[Landscape Architecture & Construction]



People who manage or pay the water bills for sites with large irrigation systems are getting more and more interested in applying water efficiently.

In King County, the cost of water has risen considerably over the past five years and is projected to keep rising an average of at least 10 percent for each of the next five.

Water usage increases dramatically in the summer and water purveyors in the Puget Sound region have determined that his increase is due primarily to the use of water outdoors, with the majority used for irrigation.

Because of the limited opportunities to develop new water supplies and the need to supply water for the growing needs of the region, a reduction in summer peak use is not only advisable, but necessary. After extensive study it has been determined that conservation of irrigation water offers one of the most effective opportunities to help reduce this peak demand.

A well-planned irrigation system design is critical to the development of a water conservation program, and can reduce water use up to 40 percent if operated and maintained properly.

A good design reflects the irrigation equipment's's capabilities, the specific ares to be irrigated and the needs of different plant materials. There will be a separation of plant materials with different irrigation requirements, and irrigation equipment with different pressure and precipitation rates among microclimates within the site. Areas with slopes will be differentiated from flat areas and sunny areas from heavily shaded areas.

The same type of equipment should be used in each zone to provide consistent precipitation rates and coverage. Equipment such as rotors, which move at a constant speed, should be separated by spray patterns. For example, a quarter-circle rotor will put down four times the amount of water per square foot as a full circle rotor running for the same length of time.

A good design will also reflect the placement of obstructions such as trees, signs, telephone poles and any other objects which may compromise the spray pattern.

The maintenance of and irrigation waste directly influences the effectiveness and efficiency of the system.

A complete system checkout should be performed after every mowing. This checkout, conducted while the system is operating, would identify broken or plugged nozzles, broken or misalligned heads and broken lines.

If a mower ran over a head and broke it below the ground the damage would not be visible or noticed until the system was activated -- and if it runs at night, it might not be noticed until it develops a major problem and requires the scheduling of an additional trip to the site for repair.

Other maintenance practices which should be scheduled on a regular basis include cutting the grass away from the heads and checking pressure to make sure it is still within design guidelines.

All equipment repairs should be completed with identical equipment as originally installed. The use of different head or nozzle types can result in different precipitation rates and poor distribution.

The management of a site's irrigation system to conserve water can require specialized equipment and skills. Water auditing will determine a system's efficiency and provide a basis for schedule development.

Periodic adjustment of schedules is critical to compensate for current weather patterns. Applying the amount of water plants require is one of the most difficult design problems to achieve consistently. Irrigation schedules should be adjusted a minimum of one a month. Scheduling adjustments on a weekly basis will more closely reflect changing weather patterns and result in better irrigation efficiencies.

A well-managed irrigation system will not only save water, but will result in a healthier landscape and reduce the application of herbicides, pesticides and fertilizers.

Wayne Kennedy is the owner of Synergy, a water management company which specializes in the active management of irrigation systems.

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