C ***************************************************************

      real function availwc (
     m                       theta,
     i                       thetaw,
     i                       thetaf)

c     + + + PURPOSE + + +

c     availwc - Available water content ratio (mm/mm)
c     returns a linear function from thetaw=0 to thetaf=1

c     + + + ARGUMENT DECLARATIONS + + +

      real theta, thetaw, thetaf

c     + + + ARGUMENT DEFINITIONS + + +

c     theta  - actual water content (mm/mm)
c     thetaw - water content at wilting point (mm/mm)
c     thetaf - water content at field capacity (mm/mm)

c     + + + END SPECIFICATIONS + + +

      if (theta .lt. thetaw) then   ! can't be negative value
         availwc = 0.0
      else
         availwc = (theta - thetaw) / (thetaf - thetaw)
      endif
      if (theta .gt. thetaf) then     ! can't be greater than 1
         availwc = 1.0
      endif

      end