AGE 506 IRRIGATION
ENGINEERING
Course Lecturer: Dr J.K. Adewumi
Dept. of Agricultural Engineering
UNAAB. Nigeria
Office Location: Postgraduate Building
Email: jkadewumi@yahoo.com
Course Outline
 Irrigation principles.
 Land preparation and farming for irrigation.
 Surface, sprinkler, trickle, and sub-surface irrigation systems.
Design of irrigation systems
 hydrologic design of small dams.
 Pumps
 hydraulic characteristic and selection for varying duties.
 Irrigation scheduling.
 Salt problems in irrigated agriculture,
 leaching and reclamation of saline and alkaline soils.
Course Requirement
 A compulsory course for all student in the
Department of Agriculture Engineering .
Students are expected to participate in all
the course activities and have minimum
of 75% attendance to be able to write the
final examination.
 They should also participate fully in all
practicals.
Reading list
 Principles of Irrigation Engineering by
Methods of Irrigation
A.
Surface Irrigation




Wild flooding
Border strip
Check Basin
Furrow
B.
Sub- Irrigation


Natural sub-irrigation (Advantages & disadvantages)
Artificial sub-irrigation (Advantages & disadvantages)
C.
Overhead Irrigation



Rotating head systems
Perforated pipe system
Furrow irrigation
D.
Border Irrigation


Level Border
Graded Border
Water Measurement in Open
channel
 Water measurement in pipes
 Volume
 Velocity
 Orifices
Basin Flow Equations
A
R
Hydraulic Radius
P
Continuity Equation
A1V1  A2V2  Q
 Darcy-Weibach Equation
 Bernoullis Equation
2
hL 
flv 2
2 gd
2
V1
P
V
P
 1  Y1  2  2  Y1  h
2g W
2g W
Measurement of Irrigation Water





Bucket and watch method
Float method
Flow from a vertical pipe
Flow from a horizontal pipe
Discharge from siphon tubes
Frequency and Amount of Irrigation

Methods of Frequency
•
Meteorological Method for determining CU or ETp for the plant
Blaney Criddle method
Plant Index method
(i) Crop itself
(ii) indicator Plant
(iii) change in leave colour
(iv) Physiological Index
Soil Index method
(i) Moisture content
(ii) Soil potential by tensiometer
•
•

(1)
(2)
(3)
Methods of determining amount of irrigation
Tensiometer
C.U.
Available water moisture
Irrigation Efficiencies

Reservoir Storage Efficiency
 Er = Ws/Wso X 100%,
Ws = amount of water directed, Wso = amount of water stored

Water conveyance Efficiency

Ec= Wf/Wr X 100%, Wf = amount of water delivered into farm, Wr = water diverted from reservoir

Water application Efficiency

Ea = Wst/Wf X 100% Where Wst = water stored in root zone ,

Overall Irrigation Efficiency

Ei = Er X Ec X Ea (100%) or Ei = Er/Wd where Wd = water stored or diverted for irrigation

Water distribution Efficiency

Ed = 1 – y where d = ave. depth of water stored along run during irrigation, y= ave. numerical deviation from d
d
Design of Sprinkler system
The following should be considered for design:
 Area of land
 Consumptive use of crop
 Water holding capacity
 Root zone depth
 Effective rainfall
 Water application efficiency
 Antecedent moisture content
 Net irrigation requirement
 Gross irrigation requirement
 Irrigation frequency
 Maximum time needed to apply dg (hrs)
Quality of irrigation water




Depends on amount and kind of salt present
Total salt concentration
Relative proportion
Bicarbonate and boron contents
Suitability of irrigation water can be expressed as SIW = f(QSPCD)
Where Q= quality of irrigation water
S = soil type
P = salt tolerance characteristics of the plant
C = climate
D= drainage characteristics of the soil
Drainage of Agricultural land
Effects of poor drainage on plants and soil
 Reduces aeration in soil
 Water-logging
 Anaerobic decomposition
 Temperature fluctuation in soil
Factors affecting rate of flow into drains
 Soil permeability
 Depth of soil
 Drain spacing
 Drain opening
 Drain diameter
 Distribution of potential at a flow boundary
Factors affecting erosion by water
Climatic factors
Soil characteristics
Topography
Vegetation
Phases of erosion
Detachment
Transportation
Deposition
Types of soil movement by wind
Suspension
Saltation
Surface creep
Gully Erosion
Aim of Gully Erosion Control
To reduce peak flow rate
To provide stable channel
Runoff reduction
Vegetative control
Structures
Stages of Gully Development
Channel erosion by downward scour of topsoil
Upstream movement of gully head
Healing stage
Stabilization of gully
Terraces
Terracing: An erosion control method
Types are:
Bench terrace
Broad based terrace
Functions of terraces
To decrease length of hill-side slope
To remove or retain runoff rate in area of inadequate rainfall
Terrace Design involves:

Proper spacing

Location of terraces

Design of channel with suitable capacity

Development of farmable cross-section
Terrace Spacing Location

Land slope

Soil condition

Proposed land use

Farm roads

Fences and outlet
Drainage and Reclamation
Process and practice involved in bringing saline and alkali soils into productive condition
Essentials of reclamation procedures:
Determine nature of the soil
Degree of salinity or alkalinity
Drainage Characteristics
Topography of the land
Presence of hardpan
Reclamation Procedure
Permanent reclamation
Lowering water table (if high)
Improving infiltration rate of soil
Leaching of salts in saline soils
Replacing excessive exchangeable Na by ca salts
Suitable management practice
Temporary reclamation
Removing the salts crust from surface of soil (Biological)
Ploughing salt surface-crust (Physical)
Neutralizing effects of salts (Chemical)
Synergic effects
Class projects
1.
2.
Design a channel of rectangular cross-section to carry water at the rate of 0.3m3/s a distance of 5 km if the
width is restricted to 1.5 m and the head loss along the length limited to 1 m. Consider lining to be of rough
concrete (n= 0.015)
Determine the system capacity for a sprinkler irrigation system to irrigate 16ha of maize crop. Design
moisture use rate is 5 mm/day. Moisture replaced in soil at each irrigation is 6 cm. Irrigation efficiency is
70%. Irrigation period is 10 days in a 12-day interval. The system is to be operated for 20 hours per day.