Christiansen Uniformity Calculator

Calculator Inputs

Enter catch-can depths (or volumes) from a sprinkler test. You can paste values, upload a CSV, or use both for large grids.

Formula Used

The Christiansen Uniformity Coefficient (CU) measures how evenly water is applied across the test area:

• xi = each catch-can reading
• x̄ = average of all readings
• n = number of readings

This tool also reports DU (low quarter) as an extra uniformity indicator.

How to Use

1. Place catch-cans evenly across the irrigated area.
2. Run the system at normal pressure and runtime.
3. Measure collected depth in each can consistently.
4. Paste values or upload a CSV of readings.
5. Press Calculate and review CU, DU, and variability.
6. Adjust heads, pressure, and spacing to improve results.

Why Uniformity Matters in Garden Irrigation

Uniform irrigation keeps roots active and reduces stress. When some areas receive less water, plants compensate with shallow rooting, higher salinity around roots, and uneven canopy development. A higher CU supports consistent moisture, steadier nutrient uptake, and fewer “dry spots” that force longer runtimes. It improves fertilizer efficiency and plant color.

Design and Operating Factors That Change CU

Uniformity is influenced by nozzle selection, spacing, matched precipitation rates, pressure variation, elevation change, wind, and partially clogged screens. Pressure losses across valves and laterals can shift flow noticeably, especially on long runs. Check pressure at representative heads and compare it to the manufacturer’s recommended range.

Collecting Reliable Catch-Can Data

Place identical catch-cans on a regular grid covering the irrigated footprint. Keep cans level and above mulch splash. Use enough points to capture overlap patterns; 16–25 readings often provide stable statistics for small garden zones, while larger areas may need 30+. Run the system at normal schedule settings, then record depths promptly to reduce evaporation bias. If wind is present, repeat the test or average multiple runs.

Interpreting CU, DU, and Variability

CU is calculated from the average absolute deviation from the mean depth, so outliers strongly affect the score. DU (low quarter) focuses on the driest quarter and is useful for scheduling because plants suffer where application is lowest. As a practical guide, CU values around 80–90% indicate very good distribution for landscapes; 70–80% suggests improvement is worthwhile; below 70% often signals a mechanical or layout issue. Pair CU with CV: a lower CV indicates steadier performance across the zone.

Using Results to Improve Performance

If CU is low, begin with simple maintenance: clean filters, flush laterals, remove debris from nozzles, and replace worn parts. Confirm head-to-head spacing and correct mismatched arcs. Solve pressure problems with regulators, pressure-compensating heads, or zoning changes. After adjustments, re-test and store CSV/PDF results to track improvement over seasons and document service history for future tuning.

FAQs

What CU value is considered good for gardens?

Many landscape systems perform well around 80–90% CU. Values from 70–80% usually indicate you can improve nozzle selection, pressure, or spacing. Below 70% often points to clogging, misalignment, wind exposure, or significant pressure variation.

How many catch-cans should I place?

For small zones, 16–25 evenly spaced cans often capture overlap patterns. For larger or irregular areas, use 30 or more points. More samples reduce the impact of one unusual reading and make CU more reliable.

Can I enter collected volume instead of depth?

Yes, as long as all containers are identical and readings are comparable. Depth is common because it normalizes container area, but volume works if every can has the same opening size. Keep units consistent within one test.

Why does the calculator also show DU (low quarter)?

DU focuses on the driest quarter of the area, which typically controls plant stress and scheduling decisions. Two systems can have similar CU, yet different DU if one has a small dry region. DU helps prioritize fixes for weak spots.

What should I do if a reading is zero or negative?

Zero usually means the can was outside the wetted pattern, blocked, or tipped over. Reposition and repeat the test. Negative values are not physically meaningful and should be corrected at the source. This calculator requires positive readings.

How often should I retest uniformity?

Test after new installations, nozzle replacements, or pressure changes. For established systems, an annual check—plus a mid-season check in dusty or hard-water conditions—helps catch clogging early and keeps run times from creeping upward.