Landscape architects use their experience and training to design environments with the proper selection of plant material. It is our forte. No other design professionals are so qualified to specify plant materials. But clients also expect irrigation to be included in the landscape architect’s construction package—along with the planting design.
Irrigation is seldom designed by the firm responsible for the planting, which means the need to hire an irrigation designer. This consultant becomes your responsibility for the professional aspects of the project. The purpose of this article is to help landscape architects understand the need to properly coordinate with the other professionals on the design team, the civil, plumbing, and electrical engineers. This article also discusses the two methods used to create an irrigation design, contractual obligations, and construction observation.
An early site visit lets you inspect for proper depth of the trenches, note how the crew respects any existing trees, see the labeling on the pipe, and how equipment is stored. Your fee should include time for construction observation—the amount will depend on the distance from your office.
As stewards of the land, it is our responsibility to be certain that any irrigation system we are associated with is properly designed, specifies state-of-the-art equipment and provides the most efficient use of water possible. Only three percent of the water on earth is fresh, and only 0.3% of freshwater is available for human use.
Today’s world problems revolve around oil. Water is next. Clearly, the lack of fresh water is becoming more serious every year, particularly in third world countries. For many years in the drier regions in the United States, communities restrict the use of municipal water on a regular basis.
A well-planned and carefully-installed irrigation system is an aesthetically-pleasing addition to a site. This view shows a new shopping-center complex in Tustin, Calif. where contractors have just installed plant material, mulch, controllers and stainless-steel enclosures.
Through the course of a project, when do you usually first think about irrigation design? If you are like many landscape architects, you are not likely to give it much thought until you are halfway through a project. This is understandable because irrigation is an engineering system that cannot be designed until the site plan, including the planting areas, are well defined, and the plant types named. This article will hopefully influence you enough to begin thinking about irrigation design earlier in the design process It is to your benefit and the others involved, as well as the project itself. Let’s start with the basics.
Landscape architects collaborating on irrigation projects should plan at least three site visits per job. They should occur after the installation in underway and the crew is on site at work so you can watch if it is following proper procedures—such as giving the solvent-welded pipe a twist when inserting it into a fitting. Photos by Erik Skindrud
When preparing your proposal for professional services, ask your prospective client if an irrigation system is desired. If so, then ask if a full-service design is required or a design-build system. Regardless of the approach, the landscape architect is responsible for the creation of some form of irrigation drawing addressing these issues.
For the full-service professional irrigation designer, your effort usually involves marking-up drawings by hand with notes on a reasonably-complete planting plan. You need to provide an appropriate computer-generated base for the actual design documentation.
The ganging or manifolding of valves has advantages during installation and makes for easier maintenance. There are fewer valve boxes, but this method typically requires longer wire runs to the controller.
For the design-build method, the same information will need to be documented, but this time, it must be computer-generated because your plans must be included in the construction documents. The drawings for both approaches should contain the following, at a minimum:
- Limit of Irrigation: This is sometimes obvious, but it is usually necessary to show a line illustrating the boundaries of the irrigation, meaning the area to receive water from the system.
- Limits of Spray and Rotary Sprinklers, vs. Quick Coupling Valves: Usually differentiating between spray and rotary sprinklers is not necessary because the planting plan will usually guide these decisions, mostly due to the sizes of the areas. However, it is not uncommon to indicate quick couplers outside of the limits of the automatic irrigation system for limited watering needs. Areas which may be watered using drip irrigation should also be identified. This information (usually coordinated with the client) must be marked on the plan, and discussed with the irrigation designer to work out the details.
- Point of Connection (POC): This must be identified for both design methods. Again, full-service by hand, design-build by computer. Both approaches will also need the available flow rate (gallons per minute, or gpm), and the pressure (pounds per square inch, or psi) in order to design the system.
- Controller Location, Wall Mount or Pedestal: The general location should be shown on both types of plans as well as the type on mounting.
- Special Conditions: Both methods require information about any conditions, such as underground obstructions, areas over structures to receive irrigation, isolated planting areas, tree pits, or pots with a note stating whether these areas are to be irrigated. Roof gardens are important to identify with their elevation change from the main system and whether they are intended to use the same POC.
The top of the valve box should be set no more than 1/2
inch above finish grade with the valves centered with good access on all sides and between to allow easy access if a valve must be removed for servicing. However, the valve box should not be in direct contact with the main line. A large riding mower could push the box against the pipe and cause problems over time.
If you determine a full-service design is required, you should include a fee from the professional irrigation designer. Often there is a limited amount of time between when you should hire a designer and when your documents are complete enough for him to execute his work before the construction documents are due. Be cognizant of this, since the timing of each project is different.
Specify three to six inches of local gravel for the bottom of valve boxes. There should be enough extra wire at each valve so wire connections can be serviced out of the valve box.Photos courtesy of Pam Noren, The Toro Company
In addition to all the information stated above, you must provide an electronic base for the designer’s use, a complete planting plan with plants labeled or keyed to a plant list, and a grading plan. The planting plan need not be 100 percent complete, but it must have the areas with shrubs and/or groundcovers clearly defined from the turf areas.
Today’s controllers are mostly solid state with multiple programs and sensor-ready LCD read outs allowing a near-infinite number of start-stop and program options. Battery back-ups save the programs during power failures. Note the second set of hinges allowing access behind the panel where the wires connected to the remote control valves are connected.
This is needed because these two different plant types require different precipitation rates and require separate remote-control valves. Precipitation rate is the inches of water per hour. Plant quantities are not important, but the areas of different species and/or plant types are important. Designers need to know if they can spray over the top of plants, even when mature, if they need to spray underneath, or if they need to consider a drip or bubbler system that emits water without spray and is more water efficient.
A remote control valve with a single station battery operated controller for areas that do not have 110-volt power. Remote systems run with a standard 9v battery that needs to be replaced once a year.
Given this information, the irrigation designer will be able to provide complete drawings, construction details, and a complete system specification. In addition, an irrigation designer will usually provide a chart with symbols identifying each nozzle along with other pertinent information and general notes, tailored to the specific plan. Remote control valves, quick coupling valves, and other equipment will be identified by model number and located on the plans for a complete integrated system, making it fully biddable with every detail specified.
Here’s a brass remote-control valve with pressure regulation attached. Brass valves are used to cope with higher static water-pressure conditions.Photos courtesy of Pam Noren, The Toro Company
The design-build approach should be considered if you know prior to submitting your proposal that the fee is going to be inadequate for what is expected of you, or the job is small, such as residential or small commercial project with few complexities. However, it is advisable to inform the client up-front you will be using the design-build method in your documents to eliminate any possible misunderstanding when is comes time to bid the project. Advise him or her there will still be a biddable irrigation plan defining the limit of irrigation, the types of irrigation, such as, spray, rotary, drip, and a point of connection, as well as a complete specification requiring the system be designed by a registered or certified irrigation designer.
Irrigation plans need to carefully portray the positions of valves, irrigation lines, controllers and other details to ensure contractors place each item accurately.
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Using the design-build method, a complete irrigation design still needs to be created. It is, however, in the form of a shop drawing submittal, an all-important requirement in the specification, after the bid has been awarded. The design-build contractor will need all the same information outlined in the full-service section above. It is extremely important to require qualifications as a submittal in your design-build specification. Require statements about years in business, certifications and successful completion of projects of similar size.
Landscape architects should attach detail drawings to plans to explain valve assembly details.Images courtesy of EDAW Irrigation Design Office
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There is a natural tendency to cut corners when bidding a job, so the contractor will likely rough out a design and take the remaining quantities. However, if your specification states the entire site must be accessible with quick couplers, but you fail to specify they are to be no more than 100 feet apart, you have little to fall back on when a shop drawing shows up with quick couplers spaced at 200 feet apart!
Close up of a large radius rotary for an athletic field. Heads specified for an athletic field should have standard rubber covers. Some manufacturers have heads mountable below grade.
Another important requirement is stating an acceptable coefficient of uniformity. Some of this information can be on your irrigation plan, but a considerable amount of the controlling factors and details should be in the design-build performance specification.
This spray nozzle is attached to an extended riser that lets it send water over the shrubs below. As the plants grow, the riser will need to be swapped out for a shorter model and a low angle nozzle that will spray under the plants. Photos courtesy of Pam Noren, The Toro Company
The specification should identify manufacturers you find acceptable, and a procedure for submitting substitutions. It must contain a listing of all the particular features you want to have on the system, such as brass, glass-filled, or plastic remote-control valves, brass or PVC isolation and gate valves, pipe specifics referencing all the appropriate ASTM sections, wire type and size, splicing connectors, valve boxes, solid state or electro-mechanical controllers, rain and freeze sensors, and many other options. The specification should also require a one-year warranty, and include all the specifics regarding the actual installation methods.
The nozzle in operation above, is perched on an extended riser that resembles the tall one seen here. One of the two shorter risers seen in this view will send water under the shrub’s foliage when it grows taller. Note that all three risers retract to ground level when not in use.
Photo: Erik Skindrud
Whichever method you use, full service or design-build, your fee must include time for irrigation-coordination work (and often time for construction observation), depending on the geographic location of the project, you, and the irrigation designer. Since you need to perform the coordination between all the consultants, you must consider this effort when developing your design fee.
Trenching operations should be deep enough to allow for multiple pipes and wire bundles. Depth of trenching depends on the diameter of the pipe being installed. Typically, 24-inches of cover is required of most mainline piping and 12 to 18-inches for lateral lines. Photo courtesy of Pam Noren, The Toro Company
Jon Pearson is the East Region Technical Director for EDAW based in Alexandria, Va. Special thanks to EDAW’s Greg Hurst and Brent Jeffery and to Jim Laiche of The Toro Company for contributing to this article.