1. AGE 506 IRRIGATION ENGINEERING
Course Lecturer: Dr J.K. Adewumi
Dept. of Agricultural Engineering
UNAAB. Nigeria

2. Methods of Irrigation A. Surface Irrigation Sub- Irrigation
Wild flooding
Border strip
Check Basin
Furrow
Sub- Irrigation
Natural sub-irrigation (Advantages & disadvantages)
Artificial sub-irrigation (Advantages & disadvantages)
Overhead Irrigation
Rotating head systems
Perforated pipe system
Furrow irrigation
Border Irrigation
Level Border
Graded Border

3. Water Measurement in Open channel
Water measurement in pipes
Volume
Velocity
Orifices
Basin Flow Equations
Hydraulic Radius
Continuity Equation
Darcy-Weibach Equation
Bernoullis Equation

4. Measurement of Irrigation Water
Bucket and watch method
Float method
Flow from a vertical pipe
Flow from a horizontal pipe
Discharge from siphon tubes

5. 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
Methods of determining amount of irrigation
Tensiometer
C.U.
Available water moisture

6. 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

7. 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)

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. Class projects
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.