp*h/rksc))**( - 2)
    tbc    = 0.125_fp * rhowat * fc * utot**2
    tbce   = rmuc * tbc
    thetcr = shld(dstar)
    tbcr   = (rhosol-rhowat) * ag * d50 * thetcr
    sbot   = sqrt(ag*del*d50) * d50 * (12.0_fp/max(mud_d, 0.0_fp)) * (tbce-tbcr) * (tbce**(0.5_fp)-0.7_fp*tbcr**0.5_fp) / rhosol ! [m2/s]
end subroutine tranb21