ASFA Coverage Check
Choose a sprinkler and a spacing, and see how evenly the grid waters the ground: the average rate, CU, DU and the scheduling coefficient, with a map of where the water lands.
- Average rate
- 11.0 mm/h
- CU
- 96 %
- DU (low quarter)
- 95 %
- SC
- 1.05
- An hour of watering puts down 11.0 mm on average, from 10.2 mm at the driest point to 12.3 mm at the wettest.
- The heads stand 50 % of their throw diameter apart along a row. Head to head is 50 %.
- To give the driest 5 % of the ground the full depth, the system must run 1.05 times as long as the average needs.
5.5 mm/h or lessAverage
11.0 mm/hWetter
16.5 mm/h or more
A theoretical check. Each sprinkler here spreads its water in a typical shape, not the measured pattern of any product, and the grid is the middle of a large area in still air. Real systems usually score lower. The section below lists what is left out.
- Average rate (mm/h)
- The depth of water an hour of watering puts on the ground: the flow of one head divided by the area it serves (spacing × row spacing). Compare it with how fast your soil takes water in: a rate above it runs off.
- CU, Christiansen's coefficient of uniformity
- How close each point is to the average, as a percentage. 100 % would be perfectly even. It is worked out from the average difference between each point and the mean.
- DU, distribution uniformity of the low quarter
- The average of the driest quarter of the ground, as a percentage of the overall average. It looks only at the dry side, so it falls faster than CU when part of the lawn is short of water.
- SC, scheduling coefficient
- The average rate divided by the rate on the driest patch covering 5 % of the ground. It says how much longer the system must run so that the driest patch still gets the depth it needs. 1.0 would be perfectly even.
- Spacing, % of the throw diameter
- Head to head (each head reaching the next) is 50 %. The further past it, the more the ground between heads depends on a single head's outer throw, where it puts down least.
For comparison, the USDA NRCS standard for sprinkler systems (Conservation Practice Standard 442) asks for a CU of at least 85 % and a DU of at least 76 % where roots are shallow, as in lawns and most planting. Read the standard ↗
- The sprinkler's real pattern. Every head is given a typical shape. A real nozzle's pattern changes with its model, pressure and riser height, and only a catch-can test measures it.
- Wind. The air is still. Wind pulls the pattern downwind and shortens the throw upwind.
- The edges of the area. The grid goes on in every direction. Along a lawn's edge, part-circle heads and the missing neighbours change the result.
- Pressure and levels. Every head gets the same pressure and the ground is level, so every head throws the same water the same distance.
- Soil and plants. The figures are for water reaching the surface, not for how the soil spreads it or what the plants need.
A landscape design works from the chosen product's published data, the site's water supply and the shape of every area. See how ASFA designs landscape irrigation.
your project.
Send the location, the area, the type of site and the water source. We call you to talk it through and, if the project needs it, arrange a site visit.