Identifying Soil and Transport Properties Using a Model
21
_{r/K, r y -
1
r ~ K,'
(5)
where r is the rate of effective water application determined as r= W/ta. Here W is
the volume of water infiltrating per unit soil surface area and ta is the duration of
water application, whereas the infiltration time ti =W/(yKs). When water is applied
at a rate less than the maximum infiltration rate of the soil, y < 1 and ti=ta• When
water is applied at a rate greater than the maximum infiltration rate of the soil, r=l
and ti>ta, representing ponding and no run-off. The front moisture content it, the
location of the water front Zj, and the specific discharge at the front location qj are
(6)
Redistribution occurs for t>ti. Solution of Eqs. (1) and (2) subject to the initial
condition 6(z. ti)=Br+(B,-Br )H[Zj(ti )-z] with ft and Zj(tJ defined by Eq. (6) and a
no-flux boundary condition q(O,t)=O (t>ti ) at soil surface is obtained as follows:
Bf(t)=Br+(Bs-Br)[~ f3]P
t ti + f3-1
(7)
The dependence of the wetted front coordinate zj. [Eqs. (6) and (7)] on time t is
shown in Fig. 2.
20
15
Z/W
10
5
- - - -
--Zc/ W
Zr/W: KdPb= 0.1
------- ------------------_.
Zr/W: KdPb= 0.5
---o~----------------------v---- o
10
20
30
40
50
tr/W
Fig. 2. The location of the front over time for water and solute (conservative and reactive).
In all cases Or=0.05, ~=0.35,Kir=3, jJ=1/3