1. Introduction to Overhead/Sprinkler Irrigation Design
N.L Mufute ,
LWRM, MSU /

2. Introduction
Sprinkler Irrigation systems are systems which usually operate as pressurized piped systems delivering water to the crop by means of sprinklers.
Sprinkler irrigation is suited for most crops
Sprinkler systems can have unique uses such as seeding germination, Frost protection and fertigation.

3. Factors to consider when selecting Sprinkler Systems
Slopes,- : Sprinkler irrigation is adaptable to any farmable slope,(uniform or undulating).
Soils,- : Sprinklers are best suited to sandy soils with high infiltration rates although they are adaptable to most soils.
Water,- : Clean supply of water, free of suspended sediments/heavy metals, is required to avoid problems of sprinkler nozzle blockage and corrosion.

4. Advantages/Disadvantages of sprinkler irrigation
High suitability to various slopes
Micro-climate modification
Low labor input (comparable to surface)
Easily automated
High uniformity (compared to surface irrigation)
DISADVANTAGES
High initial cost (compared to surface irrigation)
High operation cost (e.g due to pumping)
Not suitable for some crops (e.g those do not require repeated wetting of leaves or with flowers that can be dislodged )
Canopy interception
Wind effect is considerable

5. Types of Sprinkler Systems
Permanent (Solid-set) system
Semi-portable (Hand-moved) system
Portable (Movable) system
Side-roll system
Center pivot system
Linear move system
Big gun /rain gun system

6. Components of a sprinkler system

7. DESIGN PROCEDURE: HAND MOVE SYSTEMS.
The procedure for designing sprinkler systems can be divided into two phases:
Preliminary design steps
Adjustment or final design steps
Preliminary design steps comprise the procedure for synthesizing farm data in order to determine preliminary design parameters, which will be needed in the final design adjustment process.
The final design steps reconcile the preliminary design parameters obtained with the irrigation equipment performance characteristics, as well as human, physical and financial factors.

8. Design Procedure for periodic-move sprinkler systems. Source: FAO, 2002

9. Steps in Sprinkler Irrigation Design
Step 1: Collect basic resource data at farm
The data include:
A topographic map showing:
The proposed irrigated area, with contour lines
Farm and field boundaries and water source or sources
Power points, such as electricity lines, in relation to water source and area to be irrigated, roads and other relevant general features such as obstacles
Data on water resources, quantity and quality over time, on water rights and on cost of water where applicable
The climate of the area and its influence on the water requirements of the selected crops
The soil characteristics and their compatibility with the crops and irrigation system proposed
The types of crops intended to be grown and their compatibility with both the climate in the area, the water availability and the soils; current agricultural practices should be identified

10. Steps in Sprinkler Irrigation Design
Step 2 : Analyze the farm data in order to determine the following preliminary design parameters:
peak and total irrigation water requirements
infiltration rate of soils to be irrigated
maximum net depth of water application per irrigation
irrigation frequency and cycle
gross depth of water application
preliminary system capacity
To achieve this designer will;
Determine moisture extraction depths (root zone depths=RZD)
Calculate Peak Water consumption use (Etc)
Define allowable depletion (P)
Calculate net irrigation application (dnet)
Calculate gross depth of application (dgr)
Calculate the irrigation frequency and cycle
Calculate preliminary system capacity (Q)

11. The final design process
Involve:
identification of irrigation system options with farmer participation
preparation of system layout for the field shape and topography
the hydraulic design and iterative adjustments
irrigation equipment selection taking into consideration economic and financial aspects
final irrigation system selection as well as options, taking into consideration farmers' preferences, management capabilities, labour aspects, financial capabilities and constraints
The final design process is intended to make the irrigation system selected compatible with the preliminary design factors.
Varies between the periodic-move systems and the continuous-move systems.
Also vary among the different types of sprinkler systems mentioned in the introductory section of this module.

12. Steps in Sprinkler Irrigation Design: Final Design Steps
To get to the final design, the designer will carry out the following steps;
Step 3; Sprinkler selection and spacing
Step 4; Determine Hydrant spacing
Step 5;Size Laterals and header lines.
Step 6 Sub main and Main line design/ sizing
Step 7 Size Delivery/supply line
Step 8 Determine the Total Dynamic Head (TDH)
Step 9 Determine the power requirements
Step 10 Select pump and power source
Step 11 Select other components and fittings
Step 12 Prepare Drawings and Map of Design
Step 13 Make a list of materials (Bill of quantities)
Step 14 Estimate the capital cost
Note: Several design options should be prepared and the final option should be chosen with the participation of the farmer / client;
Step 15 Choose final option.
Step 16 Prepare operation instructions

13. Exercise on Design
Given a surveyed piece of land (18ha) Fig 1, Design a suitable commercial semi portable system:
The following soil and crop data are provided;
Soil medium texture loam
Crop Wheat peak daily use 5.8mm/day
Available moisture 140mm/m and Allowable depletion (P)=50% or 0.5
RZD=0.7
Soil Infiltration rate 6mm/hr: Calc net depth of application
i.e.;
Determine the gross depth for the system operating at 85% efficiency
Calculate Irrigation frequency
Calculate the set time
Calculate the preliminary system capacity
Select appropriate sprinklers for the given conditions
Complete the design , layout and produce a Bill of Quantities.

14. Figure 1 : Farm map