Standards
Irrigation System Design and Water Conservation - Standards
Introduction
These design and usage requirements are necessary to conserve water and ensure plant health. Water and maintenance expenses can be reduced when these irrigation system design requirements or designs with similar performance standards are implemented and maintained.
_________
Designer Qualifications
Irrigation designer shall be a Certified Irrigation Designer (CID) as certified by the Irrigation Association, or other professional with extensive experience in the design of commercial irrigation systems.
Irrigation Design Plan
An irrigation design plan shall be submitted and approved by the client. The irrigation design plan shall accurately and clearly identify:
- Property boundaries
- Locations, model and size of all components of the irrigation system
- Static water pressure at the point of connection
- Flow rate, zone number, application rate (inches per hour), and design operating pressure
- The square footage of turf and planting beds on the plans
- Site water requirements
- A pressure loss worksheet
- Annual water usage calculation in gallons
Flow Requirements
Water requirements for each site must be determined prior to designing the system in order to size the system for adequate capacity. System capability to provide sufficient water for adequate plant growth during the summer when evapotranspiration (ET) is highest (“peak demand”) is an important consideration. This “peak demand” system design calculation should be based on a 3-day per week water restriction scenario. Peak demand will be based on 1.95-inches per week based on historical climate data.
Pressure Control
In order to control pressure and protect the system from damage, pressure reducing valves shall be installed immediately downstream of the backflow preventer if static pressure is 35 PSI or more above the system design pressure. System design pressure is the required operating pressure at the head plus system pressure losses.
Pressure at all heads should be within 10 percent of the system design operating pressure. Example: A head designed for 50 PSI should operate within the 45 to 50 PSI range. This shall be accomplished by using pressure-reducing control valves or a pressure reducing system in the base/stem of the head. Accurate pressure control is critical for good system performance.
Sprinkler Head Layout
Head spacing shall not exceed 50 percent of the diameter of its effective coverage. Part circle heads must be used around the entire turf/bed perimeter to avoid overthrow onto buildings, asphalt, concrete, etc. Walks of four feet or less with planting on each side may be sprayed over.
Radius reduction at the head shall not exceed 25 percent of the maximum arc as indicated in manufacturer’s catalog. If there are coverage problems in unique areas, use part circle “backup heads” where there is not enough space for another row of full circle heads.
- Slopes in excess of a 3 to 1 ratio – Sprinklers at the top of a slope will be zoned separately from those at the bottom of a slope in order to reduce run-off and control water application across the slope. All sprinklers on sloped areas will be equipped with check valves to prevent low-head drainage.
- Lateral lines on slopes shall be installed along the contour rather than up and down the slope.
- Narrow Strips and Medians – If the area is less than 16 feet wide, use pop-up spray heads with a fixed radius MPR nozzle or rotary nozzle that does not exceed the width of the strip. If the area is less than five feet wide, irrigate with subsurface drip irrigation (SDI) or eliminate turf in favor of tree and shrub plantings.
Zoning & Control
Divide the site into areas that have the same water requirements such as turf, planting beds, ground cover, etc. Cultivated planting beds will require more water than areas that are mulched with bark or rock.
Identify any low areas as well as high solar and wind exposure areas and zone them separately from the adjacent areas. Heads, valves and mainline shall be installed adjacent to and outside of low areas.
All heads within the zone must have matched application rates, ie., bubblers, point source drip, rotors and spray heads must be zoned separately. Zones must be designed and nozzled to provide a uniform distribution of water.
Hydraulic Justification
The irrigation design should include a pressure loss worksheet for the zones with the highest flow and furthermost from the source. The pressure loss worksheet should list the following:
- Valve number and flow rate
- Available static water pressure
- Loss or gain due to elevation
- Detailed list of various component pressure losses & velocities
- System operating pressure requirements
Equipment Selection
Spray Heads: Pop-up spray heads for turf areas shall have a minimum pop-up height of 4”. A 6”
pop-up height shall be used for narrow strips and medians. The 12” pop-up height will be used in ground cover and flowerbeds.
Pop up spray heads shall have a pressure regulating device (set at 30 or 40-45 PSI, depending on the type of nozzle being used) installed in the base of the stem, a check valve to prevent low-head drainage and matched precipitation nozzles.
Gear Driven Rotor Heads: Rotors shall use an internal gear drive, closed case with wiper seals and heavy duty spring retraction. Pop-up height will be a minimum of 4”. All heads shall have check valves built into the bottom of the body. Pressure control should be done at the base of the head or at the valve.
Automatic Controllers: The controller shall incorporate the following features: Accurate timing in hours and minutes; eight repeat cycles; flexible day scheduling; sensor inputs; four programs; and a memory retention of at least ten years without power. Controller shall also utilize some form of smart water application technology to adjust the irrigation schedule daily in line with the water requirements of the landscape material and suspend irrigation during effective rainfall events.
Drip: Drip irrigation shall be zoned for varying plant needs, slopes and exposures. Point source traditional drip with pressure-compensating emitters is preferred in non-cultivated planting beds. Each zone shall be equipped with a pressure regulator and filter appropriate for the specified emitters.
_________
Performance Standards for Water Use
Each project should be designed to allow a maximum budget of 31-inches of water per square foot annually. Effective rainfall is not included in this total. This budget gives a project a maximum of 841,500 gallons/acre/year.
_________
Landscape Modifications
The irrigation design should include recommendations for landscape modifications to save additional water. Modifications will include the identification of high water use or poorly designed areas that could be modified to xeriscape to substantially improve the efficiency of the system.
References
Castle Rock Water Rick Schultz 720-733-6027
Aquacita Jason Mower 720-233-9698
Jeffco Open Space David Schott 303-885-4182
Professional Certifications:
- Irrigation Association
Certified Landscape Irrigation Auditor (CLIA) - Irrigation Association
Certified Commercial Irrigation Designer (CID) - ASSE
Certified backflow tester - Qualified Water Efficient Landscaper (QWEL)
Read more
Professional Affiliations:
- Irrigation Association
- EPA WaterSense partner
- American Society of Sanitary Engineering
