Glossary of Irrigation Terms

The amount of water pressure lost as water travels through an irrigation system. The head loss of a specific system can be divided into major head loss; caused by friction in the pipes themselves, and minor head loss; caused by components such as vales, backflow preventers, bends and tees.

HDPE is high-density polyethylene, a polymer made from petroleum. It's extremely versatile, durable and flexible. Its properties make it very useful for large irrigation projects where its flexibility can cope with sharper bending radii for example and the kind of fluctuations in pressure, movement and external factors like UV rays and heat or cold, more easily than PVC. Because the joints are heat-fused, they are extremely strong and are more likely to create a leak-free system.

All irrigation systems lose a small volume of water via evaporation, water run off or leakage. The gross capacity of an irrigation system is a measure of its ability to deliver sufficient water after all such losses are taken into account.

Galvanization is the process of applying a coating of zinc to iron or steel to prevent corrosion. Most commonly, the metal to be treated is hot-dipped by submersion in a vessel of extremely hot, molten zinc.

Friction factor is used when calculating the pressure loss in an irrigation system caused by friction. This friction can be between the water and the inner surface of the pipes, and is influenced by factors such as the length and diameter of the pipes, as well as the material used and the inclusion of fittings such as tee or elbow joints

The means by which nutrients are applied to the landscape via an irrigation system. For example irrigation water can be diverted to a tank of fertilizer where it dilutes the product and then rejoins the pipeline. 

Emission uniformity  tells you how evenly water is being discharged by all emitters in a specific irrigation or micro-irrigation system. To calculate emission uniformity, take the average discharge of the 25% of emitters with the lowest discharge rate, and divide this by the average volume discharged across all emitters in the system. Higher emission uniformity equates to a more efficient irrigation system.

Deep percolation occurs when excess irrigation water penetrates the soil and percolates below the root zone of any vegetation planted there. The deep percolation percentage is the ratio of the average depth of water below the root zone to the average depth of irrigation water overall, with a higher percentage generally reflecting greater water wastage.

A region that's considered subhumid is not the opposite of subarid! As a general rule, a region is subhumid when it experiences moderate rainfall - more than 20-inches but less than 40-inches annually - and a moderate to high evaporation potential.

As its name suggests, a region that's considered semiarid is neither completely humid nor arid. As a general rule, a region is considered semiarid if it normally experiences an annual average of between 10 and 20-inches rainfall.

A characteristic of a region with a humid climate is high rainfall and a low evaporation potential. As a general rule, a region is considered humid if it normally experiences an annual average rainfall of more than 40-inches.

A characteristic of a region with an arid climate is low rainfall and a high evaporation potential. As a general rule, a region is considered arid if it normally experiences an annual average rainfall of less than 10-inches.

Sometimes called a uniformity coefficient, this is a measure of how evenly irrigation water is applied across a specific area of landscaping. To calculate, take the average depth to which irrigation water infiltrates the soil, subtract the average deviation from this depth, and then divide the result by the average depth to produce a percentage measurement.

A centrifugal pump consists of a pump with an impeller (rotating vanes) and either an electric motor or engine. The rotational energy the motor creates is converted to the hydrodynamic energy of the water as it flows.

Many factors influence the amount of water needed by plants. The Blaney-Criddle Method is a formula used to estimate water loss due to evapotranspiration in crops. At its simplest level, the calculation takes into consideration such factors as consumptive water use, mean monthly temperatures, and percentage of total annual daylight hours that were available over the period being measured. There are several other formulae employed to assess the amount of water plants need and it's an important aspect of the science of irrigation - whether in agriculture or for domestic and leisure purposes. Given the growing need to conserve water supplies and the increasing number of restrictions governing how much water we use for irrigation, knowing how much and when to water is a critical aspect of landscape management.