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When designing the layout of an irrigation system, no matter the size of the project, the following fundamentals will always apply: pressure, head-to-head and zoning. Once these are taken into account, the chances of installing a system that results in high levels of efficiency are dramatically increased.
The rate of precipitation (ROP) of a sprinkler is the amount of water it distributes over a given area and amount of time. It is most commonly expressed in millimetres per hour (mm/hr). We use the ROP to calculate how long to run our irrigation zones in order to apply a specific amount of water to our garden. For example, if our ROP is 20 mm/h and we need to apply 10mm to our garden we would run the system for 30 minutes. Most manufacturers will provide an operating specifications sheet which will give you the ROP of a sprinkler under certain installation conditions. In some cases you may need to calculate the ROP, especially when your design doesn’t fit the exact criteria in the operating specifications sheet. In this article we will discuss how to calculate ROP from first principles.
In order to get maximum uniformity, sprinklers should be spaced at their radius. We call this head to head spacing. Viewed from above, this creates a grid-like pattern in our irrigation design with sprinklers spaced head to head both horizontally and vertically. The example below assumes a set of sprinklers with a 3m radius designed for a rectangular shaped section of garden 12 metres by 6 metres