Agriculture Reference
In-Depth Information
Fig. 3.3
Water flow pattern
in basin during inflow and
advance
Water front
Basin
Supply
channel
Check bank
3.3.3 Simulation Modeling for Basin Design
There are many design parameters which influence hydraulic processes during an
irrigation event in basin layouts. It is very difficult to predict and compare the per-
formance of alternative design layouts without using a physically based simulation
model to describe the process.
Generally, simulation models for basin irrigation design are based on governing
equations in the form of full hydrodynamic Saint-Venant equations or the simplified
zero-inertia approximation (neglecting inertial terms).
3.3.3.1 Hydrodynamic Model
In this approach, the overland flow is described by the depth-averaged hydrody-
namic flow equations. These equations consist of the continuity equation and the
momentum equation. The two-dimensional continuity equation for shallow water
∂
h
∂
t
+
∂
(
hu
)
∂
+
∂
(
hv
)
∂
+
I
s
=
0
(3.6)
x
y
where
u
and
v
are the velocities in
x
- and
y
-directions (m/s),
h
the water depth (m),
I
s
the volumetric rate of infiltration per unit area (m/s) and
t
is the time (s). The
momentum equations in the
x
- and
y-
directions are as follows:
(
u
2
h
)
∂
∂
(
uh
)
∂
+
∂
+
∂
(
uvh
)
∂
gh
∂
H
∂
+
x
+
ghS
f
x
=
0
(3.7)
t
x
y
(
v
2
h
)
∂
∂
(
vh
)
∂
+
∂
(
uvh
)
∂
+
∂
gh
∂
H
∂
+
y
+
ghS
f
y
=
0
(3.8)
t
x
y
where
g
is the acceleration due to gravity (m/s
2
),
H
h+
z
0
the water surface
elevation above the datum, z
0
the bottom elevation above an arbitrary datum (m),
and
S
fx
and
S
fy
are the components of friction slope in
x
- and
y
-directions. The first
=
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