IRRIGATION: IRRIGATION – GOOD DESIGN

Good sprinkler systems should water the area completely, uniformly, and in accordance with the wishes of the owner. The first step is to decide on the type of sprinkler heads to be used. The system should be designed for complete coverage. Sprinklers should be selected on the basis of the type of area to be covered (ground cover, shrubs, lawn), the water flow rate and pressure available, soil infiltration characteristics and the scope of the area to be covered.

The sprinklers must be fitted to the area and carefully placed within the maximum recommended spacing (this is usually 50-60% of the diameter of coverage). If it is possible, triangular spacing of sprinklers should be selected over rectangular since it provides better coverage. Full circle and part circle coverage patterns also should be selected where appropriate. In many residential areas there is not enough space to establish a typical rectangular or triangular pattern for sprinklers. In such cases it is best to select the sprinklers for the bordered areas such as buildings, sidewalks, walls and patios first and then fill the middle areas with sprinklers so that uniformity of application will be sufficient.

An irrigation system should be designed with separate zones for different vegetation with different water requirements or different root depths. For example, flower beds should be watered separately from lawn areas. This requires additional pipe, fittings, sprinkler heads and valves. This type of refinement for watering will increase the initial cost of the system, but it will often result in a savings of water and the possibility of supplying different amounts of water for different plants.

It is important to keep in mind that for uniformity reasons, sprinklers with different application rates and different watering patterns should be placed in separate zones. If full-circle sprinklers are in the same zone with half-circle sprinklers, the nozzles for the half-circle sprinklers should be selected so that the flow rate is half of the flow rate from the full-circle sprinklers.

Most sprinklers have a decreasing application rate from the sprinkler head out to the maximum diameter of throw. This occurs because the area to be covered increases as distance from the sprinkler increases. Because of this pattern it is necessary that sprinklers overlap in order to achieve a uniform application. A safe rule of thumb is to make sure that the last droplets of one sprinkler reach the adjacent sprinkler. This is a 50% overlap of wetting patterns. Proper overlapping of the sprinklers will provide increased uniformity in water distribution over irrigated areas. Poor uniformity will result in some areas being over-irrigated and some areas being under-irrigated which could result in plant stress.

For more information and charts go to: http://edis.ifas.ufl.edu/WI003
Irrigation of Lawns and Gardens. Dorota Z. Haman, Gary A. Clark, Allen G. Smajstrla. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: May 1989.