Irrigation Association Certified Irrigation
Designer Examination Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
Question 1
What is the primary purpose of the precipitation rate (PR) in sprinkler system
design?
A. To determine the total dynamic head of the pump
B. To calculate the system's friction loss in the mainline
C. To match the application rate to the soil's infiltration rate
D. To size the backflow prevention device
Answer: To match the application rate to the soil's infiltration rate
Rationale: The precipitation rate is the rate at which water is applied to the soil. If
the PR exceeds the soil's infiltration rate, runoff and erosion occur. Matching PR to
infiltration is fundamental to efficient irrigation design.**
Question 2
Which soil texture has the highest available water-holding capacity per foot of
depth?
A. Sand
B. Silt loam
C. Clay
D. Loamy sand
,Answer: Silt loam
Rationale: Silt loam typically holds about 1.8–2.0 inches of available water per
foot, higher than sand (≈0.5–0.7 in/ft) and clay (≈1.2–1.5 in/ft) due to optimal
pore size distribution. Loamy sand holds less than silt loam.**
Question 3
In a center pivot irrigation system, the end gun is used to:
A. Increase the wetted diameter at the outer end of the pivot
B. Reduce the operating pressure at the last tower
C. Flush the lateral line of debris
D. Measure the soil moisture content at the field edge
Answer: Increase the wetted diameter at the outer end of the pivot
Rationale: The end gun is a sprinkler mounted at the outermost span that extends
the wetted radius, covering corners or additional acreage that the pivot's regular
sprinklers cannot reach.**
Question 4
What does the term "head loss" refer to in a piping system?
A. The pressure gained by elevation increase
B. The energy lost due to friction and turbulence as water flows through pipes and
fittings
C. The vertical distance from pump to highest sprinkler
D. The flow rate reduction caused by a partially closed valve
Answer: The energy lost due to friction and turbulence as water flows through
pipes and fittings
Rationale: Head loss is the reduction in total hydraulic energy (pressure) caused by
friction between water and pipe walls, plus minor losses from fittings, valves, and
changes in direction.**
,Question 5
Which irrigation efficiency term is defined as the ratio of water beneficially used
to water applied, expressed as a percentage?
A. Distribution uniformity
B. Application efficiency
C. Scheduling efficiency
D. Conveyance efficiency
Answer: Application efficiency
Rationale: Application efficiency measures how much of the applied water is
stored in the root zone for crop use versus losses to deep percolation, runoff, or
evaporation. Distribution uniformity is a different measure of evenness.**
Question 6
For a drip irrigation system, the emitter flow rate is typically expressed in:
A. Gallons per minute (GPM)
B. Gallons per hour (GPH) or liters per hour (LPH)
C. Cubic feet per second (CFS)
D. Inches per hour (in/hr)
Answer: Gallons per hour (GPH) or liters per hour (LPH)
Rationale: Drip emitters discharge at very low rates, usually 0.5 to 4 GPH, so GPM
is too large a unit. Inches per hour applies to sprinkler precipitation rates, not
individual emitters.**
Question 7
What is the maximum recommended velocity in PVC irrigation pipelines to
prevent water hammer and excessive friction loss?
A. 1–2 ft/s
B. 3–4 ft/s
C. 5–7 ft/s
D. 10–12 ft/s
, Answer: 5–7 ft/s
Rationale: Industry standards (e.g., ASAE EP405) recommend velocities between 5
and 7 ft/s for PVC to limit friction losses and avoid water hammer damage. Higher
velocities increase surge pressures.**
Question 8
The Christiansen Coefficient of Uniformity (CU) is used to evaluate:
A. The chemical compatibility of fertilizers
B. The evenness of water distribution from a sprinkler system
C. The structural strength of irrigation pipe joints
D. The electrical conductivity of irrigation water
Answer: The evenness of water distribution from a sprinkler system
Rationale: CU is a statistical measure of how uniformly water is applied over an
area. It ranges from 0 to 100%, with higher values indicating more uniform
distribution.**
Question 9
What is the standard reference evapotranspiration (ET₀) grass surface used in the
Penman-Monteith equation?
A. Alfalfa at 40 cm height
B. Bermuda grass at 5 cm height
C. Tall fescue at 12 cm height
D. Kentucky bluegrass at 8–15 cm height
Answer: Tall fescue at 12 cm height
Rationale: The FAO-56 Penman-Monteith method defines ET₀ as a hypothetical
grass reference crop with a height of 0.12 m (12 cm), a fixed surface resistance of
70 s/m, and albedo of 0.23.**
Designer Examination Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
Question 1
What is the primary purpose of the precipitation rate (PR) in sprinkler system
design?
A. To determine the total dynamic head of the pump
B. To calculate the system's friction loss in the mainline
C. To match the application rate to the soil's infiltration rate
D. To size the backflow prevention device
Answer: To match the application rate to the soil's infiltration rate
Rationale: The precipitation rate is the rate at which water is applied to the soil. If
the PR exceeds the soil's infiltration rate, runoff and erosion occur. Matching PR to
infiltration is fundamental to efficient irrigation design.**
Question 2
Which soil texture has the highest available water-holding capacity per foot of
depth?
A. Sand
B. Silt loam
C. Clay
D. Loamy sand
,Answer: Silt loam
Rationale: Silt loam typically holds about 1.8–2.0 inches of available water per
foot, higher than sand (≈0.5–0.7 in/ft) and clay (≈1.2–1.5 in/ft) due to optimal
pore size distribution. Loamy sand holds less than silt loam.**
Question 3
In a center pivot irrigation system, the end gun is used to:
A. Increase the wetted diameter at the outer end of the pivot
B. Reduce the operating pressure at the last tower
C. Flush the lateral line of debris
D. Measure the soil moisture content at the field edge
Answer: Increase the wetted diameter at the outer end of the pivot
Rationale: The end gun is a sprinkler mounted at the outermost span that extends
the wetted radius, covering corners or additional acreage that the pivot's regular
sprinklers cannot reach.**
Question 4
What does the term "head loss" refer to in a piping system?
A. The pressure gained by elevation increase
B. The energy lost due to friction and turbulence as water flows through pipes and
fittings
C. The vertical distance from pump to highest sprinkler
D. The flow rate reduction caused by a partially closed valve
Answer: The energy lost due to friction and turbulence as water flows through
pipes and fittings
Rationale: Head loss is the reduction in total hydraulic energy (pressure) caused by
friction between water and pipe walls, plus minor losses from fittings, valves, and
changes in direction.**
,Question 5
Which irrigation efficiency term is defined as the ratio of water beneficially used
to water applied, expressed as a percentage?
A. Distribution uniformity
B. Application efficiency
C. Scheduling efficiency
D. Conveyance efficiency
Answer: Application efficiency
Rationale: Application efficiency measures how much of the applied water is
stored in the root zone for crop use versus losses to deep percolation, runoff, or
evaporation. Distribution uniformity is a different measure of evenness.**
Question 6
For a drip irrigation system, the emitter flow rate is typically expressed in:
A. Gallons per minute (GPM)
B. Gallons per hour (GPH) or liters per hour (LPH)
C. Cubic feet per second (CFS)
D. Inches per hour (in/hr)
Answer: Gallons per hour (GPH) or liters per hour (LPH)
Rationale: Drip emitters discharge at very low rates, usually 0.5 to 4 GPH, so GPM
is too large a unit. Inches per hour applies to sprinkler precipitation rates, not
individual emitters.**
Question 7
What is the maximum recommended velocity in PVC irrigation pipelines to
prevent water hammer and excessive friction loss?
A. 1–2 ft/s
B. 3–4 ft/s
C. 5–7 ft/s
D. 10–12 ft/s
, Answer: 5–7 ft/s
Rationale: Industry standards (e.g., ASAE EP405) recommend velocities between 5
and 7 ft/s for PVC to limit friction losses and avoid water hammer damage. Higher
velocities increase surge pressures.**
Question 8
The Christiansen Coefficient of Uniformity (CU) is used to evaluate:
A. The chemical compatibility of fertilizers
B. The evenness of water distribution from a sprinkler system
C. The structural strength of irrigation pipe joints
D. The electrical conductivity of irrigation water
Answer: The evenness of water distribution from a sprinkler system
Rationale: CU is a statistical measure of how uniformly water is applied over an
area. It ranges from 0 to 100%, with higher values indicating more uniform
distribution.**
Question 9
What is the standard reference evapotranspiration (ET₀) grass surface used in the
Penman-Monteith equation?
A. Alfalfa at 40 cm height
B. Bermuda grass at 5 cm height
C. Tall fescue at 12 cm height
D. Kentucky bluegrass at 8–15 cm height
Answer: Tall fescue at 12 cm height
Rationale: The FAO-56 Penman-Monteith method defines ET₀ as a hypothetical
grass reference crop with a height of 0.12 m (12 cm), a fixed surface resistance of
70 s/m, and albedo of 0.23.**
