PPP Notes - Landscaping

LANDSCAPING

 

IRRIGATION

 

• Irrigation system design considerations include the water supply, site conditions, climate, and plant material selection.
• The available volume of the water supply is measured in gallons per minute (gpm).
• The available pressure of the water supply is measured in pounds per square inch (psi).
• Water supply can be from a public or private utility system, or can be pumped from a well or pond.
• Selection of irrigation equipment and sizing of distribution piping is based on available volume and pressure of the water supply.
• Site conditions that must be considered are topography, drainage, soil type, and solar exposure.
• Important climatic conditions include predominant wind direction, annual rainfall, and temperature variations.
• When irrigation systems are subject to freezing temperatures, precaution against damage to the system components from freezing must be built into the design.
• Planting materials have different requirements for water.
• In fact, variations of turf grass may have vastly different watering needs.
• Plant water requirements include water lost by evaporation into the atmosphere from the soil and soil surface, and by transpiration, which is the water actually used by the plan.
• The combination of these is called evapotranspiration (ET).
• Because turf grass has the highest rate of ET of any planting materials in the landscape, and because the ET of turf varies depending on the seasons, irrigation systems are designed to replace water lost at the highest level of ET for the turf grass in the landscape.

 

IRRIGATION SYSTEM COMPONENTS

 

• There are a number of common irrigation system components, among them:
• Backflow Preventer: Prevents water from the irrigation system from backflowing into the potable water supply.
• Controller: Acts as a timer that maintains status of the day of the week and time of the day in order to activate electric control valves at a specific day, and duration.
• Main Line: The primary pipe supply line that distributes water from the point of connection of the source of supply to the electric control valve.  Main line piping of sizes 2.5” diameter and larger are typically class 200 PVC.  Piping of sizes 2 in. and smaller are typically schedule 40 PVC.
• Electric Control Valve: Low-voltage solenoid-actuated valves that control the flow of water from the main line into the lateral line piping.  Electric control valves are activated by the controller.  Signals are sent from the controller to the valves through direct burial wires.
• Lateral Line Piping: The pipe supply line that distributes water from an electric control valve to a sprinkler head or a drip emitter.  Depending on the application, lateral line piping can schedule 40 PVC, class 200 PVC, or class 160 PVC.  Lateral line piping for drip irrigation is typically polyethylene tube.
• Sprinkler Head: A water distribution device attached to the lateral line piping.  Rotary and impact sprinkler heads are used to irrigate large areas and can be spaced from 20 to 80 ft. o.c.  Popup spray sprinkler heads are used to irrigate smaller areas and can be spaced from 5 to 20 ft o.c.  Sprinkler heads are used to irrigate turf grass or broad areas of low-growing shrubs or ground covers.  For optimum efficiency, sprinkler heads are spaced to provide overlapping head-to-head coverage.
• Bubbler Head: A water-distribution device used to irrigate shrubs and ground covers by placing water immediately adjacent to the plant, or by flooding a planting bed.
• Drip Emitter: A water distribution device that distributes water very slowly, in increments measured in gallons per hour.  Drip emitters are used to water individual plants.

 

COORDINATION CONSIDERATIONS

 

• Check the contract to ascertain that an irrigation system is to be provided.
• On rare occasions, it is an option, which should have been determined when signing the contract.
• An irrigation plan should show:
• Limits of irrigation
• Approximate limits of grass versus shrub and ground cover areas
• Point of connection (POC) for the water
• Controller location
• Grading plan
• Any out-of-the ordinary conditions (e.g., underground obstructions, areas over structure, isolated planting areas, tree pits, or pots) with a note clarifying whether there areas are or are not to be irrigated
• Coordination with the plumbing engineer should occur near the start of the construction documents phase, mainly because the services needed to supply an irrigation system are the same as those for the domestic water system for a building.
• These include the location of the water meter and any calculations for the gallons per minute (gpm) and pounds per square inch (psi).
• When working on a project that has a water meter room within the building, it is wise to let the plumbing engineer know (even as early as the design development phase) that a backflow preventer and an irrigation meter separate from the domestic water meter will be needed.
• Ask the plumbing engineer to show the POC 2 ft. beyond the outside face of the exterior wall, or vault at a depth of 18 in. below finish grade and with a cap.
• This is particularly important for commercial jobs where meter room is below grade and the exterior wall is likely cast-in-place concrete. 
• If the irrigation main supply shows on the plumbing drawings, this will ensure the pipe is installed in the wall properly, with a waterstop, and has a tight seal around the pipe.
• There is no need for the water and electrical power sources to be located near each other; they only have to meet at the remote control valves.
• There needs to be a series of wires (one for each valve, plus a central wire) going through an exterior building wall 18 in. below grade or through the bottom of the pedestal, which has to be mounted on a concrete pad.
• These wires should always be enclosed in a “sleeve,” which is usually PVC.
• Once outside, the wires should remain encased in PVC pipe until they reach a mainline trench.
• From there they go off in all directions to the remote control valves, which should be buried under the pipe in the same trench.
• Irrigation sleeves should be installed prior to paving operations, but after final subgrade elevation has been established.
• The controller is best located in a place out of view from the general public.