Inputs
Example Data Table
Sample catch readings from one sprinkler zone, measured for 15 minutes.
| Can # | Depth (mm) | Notes |
|---|---|---|
| 1 | 12 | Near head, moderate spray |
| 2 | 14 | Overlap area, higher catch |
| 3 | 10 | Edge coverage, lighter pattern |
| 4 | 16 | Strong stream, possible mismatch |
| 5 | 13 | Center line, typical catch |
| 6 | 11 | Shaded corner, lower wind effect |
| Tip: aim for 8–16 cans for medium zones. | ||
Formula Used
- Average Catch Depth: Avg = (Σ readings) ÷ n
- Low Quarter Average: sort readings, take the lowest 25%, then average them.
- Distribution Uniformity: DUlq (%) = (LowQuarterAvg ÷ Avg) × 100
- Precipitation Rate: Rate (in/hr) = AvgDepth (in) ÷ Runtime (hr)
- Schedule Minutes (optional): Minutes/week = WeeklyNeed (in) ÷ Rate × 60
DUlq helps reveal dry spots. Use it to guide nozzle, pressure, and spacing adjustments before increasing runtime.
How to Use This Calculator
- Place identical catch cans evenly across one zone.
- Run the zone for a fixed time, like 10–20 minutes.
- Measure each can depth, then paste all values.
- Choose units, enter runtime, and calculate the audit.
- Improve uniformity first, then fine-tune the schedule.
Catch-Can Layout and Sample Size
Place 8–16 identical cans in a grid that matches sprinkler spacing. Keep each can level, and at least 30 cm from hard edges that cause splash. For rotor zones, use a wider grid because throw distance varies across the radius. Record the zone runtime. This layout keeps results comparable after repairs for accurate zone benchmarking.
Interpreting DUlq Scores for Turf and Beds
DUlq compares the lowest quarter of cans to the overall average. Values below 60% usually signal major coverage problems, such as clogged nozzles, broken heads, or pressure imbalance. A 70–80% range is common for well-tuned fixed spray zones. Above 80% often indicates strong overlap and stable pressure. Use DUlq to fix dry spots before adding minutes, otherwise wet areas become overwatered.
Precipitation Rate and Weekly Runtime Planning
Precipitation rate converts the average catch depth into inches per hour for the tested runtime. Combine the rate with a target weekly water depth to estimate minutes per week. If the calculated minutes per cycle are long, split watering into shorter cycles with soak time to limit runoff on slopes or compacted soils. After changing nozzles or pressure, re-run the test because precipitation rate can change significantly.
Efficiency Losses You Can Quantify
Large differences between cans raise the coefficient of variation and point to wasted water. Wind, mismatched arcs, and tilted heads reduce uniformity and push more water onto pavement. Low-quarter readings indicate what the driest areas receive, so scheduling to the low quarter protects plant health. Fix hardware first, then lower the weekly target gradually while monitoring plant response and soil moisture.
Re-Audit Frequency and Tracking Improvements
Audit each zone at least once per season and after any major maintenance. Store results as CSV and compare DUlq, precipitation rate, and low-quarter depth across dates. A 5–10 point DUlq improvement can allow shorter runtimes without sacrificing coverage. Keep notes on nozzle type, pressure adjustments, and head alignment so you can repeat the best setup next year.
FAQs
1) How many catch cans should I use?
Use 8–16 cans for most zones. Small bed zones can work with 6–8, while larger turf zones benefit from 16+ cans. More samples produce a steadier DUlq and precipitation rate.
2) What DUlq value is acceptable?
For many home systems, 70–80% is a strong target. Below 60% usually indicates faults worth fixing first. Above 80% suggests good overlap and stable pressure, though wind can still shift results.
3) Why is my precipitation rate unusually high?
High rates can come from short runtimes, small catch cans, or high-flow nozzles. It may also indicate mixed nozzle sizes or excessive pressure. Verify runtime timing, then check nozzle matching and pressure regulation.
4) Should I schedule to the low quarter or the average?
Schedule to protect the dry spots, but improve uniformity first. If DUlq is low, watering to the low quarter can overwater wet areas. After repairs raise DUlq, scheduling becomes more efficient and safer.
5) How do I choose target weekly water?
Start with local guidance for turf or your crop stage, then adjust using soil and plant cues. Enter that weekly depth here to estimate minutes per week. Reduce in small steps after uniformity improves.
6) When should I run the audit again?
Re-audit after nozzle changes, pressure adjustments, or repairs, and once per season for each zone. Comparing CSV results over time helps confirm that uniformity and runtime needs are actually improving.