CONCEPTUAL MODEL AND MODEL GRID
A loamy sand tillage plot typically in arid regions of northwest China
is considered for the present study. The irrigation rate from each
nozzle is assumed to be 6.94×10-4kg/s·m2 for the base case (C0; cf. Table 1) and the
infiltration presumably occurs with the same rate, given that the soil
is mostly dry in arid environment. The irrigation is delivered using a
sprinkling irrigation system, with the nozzles having spraying radius of
0.1 m and horizontal spacing of 0.3 m. The irrigation water is assumed
to be uniformly applied to the surface of the entire circular area.
Although there is supposed to be 38 nozzles in a length of 11.2 m in
reality, only 3 nozzles are considered in the model domain for
simplicity, as illustrated in Fig. 1. The VWCs for each depth interval
of 0.1 m inside the block of interest (BOI) are calculated for analysis
based on the numerical simulations.
The numerical code TOUGH2/EOS3 was chosen to simulate the processes of
soil imbibitions under infiltration induced by irrigation, as well as of
water redistribution due to drainage in the irrigation intermittence.
The lateral range and the depth of the model geometry are 11.2 m and 2.1
m, respectively (Fig. 1). The grid size ranges in horizontal from 0.1 m
close to the nozzle gradually up to 0.4 m at the periphery. The grid
refining interval is roughly between 480 and 660 cm of the X coordinate,
particularly in the vicinity of 0.3 m of the nozzles. The resulting mesh
has 800 elements and 2170 connections.
Since TOUGH2/EOS3 uses phase saturation as output, liquid saturation,
approximately equal to water saturation Sw , is
converted in some cases to VWC using the following formulation:
VWC = Sw ·ϕ (4)
The intrinsic permeability required for the current simulator is
calculated with the following formulation, since only the measurement of
saturated hydraulic conductivity ks is available
in the previous studies (Wang, 2013; Li, 2014).
\(K_{h}=\frac{\mu k_{s}}{\text{ρg}}\) (5)
Here, Kh denotes horizontal intrinsic
permeability [m2], μ is dynamic viscosity
[Pa·s], and the others are found in the above text.
Figure1. Grid design of the model.