c     file name: aggss.for

      subroutine aggss ( ak, bseagg, semin, semax )

c     + + + PURPOSE + + +
c calculates agg stability increase due to pressure and wet dry cycle.
c eq. S(58), S(59)

c     + + + AUTHOR + + +
c     Imam Elminyawi

c     + + + KEY WORDS + + +
c     wind erosion, soil processes, aggregate stability

c     + + + ARGUMENT DECLARATIONS + + +
      real ak, bseagg, semin, semax

c     + + + LOCAL VARIABLES + + +
      real anc

c     + + + LOCAL DEFINITIONS + + +
c     anc

c     + + + END SPECIFICATIONS + + +

      anc = 0.0
      if ( bseagg .ge. semax .or. bseagg .le. semin) go to 100
         anc = -ak * alog(( semax - bseagg ) / ( semax - semin )) +1.0
         bseagg = (semax - semin) * ( 1.0 - exp(-anc / ak) ) + semin
 100  continue

      return
      end