Irrigation Systems Design and Installation

Design and Installation of Irrigation Systems

Chapter Introduction

This chapter covers all the knowledge required for the Red Seal exam in landscape horticulture regarding irrigation systems. You must master hydraulic principles, components, installation procedures, design calculations, and applicable Canadian standards. This chapter is structured to follow the logic of the complete process: from site analysis to commissioning, including sizing and installation.

Fundamental Hydraulic Principles

Pressure, Flow Rate, and Pressure Loss

Pressure is the force exerted by water on the walls of a conduit, measured in kilopascals (kPa) or pounds per square inch (psi). Static pressure is measured when water is at rest; dynamic pressure is measured under flow conditions. The difference between the two represents pressure losses (friction) in the system.

Flow rate (Q) is the volume of water flowing per unit of time, measured in litres per minute (L/min) or cubic metres per hour (m³/h). The fundamental relationship is:

Q = V × A

where V is velocity (m/s) and A is the cross-sectional area of the pipe (m²). In practice, flow tables are used for standard pipe diameters.

The recommended velocity in irrigation pipes is 0.6 to 1.5 m/s. Beyond 2.1 m/s, the risk of water hammer and internal erosion increases significantly.

Darcy-Weisbach Law and Hazen-Williams Formula

For pressure loss calculations in plastic pipes (PVC and polyethylene), the Hazen-Williams formula is used:

hf = 10.67 × L × Q^1.852 / (C^1.852 × D^4.871)

where:

hf = pressure loss (m)

L = pipe length (m)

Q = flow rate (m³/s)

C = roughness coefficient (150 for PVC, 140 for PE)

D = inside diameter (m)

In practice, designers use charts or calculators, but you must understand the impact of each variable: doubling the diameter reduces pressure loss by a factor of approximately 2^4.87 ≈ 29. This is why it is almost always better to increase the pipe diameter rather than increase the pressure.

Working Pressure and Pressure Rating

The pressure rating (PR) of a pipe is the maximum pressure it can withstand continuously at 20 °C. For PVC, common classes are PR 1380 kPa (200 psi) and PR 1035 kPa (150 psi). For polyethylene, ASTM D2239 or D3035 standards are often used. The actual working pressure must never exceed 75% of the pipe's pressure rating.

Site Analysis and Water Requirements

Assessing Available Pressure and Flow Rate

Before any design, you must measure the static pressure at the point of connection using a pressure gauge. Then, measure the available flow rate using the bucket-and-stopwatch method or a flow meter. The dynamic pressure at the required flow rate must be at least 280 kPa (40 psi) for a residential sprinkler irrigation system, and 350 kPa (50 psi) for commercial systems.

Calculating dynamic pressure: subtract from the static pressure the pressure losses of the water meter, existing piping, backflow preventer, and main valve. A rule of thumb: the water meter and municipal piping consume 35 to 70 kPa depending on flow rate.

Plant Water Requirements

A plant's water requirement is a function of evapotranspiration (ET), which combines soil evaporation and leaf transpiration. ET is expressed in millimetres per day (mm/day). In Canada, reference ET (ET₀) ranges from 3 to 7 mm/day during the growing season depending on the region.

The net irrigation water requirement is calculated:

Net requirement = ET₀ × Kc − Effective precipitation

where Kc is the crop coefficient (0.4 for mature trees, 0.6 for shrubs, 0.8 for lawns, 1.0 for annual flower beds).

Example: For a lawn in Toronto in July (ET₀ = 5 mm/day, Kc = 0.8, effective precipitation = 0), the net requirement is 4 mm/day. For an area of 500 m², the daily volume is:

V = 4 mm × 500 m² = 0.004 m × 500 m² = 2.0 m³ = 2000 L/day

Zoning and Hydrozones

Zoning involves grouping plants with similar water requirements onto separate valves (zones). Three main hydrozones are distinguished:

High zone: established trees and shrubs (low requirement)

Medium zone: ornamental shrubs, perennials

Low zone: lawns, annual flower beds (high requirement)

Never mix sprinklers and drip emitters on the same valve: their pressures and flow rates are incompatible.

Irrigation System Components

Pipes and Tubing

Type	Common Diameters	Use	Pressure Rating
Rigid PVC (Schedule 40)	13–50 mm (1/2–2 in)	Buried mainlines and laterals	1380 kPa
PVC (Schedule 80)	13–50 mm	Threaded fittings, pressure parts	2760 kPa
Polyethylene (PE)	13–32 mm	Laterals, drip systems	1035–1380 kPa
Low-density polyethylene (LDPE)	6–19 mm	Drip emission tubing	400–700 kPa

PVC is rigid, UV-resistant once buried, and joined by solvent cementing. Polyethylene is flexible, resistant to freezing (to a certain extent), and joined with compression or insert fittings. For buried systems in Canada, the minimum depth is 0.30 m below the frost line (typically 1.2 to 1.8 m depending on the region).

Valves and Solenoid Valves

Manual valves (ball or butterfly type) are used for isolating sections. Solenoid valves (electric valves) are controlled by the controller. Solenoid valves are normally closed (NC): they open when 24 V AC current is applied to the solenoid.

Solenoid valves are available in globe (angle) or diaphragm configurations. The nominal diameter ranges from 19 mm (3/4 in) to 50 mm (2 in). The pressure loss through a solenoid valve is typically 35 to 70 kPa at rated flow.

Sprinklers and Nozzles

Sprinklers fall into three categories:

Type	Throw Distance	Working Pressure	Precipitation Rate
Rotary (impact)	9–25 m	280–450 kPa	5–15 mm/h
Gear-driven rotors	6–15 m	280–480 kPa	10–20 mm/h
Spray (fixed)	2–5 m	200–280 kPa	25–50 mm/h

The precipitation rate (application rate) of a sprinkler is:

Precipitation (mm/h) = (Nozzle flow in L/min × 60) / (Spacing × Throw in m)

Example: A rotor with a 20 L/min nozzle, 12 m × 12 m spacing:

Precipitation = (20 × 60) / (12 × 12) = 1200 / 144 = 8.3 mm/h

Drip and Micro-Irrigation

Drip irrigation (localized irrigation) includes:

Drip emitters: flow rate of 2 to 8 L/h, working pressure 100–200 kPa

Emitter tubing (porous pipe): 2 to 4 L/h per metre

Micro-sprinklers: flow rate 20–120 L/h, throw distance 1–4 m

Drip irrigation requires filtration (disc or screen filter of 120 to 200 mesh) and a pressure regulator (reduces pressure to 150–200 kPa). A backflow preventer is mandatory to prevent water from returning into the potable water supply.

Controller (Timer)

The controller controls the opening and closing of solenoid valves according to a schedule. Modern controllers offer:

Programming by day of the week or by interval

Run time per zone (1–240 minutes)

Multiple start times (cycles) for soils with low infiltration rates

Rain sensor (mandatory in several Canadian municipalities)

Soil moisture sensor (optional)

Wi-Fi connectivity and remote control

The controller must be installed in an accessible location, protected from the weather, and powered by a 24 V AC transformer (Class 2). The transformer capacity must be sufficient for all simultaneously operating solenoid valves (each solenoid draws 0.3 to 0.5 A at start-up).

System Design

"Head-to-Head" Design Rule

Sprinkler spacing must ensure sufficient overlap for uniform distribution. The "head-to-head" rule requires that each sprinkler's throw reach the adjacent sprinkler. For windy conditions (common in the Prairies), reduce spacing to 50% of the throw.

Coefficient of Uniformity (CU): Christiansen's CU must be ≥ 75% for sprinkler systems, and ≥ 85% for drip irrigation. A low CU indicates water waste and dry spots.

Calculating the Number of Zones

The number of zones (valves) is calculated from the total available flow rate:

Number of zones = Total available flow rate (L/min) / Flow rate per zone (L/min)

Example: Available flow rate = 80 L/min. Each spray sprinkler zone consumes 40 L/min (8 heads × 5 L/min). Number of zones = 80 / 40 = 2 zones.

Sizing Pipes

The sizing of mainlines and laterals must respect the maximum velocity constraint of 1.5 m/s. Use the following table as a reference:

Nominal Diameter (in)	Inside Diameter (mm)	Max Flow at 1.5 m/s (L/min)
1/2	16	18
3/4	21	31
1	27	51
1 1/4	35	87
1 1/2	41	119
2	53	199

Slope and Drainage

On sloped terrain, install drain valves (automatic drains) at the low points of the system to empty the pipes before freezing. The slope of pipes must be at least 0.5% (5 mm per metre) toward drain points. For mainlines, install pressure relief valves if the static pressure exceeds 700 kPa.

Installation

PVC Pipe Installation Procedure

90.Trench: minimum depth of 0.30 m below the frost line; sufficient width to work (0.15 m on each side of the pipe).

91.Bedding: the pipe rests on compacted soil, free of sharp stones. A 50 mm sand bed is recommended in rocky soils.

92.Assembly: cut the pipe at a right angle, chamfer the end, apply primer (cleaner) then solvent cement to both surfaces. Insert with a quarter-turn rotation and hold for 15 seconds.

93.Cure time: respect the cement cure time (30 minutes to 1 hour before pressurizing, depending on temperature).

94.Pressure test: perform a test at 1.5 times the working pressure, maintained for 30 minutes, before backfilling.

Solenoid Valve Installation

Solenoid valves are installed in valve boxes accessible at ground level. Each box must be:

Sized to allow valve removal

Marked for identification (zone number)

Surrounded by drainage gravel (150 mm below and around)

Wiring for solenoid valves uses a common wire (usually white) and one individual wire per valve (different colours). Connections must be watertight (gel connectors or crimped connectors with heat-shrink tubing). The cable is laid in the same trench as the pipes, at least 150 mm above the pipe.

Connection to the Water Supply

The connection to the potable water supply must include:

103.A backflow preventer conforming to CSA B64 standard (backflow prevention device)

104.A shut-off valve (isolation) upstream of the backflow preventer

105.A drain cock downstream of the backflow preventer

The backflow preventer must be installed above ground, protected from freezing, or in a heated pit. In Canada, the reduced pressure (RP) type is required for high-hazard installations (chemical injection), while the double check (DC) type is sufficient for conventional sprinkler systems.

Electrical Connection

The controller must be powered by a dedicated 120 V AC circuit protected by a 15 A breaker. According to the Canadian Electrical Code, Part I (CE Code) (C22.1), Rule 8-200, conductors must be sized for the load and protected against overcurrent. The 24 V AC transformer must be installed at least 300 mm above the ground and protected from water spray.

Low-voltage wiring (24 V) must be:

Buried at least 150 mm in the ground

Protected by rigid conduit where it emerges from the ground

Identified with a "24 V irrigation" label

Commissioning and Adjustment

Flushing and System Testing

After installation, proceed as follows:

117.Flushing: open the main valve and let water flow through the open ends of the pipes for 5 minutes to remove debris.

118.Air purging: open the valves manually (without the controller) and let air escape through the sprinklers.

119.Leak check: inspect all connections during pressure build-up.

120.Nozzle adjustment: adjust the arc and throw of each sprinkler to avoid watering impervious surfaces (sidewalks, walls).

Controller Adjustment

The run time adjustment is calculated:

Run time (minutes) = (Net requirement in mm × 60) / Precipitation rate (mm/h)

Example: Net requirement = 4 mm/day, precipitation rate = 8.3 mm/h

Run time = (4 × 60) / 8.3 = 240 / 8.3 = 29 minutes

If the soil has low infiltration (clay), divide the run time into two cycles spaced at least 1 hour apart to avoid runoff.

Winterization (Winterizing)

In Canada, winterization is critical. Standard procedure:

129.Close the main valve and open the drain cock.

130.Gravity drainage: open all manual valves and automatic drains.

131.Compressed air blowout (recommended method): use a compressor providing 0.3 to 0.5 m³/min per zone. Air pressure must not exceed 500 kPa. Blow out each zone for 1 to 2 minutes until water is completely evacuated.

132.Protect the backflow preventer: drain it and insulate it with insulating material.

133.Remove the controller (if not designed for winter outdoor use) or cut the power supply.

Caution: never blow compressed air through the backflow preventer without bypassing it — you risk damaging it.

Applicable Standards and Codes

Canadian Electrical Code, Part I (CE Code) (C22.1)

Electrical installations for irrigation systems must comply with:

Rule 8-200: conductor sizing and overcurrent protection

Rule 12-1000: conductor installation methods (burial, conduits)

Rule 26-700: motor and control installations (if pumps are used)

CSA B64 — Backflow Prevention Devices

The CSA B64 standard governs backflow prevention devices for potable water installations. Key requirements:

B64.4: double check valve (DC) — for sprinkler systems

B64.4.1: reduced pressure (RP) — for systems with chemical injection

B64.10: installation and maintenance of backflow prevention devices

The device must be tested annually by a certified technician.

CSA B149.1 — Natural Gas and Propane Code

This standard applies only if your irrigation system uses a gas-powered engine (pump). Requirements cover ventilation, gas piping, and safety devices. In practice, electric pumps are almost always used for irrigation.

Other Relevant Standards

ASTM D1785: PVC pipes (Schedules 40 and 80)

ASTM D2239: polyethylene (PE) pipes

ASABE S398.1: test procedure for sprinklers

ISO 15886: irrigation sprinklers — requirements and test methods

Common Pitfalls to Avoid

157.Neglecting dynamic pressure: designing using static pressure leads to under-supplied sprinklers. Always calculate the dynamic pressure at the farthest point.

158.Mixing emitter types on the same zone: sprinklers and drip emitters have incompatible pressures and flow rates.

159.Underestimating fitting pressure losses: each elbow, tee, and valve adds a loss equivalent to 0.5 to 2 m of straight pipe.

160.Ignoring the frost line: a pipe installed too shallow will freeze and crack. Check the local frost depth (often 1.2 to 1.8 m in Canada).

161.Forgetting the backflow preventer: this is a legal (CSA B64) and health requirement. Its absence can contaminate the potable water supply.

162.Blowing compressed air too hard: air pressure above 500 kPa can blow apart fittings and damage solenoid valves.

163.Not testing uniformity: installing without checking the CU leads to dry or waterlogged areas. Use catch cups to validate distribution.

164.Programming without considering the soil: clay soil requires short, frequent cycles; sandy soil requires longer, less frequent cycles.

165.Using undersized pipes: velocity exceeds 1.5 m/s, causing noise, water hammer, and premature wear.

166.Not documenting the "as-built" plan: the as-built plan is essential for future maintenance and locating valves.

Summary

Dynamic pressure is the design value; static pressure serves only as a starting point.

Velocity in pipes must remain between 0.6 and 1.5 m/s.

Zoning (hydrozones) groups plants by similar water requirements.

The "head-to-head" rule ensures a minimum overlap of 100% of the throw.

A backflow preventer conforming to CSA B64 is mandatory for any connection to the potable water supply.

Winterization by compressed air blowout (max 500 kPa) is essential in Canada.

The Canadian Electrical Code, Part I (CE Code) governs electrical installation (Rules 8-200, 12-1000, 26-700).

Run time is calculated from the net water requirement and the system's precipitation rate.

The as-built plan must be provided to the client for future maintenance.

Self-Assessment Questions

180.A system has a static pressure of 550 kPa. Total pressure losses (meter, backflow preventer, pipes) are 120 kPa. What is the available dynamic pressure?

181.Calculate the precipitation rate of a rotor with a 30 L/min nozzle, 10 m × 10 m spacing.

182.An 800 m² lawn area requires 5 mm/day. The system has a precipitation rate of 12 mm/h. What is the daily run time?

183.Name the three types of sprinklers and their working pressure ranges.

184.What is the minimum burial depth for irrigation pipes in your region? (Refer to the local frost line.)

185.What are the two most relevant Canadian Electrical Code rules for installing an irrigation controller?

This chapter covers the essential knowledge for the Red Seal exam in landscape horticulture. For further study, consult the CSA B64 standards, the Canadian Electrical Code (C22.1), and the design guides from irrigation equipment manufacturers.