This article by A. Smajstrla, F. Zazueta, and D. Haman of the University of Florida appeared in “The Vegetable Growers News,” April 2001.

he improper design of irrigation systems can have several consequences. The consequences can be divided into those affecting public health, waste of natural resources, water pollution, operator safety, and economic factors, including cost of irrigation, economic return from irrigation, and irrigation system life expectancy.

 

Public health

When chemicals are applied through irrigation systems, failure to properly design, install, and manage backflow-prevention equipment can result in the backflow of chemicals and the pollution of water supplies. Likewise, failure to properly select prevention equipment could result in its failure to function properly. Both Florida law and Environmental Protection Agency regulations require that backflow-prevention equipment be installed when chemicals are injected into irrigation systems.

If the irrigation water source is a municipal or other public drinking water supply, backflow of water from an irrigation system can contaminate the water supply even if chemicals are not injected. Therefore, backflow-prevention devices must be installed on all irrigation systems which use these water supplies. County or municipal codes specify the types of prevention devices required to prevent the possible contamination of these water supplies.

 

Wasted water

Poorly designed irrigation systems which apply water non-uniformly will waste water and chemicals applied with the water. Some areas will be over-irrigated, while others will be under-irrigated. If the system manager applies the correct average amount of water, the under-irrigated areas will suffer yield or quality reductions due to water stress, while yield or quality reductions due to leaching of water and chemicals will occur in the over-irrigated areas.

With non-uniform irrigation systems, if sufficient water is applied at each irrigation to assure that none of the crop is under-irrigated, most portions will be over-irrigated. This will increase the waste of water and chemicals. Also, the fuel required to pump excess water and to produce and inject excess chemicals will be wasted.

 

Water pollution

Excess applications of water and the resulting leaching of chemicals can result in the pollution of surface or groundwater supplies. Leaching can readily occur through sandy soils. Water pollution can occur both as a result of inefficient applications of chemicals and from leaching.

It is often difficult to determine the economic and environmental effects of water pollution, because it is difficult to measure, and because the impacts of various pollutants on the environment are often unknown. It is also impossible to completely eliminate the potential for water pollution, because chemicals are required in the root zones and on the foliage of plants. However, the potential for water pollution can be minimized.

Proper irrigation-system design and management can minimize leaching and water pollution, because a well-designed and well-managed irrigation system can properly apply only the required amounts of water and chemicals.

Chemigation systems, irrigation systems that are designed for chemical applications by injection with the irrigation water, have great potential for reducing water pollution from irrigated lands.

 

Operator safety

The safety of the operator and others in the area can be affected by the improper design of an irrigation system. Electrical circuits must be properly designed and installed to avoid shock hazards in a wet environment. Power units and drive units must also be properly sized, mounted, aligned, and shielded to assure safe long-term operation. Chemical injection systems must be properly designed and installed to avoid operator contact with chemicals.

To ensure that systems will function safely, irrigation-system components must be properly pressure-rated. Pressure-relief valves and safety equipment must be installed. All components must be installed according to specifications.

 

Cost of irrigation

To minimize the cost of irrigation, the designer must consider the total cost, which is the sum of the annual fixed and operating costs. Irrigation-system cost is directly affected by the quality of design. In general, well-designed systems have greater initial costs than poorly designed systems. This occurs because larger components, including larger pipe sizes, are required to minimize pressure losses and achieve uniform water applications. However, operating costs of well-designed systems will usually be lower. Pumping, labor, and other operating costs will usually need to be increased to compensate for under-designed irrigation systems. These factors will almost always make the total annual irrigation-system cost greater for a poorly designed irrigation system, as compared to a well-designed system.

An irrigation system designer must consider existing production practices, availability of labor, and the convenience of the irrigator in each design. Proper consideration of these factors will help to minimize costs by the specification of irrigation systems which are readily managed within a given production system and which use existing labor efficiently.

 

Economic return

Poor irrigation-system design can result in the construction of irrigation systems that cannot provide the necessary soil-water-nutrient environment for optimum crop growth. This will result in reduced yields, reduced quality, or higher costs per unit of production, when compared to well-designed irrigation systems.

 

Life expectancy

The life expectancy of a poorly-designed irrigation system may be much shorter than that of a well-designed system. As examples, the use of components that are not adequately pressure-rated, that are not resistant to chemicals being injected, or that are not otherwise properly installed or matched to the system, can result in early system failures.