What can farmers expect from irrigation system designers?
by Ian de Jager.
The design of an irrigation system, according to the design norms of South African Irrigation Institute (SABI), the choice of efficient equipment, the installation of the system according to plan, as well as the efficient management and maintenance of such a system by farmers are all important factors, if producers and farmers want to utilise available water resources optimally and conserve water.
- It is, therefore, of concern that many farmers make decisions based primarily on capital costs of the system.
- Farmers should consider using SABI’s Approved Designers, who have theoretical as well as practical knowledge of design.
- The correct questions should be asked by producers/farmers to ensure that the design specifications of the selected system fulfill his or her needs.
- It is advisable that farmers discuss the aspects detailed in this article with their irrigation consultant and supplier before purchasing a new system.
- The discussion will be beneficial to both parties and assist in making an informed decision on the intended capital investment. In these preliminary discussions, the duties and responsibilities of both should be made clear.
Designer qualifications
- What qualifications and experience does the designer have? (these would typically include: formal training from a university or technical college, SABI courses, SABI Approved Designer membership status, and/or registration with ECSA (Engineering Council of South Africa).
- Is he/she able to contactable provide references for similar systems and/or supply of materials?
Remuneration of consultant/designer
SABI Council suggests that all members of SABI should be remunerated for any professional work done for or on behalf of a client. There are no free designs, as eventually somebody must pay the time and effort involved in designing or specifying an irrigation system. Therefore, SABI urges its members to charge a fee for services rendered even if it is a nominal fee. The principle of paying for good service and advice should be implemented in the best interest of all parties involved in the irrigation industry.
Further information that buyers must obtain
- Does the intended irrigation activities comply with the National Water Act?
- Good planning must be done regarding the availability and requirements of water for the planned crop and the irrigated area.
- Equally important is that a quality analysis of the water that is used – this is necessary to ensure a suitable system is designed with no negative effects on the crops or blockages etc.
- A soil examination and analysis regarding the physical and chemical characteristics of the soil is also required.
- The above information must be discussed with the consultant/designer.
What the irrigation designer/consultant should provide
- A signed agreement that the system has indeed been planned according to the SABI norms (motivation should be provided if the designer diverted from the norms)
- A suitable topographic survey
- A detailed technical design and report in which flow rates and pressures are specified.
- A scaled layout plan.
- Detailed installation plans of the system.
- Detailed product specifications (and tender documents, if required) that will be used for purchasing, installing and/or commissioning.
- A suggested management plan of the system – it is important that the designer and the producer, from the preliminary stage, communicate clearly to prevent any misunderstandings and to ensure that the producer understands the management inputs and maintenance requirements of the planned system well and agree with it. Only when concurrence has been reached on the matter should the planning of the system proceed.
- A capital versus running costs comparison as well as the expected maintenance costs over the lifespan of the system: in this way, the producer is informed of the expected benefits and costs
Design materials/system
- What is the expected lifespan of the material that will be used?
- What are the possibilities of extensions to the system?
- Which components are of critical importance and should get special attention?
- Has adequate provision been made for the requirements of the Occupational Health and Safety Act’s influence on the system?
System specific norms
- What is the design Emitter Uniformity / Distribution Uniformity of the system?
- Is the system easily adaptable to variable water requirements such as seasonal changes and what is the impact thereof on the management inputs?
- What about a suggested maintenance program for the system components, especially for electronic or hi-tech equipment?
Water requirements
- What is the peak daily requirement of the crop in mm/day? Has the system capacity been adjusted to make provision for this?
- What is the expected water usage per year in mm/ha?
- If different crops/cultivars/ages/root stock will be used, is the system planned as such to comply with the specific requirements of each block?
- Has the designer provided a pump curve that shows the flow rate versus pressure for the specific pump/motor combination? Has this curve been discussed with the producer?
- Has the pump installation been checked for secondary losses, especially on the suction side, to ensure NPSH requirements are met?
- What are the expected energy costs of a system in R per mm and water supplied in R per ha?
Filtering
- Is filtering necessary and if so, to what extent – and what type of filter is suggested?
- Will the filters backwash automatically or manually?
- How often and for how long must the filters be backwashed?
Flow measurement
- Is the system fitted with a flow measuring device?
- Can it measure the flow rate as well as a volumetric total?
- Does the installation follow the manufacturer’s minimum installation instructions?
Pressure/air release and rinse
- Has sufficient provision been made for air outlet or inlet vales, pressure relief and scouring valves?
- Is water hammer expected and has provision been made to protect the system?
- Do the components and pipes have the correct pressure rating to match the expected operating conditions of the system?
- Has provision been made for the flushing of micro and dripper lines?
Guarantees
- Who will be responsible for what part of the guarantees – who will install, test and commission which system components?
- Which measurements and tests will be done to determine whether the system complies with the design specifications?
- Has the designer provided all the literature, guarantees and operating rules for the system?
Chemical injection
- Has provision been made in case a pipe burst occurs in one of the supply lines.
- Does the application rate of the equipment adapt to the system’s pressure and flow conditions?
- Can the equipment handle both chemicals and applied plant nutrients if necessary?
Control tests and measures that should be done after the system starts to operate:
- Read and keep record of specific electric current (Ampère) and pump pressure for each set-up.
- Keep records of pressures at each block or control valve.
- Keep records of the flow rate for each block, if available.
- Keep records of the pressure differences over the clean filter bank, if applicable.
- Check the inlet pressure at each block against the minimum pressure requirements as per the design report.
- This information can be used to periodically check the system’s performance.
Installation
Much difficulty and upset can be avoided if the parties agree beforehand about responsibilities regarding the following:
- Arrangements regarding site clearing, e.g. bulldozers.
- Pegging out of the system.
- Civil works.
- Electrical installations and applications.
- Provision of water, cement, sand and stone for thrust blocks.
- Supervision of the correct installation of equipment.
- Installation of the equipment inside the pump house.
- Who is responsible for equipment that fails?
- How often will the designer visit the site to ensure that equipment and installation comply with the requirements?
If problems occur during the testing of the system, the producer and the designer need to come to an agreement on how the system must be improved to comply with the design specifications. The system may not function properly because of installation mistakes by the producer or design mistakes by the designer. If the farmer/producer made the mistake, he/she must carry the cost of the alterations and vice versa.
SABI believes that the above suggestions are acceptable to farmers and designers and will lead to less misunderstandings as well as an improvement of the irrigation industry and water use in South Africa.
