IRRIGATION engineering basics and description

IRRIGATION_2
Design of Irrigation Systems
by
László Ormos

Soil properties
Soil texture(water holding capacity)
• Clay <0.002 mm
• Silt 0.002-0.02mm
• Fine sand 0.02-0.2mm
• Coarse sand 0.2-2mm
• Gravel >2mm
percent sand
Soil texture
Sand
Loamy sand
Sandy loam Loam Silt loam Silt
Silty clay loam
Silty clay
Clay loam
Clay
Sandy clay

Soil properties
Soil structure (infiltration rate)
Single grains
Infiltration rate
rapid
(20-100mm/hr)
Platy
Infiltration rate
slow
(4-5mm/hr)
Prismatic
Infiltration rate
moderate

Soil-water-plant relationship
Soil moisture
Total water potential acting is as following:
where
Pt is the total water potential,
Pm is matric potential due to capillary forces,
• adhesion force (attractive force betweenthe solid particle and
the water)
• cohesion force (attraction between water molecules)
Pg is gravitational potential due to the gravity,
Po is osmotic potential due to the dissolved salts in the water,
Pp is pressure potential due to the position with respect to a fixed
datum level.
Pp
Po
Pg
Pm
Pt 




Classes and availabilities of soil water
Saturation
Field capacity
Permanent wilting
Gravitational water
Rapid drainage
Capillary water
Slow drainage
Hygroscopic water
Essentially no drainage
Available moisture
Unavailable moisture

Hysteresis effect
Moisture content
Suction

The movement of water in the soil
• Hydraulic conductivity (or flow velocity)
where
Q is the amount of water which moves through the soil,
A is the cross section area of the tested soil sample,
H is the difference in water pressure head between two points,
L is the distance between the two points,
KS is the Darcy coefficient of proportionality.
 
 
  K
cm
L
cm
H
cm
A
s
cm
Q
s
cm
V S















2
3

KS in saturated soil is the following:
KnS in unsaturated soil is the following:
where hG is the hydraulic gradient computed as follows:
H1 and H2 are pressure head values.
 
 
cm
H
cm
L
s
cm
V
KS 







 
hG
s
cm
V
H
KnS







   
 
cm
L
cm
H
cm
H
hG 1
2 


Infiltration under various methods of irrigation
• Furrow irrigation: gravitational influence,
• Flood irrigation: gravitational influence,
• Sprinkler irrigation: water distribution is more or less symmetrical,
• Micro-sprinkler: the distribution pattern is trapezoid, and wets the
area only partially (50-70%),
• Drip irrigation: cone-shaped volume of moistured soil surrounding the
plant root-zone, size and shape depend on the type
of soil, the discharge of dripper, and the duration of
water application.

Root
zone
extraction
Depth
D
40%
30%
20%
10%
D/4
D/4
D/4
D/4 10
3
0
20
30
40
Soil
depth
[cm]
7.4%
68.7%
10.3%
9.4%
4.2%
Water distribution in the soil Root distribution in the various
soil layers

Storage in soil
• Small pores are required to store the water.
• Medium-sized pores help the movement of water in the soil.
• Large-sized pores are required for aeration of soil.
The saturation
• Saturation capacity means the pores of soil are full filled with water.
• Gravity occurs the water drains quickly from the root zone.

Field capacity Fc
• The moisture content of soil means the remained water quantity after the
gravitational water has been removed.
• Field capacity depends on the texture of soil.
Permanent wilting point Pw
• It is the minimum of the available moisture of soil.
• When water content is at the wilting point or it is lower then plants
permanently wilt and they might not be recovered after being placed in
moisturized environment.
• Wilting point is influenced by soil texture.
Temporary wilting point
• It is occurred in any hot windy days but plants will recover in cooler portion
of days.

Available soil water AW
where AW is in percent of moisture volume, S is the specific density
of soil and W is the specific water density.
The depth of available soil water for a 1m layer AWDm
     
 















cm
g
cm
g
P
F
AW
W
S
W
C
3
3
%
%
%


     
  10
%
%
10
%
3
3
























cm
g
cm
g
P
F
AW
m
mm
AWDm
W
S
W
C



The depth of available water in the soil layer of depth Z AWDZ
where Z means the soil layer of depth.
The available water volume in the soil layer of depth Z AWVZ
 
 
m
Z
m
mm
AWDm
m
Z
mm
AWDZ 













   
10
3














 m
Z
mm
AWDZ
m
Z
ha
m
AWVZ

The depth of available water in the main root zone Zr of the
crop AWDZr
where Zr is the depth of main root zone.
After replacement in this equation, calculation directly the
depth of available water in the main root zone is as follows:
 
 
m
Zr
m
mm
AWDm
m
Z
mm
AWDZr 













 
   
    10
%
%
3
3























m
Zr
cm
g
cm
g
P
F
m
Zr
mm
AWDZr
W
S
W
C



The available water volume in the main root zone Zr of the
crop in a hectare AWZr
The net water application NWA
where PWD is the permitted water deficit.
The available net water application in the main root zone Zr
of the crop in a hectare AWZr
   
10
3














 m
Zr
mm
AWDZr
m
Zr
ha
m
AWVZr
     
%
PWD
mm
AWDZr
mm
NWA 

 
  10
3









mm
NWA
m
Zr
ha
m
NWA

The gross water application GWA
where irr is the efficiency of irrigation.
The irrigation interval IrI
where CU may be either the consumptive use, or evapotranspiration.
   
irr
mm
NWA
mm
GWA 
   







day
mm
CU
mm
NWA
days
IrI

Calculate the available water volume per hectare in a soil
with a homogeneous profile according to the following data:
• Field capacity Fc=17[%]
• Wilting point Pw=7 [%]
• Soil density S=1.3[g/cm3]
• Water density W=1.0[g/cm3]
• Main root zone Zr=0.4[m]

1. Available water by volume:
2. The depth of available water for a 1m layer:
3. The depth of available water in the effective root zone Zr:
   


W
S
W
C P
F
v
AW 


%
  10
% 







AW
m
mm
AWDm
 
 
m
Zr
m
mm
AWDm
m
Zr
mm
AWDZr 













  [%]
13
1
3
.
1
[%]
7
[%]
17
3
3
















cm
g
cm
g
  








m
mm
130
10
%
13
   
mm
m
m
mm
52
4
.
0
130 









4. The available water in a hectare, in the effective root zone Zr:
 
  10
3









mm
AWDZr
m
Zr
ha
m
AWVZr   








ha
m
mm
3
520
10
52

Calculate the available water volume per hectare in a soil with different
texture layer according to the following data:
Layer Layer
Depth
Layer
thickness
Soil
texture
Fc Pw S
[cm] [m] [%w] [%w] [g/cm3]
1 0-20 0.2 Sandy-
loam
13 5 1.5
2 20-35 0.15 loam 20 8 1.4
3 35-65 0.30 Clay-
loam
27 13 1.4
4 65-110 0.45 clay 32 16 1.3

The applied equation is
 
   
    10
%
%
3
3























m
Zr
cm
g
cm
g
P
F
m
Zr
mm
AWDZr
W
S
W
C


Fc-Pw
[%]
S
[g/cm3]
Zr
[m]
AWDZr
[mm/layer]
13-5 1.5 0.2
20-8 1.4 0.15
27-13 1.4 0.3
32-16 1.3 0.1
AWDZr (Zr=0.75m)
24.0
25.2
58.8
20.8
128.8

References
Azenkot, A.(1998):”Design Irrigation System”. Ministry of Agricul-
ture Extension Service (Irrigation Field service), MASHAV Israel
Dr. Avidan, A.(1995):”Soil-Water-Plant Relationship”. Ministry of
Agriculture Extension Service (Irrigation Field service), CINADCO,
Ministry of Foreign Affairs, MASHAV, Israel
Sapir, E.-Dr. E. Yagev (1995):”Drip Irrigation”. Ministry of Agricul-
ture and Rural Development, CINADCO, Ministry of Foreign Affairs,
MASHAV, Israel
Sapir, E.-Dr. E. Yagev (2001):”Sprinkler Irrigation”. Ministry of -
culture and Rural Development, CINADCO,Ministry of Foreign
Affairs, MASHAV, Israel
Eng. Nathan, R. (2002):”Fertilization Combined with Irrigation
(Fertigation)”. Ministry of Agriculture and Rural Development,
CINADCO,Ministry of Foreign Affairs, MASHAV, Israel

IRRIGATION engineering basics and description

More Related Content

Similar to IRRIGATION engineering basics and description (20)

More from sudheerchekka1 (7)

Recently uploaded (20)

IRRIGATION engineering basics and description