c$Author: fredfox $
c$Date: 2001-07-03 19:00:03 $
c$Revision: 1.1.2.1 $
c$Source: /weru/cvs/weps/weps.src/hydro/unsatcond_bc.for,v $
      real*4 function unsatcond_bc(theta, thetar, thetas, ksat, lambda)
c     returns the unsaturated hydraulic conductivity in meters per second as 
c     defined by the Books and Corey function and the Mualem conductivity model

c*** Argument declarations ***
      real*4  theta, thetar, thetas, ksat, lambda

c     theta      - present volumetric water content
c     thetar     - volumetric water content where hydraulic conductivity becomes zero
c     thetas     - saturated volumetric water content
c     ksat       - Saturated hydraulic conductivity (L/T) (modify to set units returned)
c     lambda     - Brooks adn Corey pore size interaction parameter 


c*** Local variable declarations ***
      real*4  satrat, minsatrat
      parameter( minsatrat = 1.0e-2 )
c     satrat     - conductivity relative saturation ratio
c     minsatrat  - used to clamp unsatcond_bc to zero and prevent underflow

      satrat = min(1.0,(theta-thetar)/(thetas-thetar))
      if( satrat.lt.minsatrat ) then
          unsatcond_bc = 0.0
      else
          unsatcond_bc = ksat*satrat**(2.5+2.0/lambda)
      endif
      return
      end