SAI
SAI in
E
SAI out
P
F
Figure 19. SA_I and SA_II. SAI, SA_I_in, SA_I_out, F,
SAII
and E are used to calculate the available storage in the
top soil layer (TP_LYR). SA_II, SA_I_in, SA_II_out, P,
and E are used to calculate the available storage in the
bottom soil layer (BTM_LYR).
SAII in
SAII out
where SA_I_in
=
E
(29)
SA_I_out
=
F
(30)
SA_II_in
=
P
(31)
SA_II_out
=
E.
(32)
The following equations are used to calculate F, E, and P:
F = FP_2
(33)
where
If
(RI_2 <=FP and STOR=0)
then
FP_2 = RI_2
If
(RI_2 > FP or STOR > 0)
then
FP_2 = FP
If
(SA_I = 0 and E < FP)
then
FP_2 = E .
(34)
Equations 25, 35 and 36 are used to calculate RI_2, FP and E respectively. Equation 35 represents the
Green Ampt Equation (Mein and Larsen 1973, Haan et al. 1982):
FP = KEFFa (1 + SAVa MDI/TINF)
(35)
Equations 36 and 37 calculate E and P respectively and are further described in Holtan et al. (1975):
SA_I G_I
E = [CSa (1 SAI/G_I)]
If
then
SA_I > = G_I
If
then
E=0
If
SA_II = 0
then
E=P
(36)
SA_II < G_II
P = [Du (1 SA_II/G_II)]
If
then
SA_II > = G_II
If
then
P = 0.
(37)
Demonstration of conservation of mass
Table 10 shows that mass is conserved in STOR because STOR minus F, minus STOR_EVAP,
plus RI_2, minus SURF for any hour equals the value of STOR in the following hour. Hours 4050
were selected for this table as F, RI_2, and SURF are equal to zero before 40 hours.
Table 11 shows that mass is conserved within TP_LYR because TP_LYR plus F, minus E, minus
TP_LYR_EVAP for any hour equal the value of TP_LYR for the following hour.
Table 12 shows that mass is conserved within BTM_LYR, because BTM_LYR plus E, minus P,
and minus BTM_LYR_EVAP for any hour equal the value of BTM_LYR for the following hour.
29
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