subroutine calchc(smst,poros,wilt,satk,usatk,fldcap)
c     subroutine calchc(hour,smst,poros,wilt,satk,usatk,
c    1                                   fldcap,adj,tillq)
c
c     +++PURPOSE+++
c     This function is called from the "init" function and its
c     purpose is to calculate the Hydraulic Conductivity of both
c     the unsaturated tilled and untilled unfrozen soil layers.
c
c     Authors(s):  John Witte, UofMn WCES @ USDA-ARS-NCSRL
c     Date: 10/27/93

c     Verified and tested by Reza Savabi, USDA-ARS, NSERL 317-494-5051
c                  August 1994
c
c     +++ARGUMENT DECLARATIONS+++
      real     smst,poros,wilt,satk,usatk,fldcap
c     real     smst,poros,wilt,satk,usatk,fldcap,adj
c     integer  hour,tillq
c
c     +++ARGUMENT DEFINITIONS+++
cc    hour   - Hour of the day.
c     smst   - Soil moisture of particular layer.  (%/100)
c     poros  - The porosity of the soil in decimal percent units.
c     wilt   - 1/3-bar water capacty..referred to as wilting pt(%/100)
c     usatk  - Unsaturated Hyd Conductivity for the soil. (m/hr)
c     satk   - Saturated Hyd Conductivity for the soil. (m/hr)
c     fldcap - Field capacity of the soil layer. (%/100)
cc    adj    - Adjustment factor.
cc    tillq  - Query to inform whether or not into untilled layer.
c
c     +++PARAMETERS+++
      include 'pmxpln.inc'
      include 'pmxnsl.inc'
      include 'pmxhil.inc'
      include 'pmxtls.inc'
      include 'pmxtil.inc'
      include 'pmxcrp.inc'
c
c     +++COMMON BLOCKS+++
      include  'cstruc.inc'
c       read:  iplane
      include  'cwater.inc'
c       read:  ssc,st,thetafc(mxnsl)
c
      include  'cwint.inc'
c       read:  thetdr,ssc,hk
c
c      include  'cparame.inc'
c       read:  ks

c     +++LOCAL VARIABLES+++
c
c XXX Use of the global SAVE does not follow the WEPP coding conventions
c     This needs to be fixed so that only the local variables which
c     need to have their values retained are saved.  dcf  5/18/94
      save
c     real     satn,avail,uplim,persat,corfac,fcap,tenscm
      real     tenscm, p, slo
c
c     +++LOCAL DEFINITIONS+++
c     satn   -
c     avail  -
c     uplim  -
c     persat -
c     corfac -
c     fcap   -
c     tenscm - Soil tension for the particular soil layer. (cm)

c
c     +++END SPECIFICATIONS+++
c
c
c

cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
c                                                                    c
c   Hydraulic Conductivity calculations for both tilled and untilled c
c   Unsaturated soil layers.                                         c
c                                                                    c
cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc


c -- Here, we are using all of the data that we can from the WEPP
c -- water balance in order to save us some run-time and some work.
c -- After the first hour, then we must take care of our own adjust-
c -- ments for the other 23 hours.


c     satn = smst / poros
c     avail = satn * (poros - wilt)
c     uplim = (poros - wilt)
c     persat = avail / uplim

c -- Here is where the other 23 hours come from...
c     if (hour .gt. 1) then
c       fcap = fldcap - wilt
c       adj = -2.655 / alog10(fcap/uplim)
c     endif

c     corfac = persat**adj
c     usatk = corfac * satk

c -- Currently, we have been using the method of Prasanta Kalita's for
c -- determining the value of unsaturated hydraulic conductivity based
c -- on soil tension in units of cm.

c -- tenscm = 50.0

      slo = 100.0 * (fldcap - wilt) / 1.518514
      p = 100.0 * (poros - smst) / abs(slo)
      tenscm = (10**p) * 10.0


      if (tenscm .le. 15.0) then
        usatk = satk
      endif

      if ((15.0 .lt. tenscm) .and. (tenscm .le. 41.0)) then
        usatk = satk * (10**(1.06 - 0.98 * alog10(tenscm)))
      endif

      if ((41.0 .lt. tenscm) .and. (tenscm .le. 450.0)) then
        usatk = satk * (10**(-131.3 + 265.0 * alog10(tenscm) -
     1                  199.4 * (alog10(tenscm)**2) +
     2                   66.2 * (alog10(tenscm)**3) -
     3                    8.2 * (alog10(tenscm)**4)))
      endif

      if (tenscm .gt. 450.0) then
        usatk = satk * (10**(-12.1 + 7.58 * alog10(tenscm) -
     1                             1.63 * (alog10(tenscm)**2)))
      endif

      return
      end