Aquacraft IrriService: glossary of terms used

Distribution uniformity – measures how evenly water is applied to your landscape. Ideally, your sprinkler system should apply equal amounts of water to each square foot of the zone being irrigated resulting in a distribution uniformity of 100 percent. However, in the real world there are many factors that result in a lower distribution uniformity, such as improper sprinkler head spacing, blocked or clogged sprinkler heads, mismatched sprinkler nozzles, or tilted sprinkler heads. Overwatering is often the consequence of low distribution uniformity and can result in high water bills and potential damage to valuable plant material and structures.
  

Evapotranspiration (ET) – is a measure of the amount of water that transpires from the leaf surface and the moisture that evaporates from the soil surface. ET is affected by solar radiation, air temperature, wind speed, and relative humidity. Reference evapotranspiration (ETo) is the amount of irrigation required by a reference crop grown under weather conditions that are nearly identical to the weather conditions in your landscape. Irrigation replaces the amount of water lost from the soil and plants due to evapotranspiration (ET). Information about the ETo in your area is available from several sources and will be used in conjunction with other information that we learn about your landscape to develop an irrigation schedule and the theoretical irrigation requirement for your site.

Flow trace diagram – is a graph of the flow rate through the water meter over a period of time. This can be used to determine the flow rate of each zone in your irrigation system in gallons per minute.  
  

 

Historical irrigation application – is the amount of water applied to your landscape during the irrigation season in several previous years. The irrigation season is typically measured from March through October and can easily be calculated from your water bill.

Irrigation efficiency – is a calculation of the percentage of applied water that is available to the plant through the root zone. Watering too long can result in wasted water through runoff, or deep percolation through the soil even when the system has high distribution uniformity. Watering when it is windy or raining and applying more water than a particular plant material also requires results in poor irrigation efficiency and wasted water.

Landscape coefficient – is developed for your landscape from information obtained during an audit such as irrigated area, plant material, density of the plant material, and microclimates. The landscape coefficient is multiplied by the reference irrigation requirement to determine the theoretical irrigation requirement.

Microclimate – is a local area where the climate varies from that of surrounding areas due to a variety of influencing factors. Reflected heat from a building, a plant or structure that provides protection from the wind, or a low spot that collects rainfall, help to create the microclimates in your landscape.

Precipitation rate – is a measure of the rate at which water is being applied to the landscape from your sprinkler heads. Typically measured in inches per hour, the precipitation rate is affected by several factors, including water pressure, sprinkler type, sprinkler head spacing, and manufacturer. Determining the precipitation rate is critical in determining the schedule for your system since many sprinkler heads can apply water at a faster rate than the soil’s intake rate.

Reference crop – is the plant material used to measure the amount of irrigation required to replace the water lost from the soil and plant due to local weather condition. In Colorado, typically, the reference crop is a cool season grass (usually Kentucky bluegrass), well-watered and maintained at a height of 5 inches.    
  

Reference irrigation requirement – is the amount of irrigation applied to the reference crop to replace the moisture lost as a result of ET . Adjustment factors are applied to the irrigation requirement for the reference crop to determine how much water is needed for the various types of plants in your landscape. For example, your lawn, maintained at a height of 3 inches will require 95% of the irrigation applied to the reference crop while your shrubs may only require 67% or less.

"Smart" irrigation controllers – are irrigation controllers that have the capability of responding to real time weather and soil moisture conditions. These controllers self adjust their schedules to match the irrigation to ET. More about "smart controllers".
  

 

Soil or rain sensors – are devices that interrupt the signal to your irrigation controller and prevent irrigation from taking place for a certain period of time. Most sensors are wired into your existing irrigation controller however, a few companies offer wireless versions. Rain sensors can be adjusted to shut off with rainfall events ranging from 0.1 to 1 inch. Contacts inside the sensor open when rainfall is detected and close again when they dry out. A soil moisture sensor is designed to detect the available moisture in the soil. It should be installed in a representative area of the landscape and will prevent irrigation until the soil moisture drops below a set threshold level.
  

Sprinkler types – Each time your system is scheduled to irrigate, water flows though the pipes and is distributed on your lawn and other plant material by the sprinkler heads.   The sprinkler heads are designed to apply water over a certain area and they are typically laid out in a grid pattern. The two basic sprinkler types are fixed spray heads and rotors. During the site inspection, the type of sprinkler found in each zone will be noted – mixing different types of sprinkler heads on the same zone can result in poor distribution uniformity and low irrigation efficiency.

Fixed spray heads – typically provide a spray radius between 3 feet and 15 feet and are often used in small and/or irregularly shaped areas. The precipitation rate of fixed spray heads varies from 1.0 to 2.5 inches per hour and is dependent on the system pressure, spacing of the spray heads, manufacturer specifications, and nozzle size. Typically, fixed spray heads are stationary and have no moving parts other than the “pop-up” stem in the center of the sprinkler head. The height of the pop-up is determined by the irrigated plant material and generally ranges from 2 inches to 20 inches.
Rotors – distribute water in an arc pattern typically ranging from 40 ° to 360 ° .   The spray radius for most rotors is 20 feet to 150 feet with a precipitation rate between 0.1 to 1.5 inches per hour. Impact rotors are typically very durable and designed to provide irrigation to large areas. The radius and arc are easily adjusted however they often require regular maintenance and the spring mechanism is often too noisy for residential sites. Gear-driven rotors are quieter than impact rotors and typically require less maintenance because the design prevents clogging of the drive mechanism from dirt and other debris.  

Theoretical irrigation requirement – is a calculation of how much water should be applied to your landscape based on the irrigated area, the plant material, the local ET and the efficiency of the system. The theoretical irrigation requirement will be developed based on an irrigation system that is in good working order with a reasonable level of efficiency. Poorly adjusted and inefficient irrigation systems will always apply more water than is required for maintaining a healthy landscape.