By the end of this chapter, you will be able to:
Mastering these skills will help you ensure efficient, safe, and reliable irrigation and drainage systems on the farm—making a real difference in agricultural productivity and safety.
Compiled by: Bonface Omondi
Farm irrigation and drainage systems are fundamental to horticultural productivity in Kenya, where climate variability and seasonal rainfall patterns challenge consistent crop growth. Effective design of these systems ensures optimal water supply to crops while preventing waterlogging and soil degradation, which are critical for high-value horticultural crops like tomatoes, French beans, and flowers. This chapter explores the principles behind designing irrigation and drainage systems tailored for horticultural farms, enabling professionals to enhance crop yields sustainably and efficiently manage water resources.
Designing a farm irrigation and drainage system means planning how water will be brought to the crops and how surplus water will be removed, before any pipe or drain is laid. A good design starts from the farm's water source and water needs, the soil, the slope of the land and the crops to be grown. Where water is limited, as on many Kenyan horticultural farms, a poorly designed system wastes water, leaches nutrients and may cause salt build-up or erosion, while a well-designed one delivers the right amount of water at the right time and drains away the excess.
Precise terms keep a design team and a farm crew working to the same plan. The terms below describe the parts and purposes of the systems used in horticulture.
A system is a set of parts that work together for one purpose. A farm irrigation and drainage system includes the water source, the pump or tank, the pipes and channels that carry water, the controls and meters, the devices that apply water to the crop, and the drains that remove excess water.
Drainage is the removal of excess water from the soil surface or from the root zone, to prevent waterlogging, erosion and salt build-up. Roots need air, and soil that stays saturated deprives them of it.
Design is the process of planning the layout, sizes and components of the system, using the farm's water supply, soil, slope, crops and available money to prepare a plan that can be built and operated.
Water use efficiency, often called crop water productivity, compares the crop produced with the water used to grow it. It is calculated as yield divided by the water applied.
Example: a farm harvests 30,000 kg of tomatoes using 6,000 m³ of water. Water use efficiency = 30,000 ÷ 6,000 = 5 kg of tomatoes for each cubic metre of water. A higher figure shows better use of water.
Irrigation is the artificial application of water to the soil to supply the needs of crops when rainfall is too little or unreliable. It allows crops to be grown in dry seasons, makes yields more dependable, and can also carry dissolved fertiliser to the roots.
Surface irrigation is the application of water over the soil surface so that it flows and soaks in by gravity, with no pressure or nozzles. The water runs in furrows between rows, floods levelled basins or moves down a sloping border strip.
Sprinkler irrigation is the application of water by spraying it through nozzles under pressure, so that it falls on the crop and soil like rainfall. A sprinkler system is made up of a pump, a mainline, lateral pipes and sprinkler heads on risers.
A pivot, or centre pivot, is a long sprinkler pipe carried on wheeled towers that rotates around a fixed centre point, irrigating a circular area. It is a mechanised form of sprinkler irrigation.
Irrigation and drainage together manage the water in the root zone, which is one of the most important influences on yield and quality in horticulture.
A well-designed irrigation system supplies water in the right amount at the right time, whatever the rainfall, so that crops grow evenly and produce the yield and quality that markets expect.
Drainage removes excess water that would otherwise cause waterlogging, erosion and root diseases, and it carries away salts that build up in the soil where irrigation water is used. A farm on heavy clay soil depends on its drains in the long rains.
Soil that is neither too dry nor too wet allows nutrients to dissolve and move to the roots, so fertiliser is used well. Systems that apply fertiliser with the water, called fertigation, depend on a well-designed irrigation system.
Reliable water allows a farm to plant in the dry season, to produce for markets when prices are good, and to grow a wider range of crops. This increases farm income and food supply.
Efficient systems cut water losses by evaporation, runoff and leaks, so that more crop is produced from the same water. Under the Water Act, 2016, taking water from rivers, springs and boreholes is regulated and usually requires a permit, so a design must stay within the water that the farm is permitted to use.
Pipes and pumps deliver water to the field with less carrying and watering by hand, and timed or automatic operation frees labour for other tasks.
The type of system chosen depends on the crop, the soil, the slope, the water supply, the size of the farm, the money available and the skills at hand. The main irrigation types are compared below.
| Type | Capital cost | Water use efficiency | Suits |
|---|---|---|---|
| Surface | Low | Lower | Level or gently sloping land, with plenty of water, and crops grown in rows |
| Subsurface | High | High | High-value crops where water is scarce and the system can be well managed |
| Sprinkler | Medium | Medium to high | Closely spaced vegetables, nursery plants and many field crops |
| Trickle | Medium to high | Highest | Orchards, greenhouse crops, flowers and row vegetables |
| Centre pivot | Very high | High | Large, flat fields farmed at a large scale |
Surface irrigation distributes water over the soil by gravity, using furrows, basins or borders. It is cheap to build and needs no pressure, so it suits small farms with a source of water above the field, such as a canal. It uses water less efficiently, because the water can run off the ends of rows or soak below the roots, and the land must be levelled or graded carefully. As a drainage method, a surface drain uses open channels, ditches and graded field surfaces to carry excess rainwater and runoff away from the crop, which prevents erosion and ponding in heavy rain.
Subsurface irrigation supplies water below the soil surface, either through buried pipes with emitters or by raising the water table through ditches or perforated pipes so that water reaches the roots from below. Little water is lost to evaporation, the surface stays dry, which reduces weeds and some diseases, and there is no obstruction in the field. The system is costly to install and difficult to inspect and repair, and in salty conditions salts may collect near the surface. As a drainage method, a subsurface drain uses perforated pipes or tiles buried below the root zone to lower the water table and remove surplus water, which is important on heavy clay soils that stay wet for long periods.
Sprinkler irrigation sprays water over the crop through nozzles, and it can be adjusted to apply a light or heavy amount. It suits vegetables, nursery beds and many field crops and gives fairly even coverage on uneven land. Wind spoils the uniformity of the spray, water on leaves can encourage some diseases, and the system needs a pump and enough pressure.
Trickle, or drip, irrigation delivers water slowly, drop by drop, through emitters on pipes laid on or just below the soil, directly to the root zone of each plant. It wastes very little water, works at low pressure and can carry fertiliser. It suits orchards, greenhouse crops, flowers and row vegetables. The emitters can block, so clean water and filters are essential, and the system needs regular checking.
A centre pivot is a mechanised sprinkler system in which a long pipe on wheeled towers moves in a circle around a central point. It covers a large area with little labour and applies water uniformly. Example: a pivot with a radius of 200 m irrigates a circle of area 3.1416 × 200² = 125,664 m², which is about 12.6 hectares. It is costly, needs flat land and a large, dependable water supply, and it leaves the corners of a square field dry, so it suits large farms only.
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Create a free accountThis chapter explored the design of farm irrigation and drainage systems, starting with clear definitions of key terms such as irrigation systems, surface, sprinkler, and pivot systems. It highlighted the importance of these systems in enhancing agricultural productivity and managing water efficiently. Various types of irrigation and drainage systems were examined, including surface, subsurface, sprinkler, trickle, and centre pivot methods, each suited to different farming contexts. The chapter then discussed critical factors to consider when selecting an appropriate design, such as soil type, water availability, and crop requirements. Attention was given to the preparation of materials needed for constructing drainage systems, emphasizing the importance of quality and suitability. It also detailed the steps involved in assembling irrigation and drainage systems to ensure proper functionality. Finally, the chapter covered maintenance practices necessary to sustain the efficiency and longevity of these systems in farm operations.
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Pen | Reference Manual on Farm Irrigation and Drainage Systems |
| Foolscap | Personal Protective Equipment (Gumboots, Overall/Dustcoat, Face Mask) |
| S/N | Item | Quantity |
|---|---|---|
| 1 | Personal Protective Equipment (PPE) - Gumboots | 1 Pair per Candidate |
| 2 | Personal Protective Equipment (PPE) - Overall/Dustcoat | 1 Pc per Candidate |
| 3 | Personal Protective Equipment (PPE) - Face Mask | 1 Pc per Candidate |
| 4 | Writing Materials (Pen and Foolscap) | 1 Set per Candidate |
| 5 | Reference Manual on Farm Irrigation and Drainage Systems | 1 Pc per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: PPE and Preparation | |||
| Wore PPE correctly (gumboots, overall/dustcoat, face mask) as per workplace procedures (Award 1 mark for each PPE donned correctly or zero) | 3 | ||
| Assembled all required materials and tools for the definition task (Award 2 marks for assembling all materials and tools or zero) | 2 | ||
| Prepared writing materials and reference manual for use (Award 1 mark for preparation or zero) | 1 | ||
| Sub-Total | 6 | ||
| TASK 2: Define and Explain Terms | |||
| Defined and explained the term 'Irrigation Efficiency' correctly (Award 3 marks for clear and correct definition or zero) | 3 | ||
| Defined and explained the term 'Drainage Coefficient' correctly (Award 3 marks for clear and correct definition or zero) | 3 | ||
| Defined and explained the term 'Water Table' correctly (Award 3 marks for clear and correct definition or zero) | 3 | ||
| Defined and explained the term 'Infiltration Rate' correctly (Award 3 marks for clear and correct definition or zero) | 3 | ||
| Defined and explained the term 'Soil Permeability' correctly (Award 3 marks for clear and correct definition or zero) | 3 | ||
| Defined and explained the term 'Evapotranspiration' correctly (Award 3 marks for clear and correct definition or zero) | 3 | ||
| Defined and explained the term 'Surface Runoff' correctly (Award 3 marks for clear and correct definition or zero) | 3 | ||
| Defined and explained the term 'Capillary Fringe' correctly (Award 3 marks for clear and correct definition or zero) | 3 | ||
| Defined and explained the term 'Saturated Zone' correctly (Award 3 marks for clear and correct definition or zero) | 3 | ||
| Defined and explained the term 'Drainage Density' correctly (Award 3 marks for clear and correct definition or zero) | 3 | ||
| Sub-Total | 30 | ||
| PRODUCT CHECKLIST | |||
| All ten terms correctly defined with clear and accurate explanations (Award up to 4 marks for completeness and accuracy of definitions) | 4 | ||
| Sub-Total | 4 | ||
| GRAND TOTAL | 40 | ||
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Personal Protective Equipment (gumboots, gloves, dustcoat) | Water |
| Flip chart or whiteboard | Sample irrigation and drainage materials |
| Marker pens | |
| Notebook or foolscap | |
| Pen | |
| Sample irrigation tools | |
| Sample drainage materials |
| S/N | Item | Quantity |
|---|---|---|
| 1 | Personal Protective Equipment (gumboots, gloves, dustcoat) | 1 set per Candidate |
| 2 | Flip chart or whiteboard | 1 pc per Candidate |
| 3 | Marker pens | 3 pcs per Candidate |
| 4 | Notebook or foolscap for notes | 1 pc per Candidate |
| 5 | Pen | 1 pc per Candidate |
| 6 | Sample irrigation tools (e.g. watering can, hosepipe, drip emitter) | 1 set per Candidate |
| 7 | Sample drainage materials (e.g. drainage pipe segment 1m long, gravel sample) | 1 set per Candidate |
| 8 | Access to water source for demonstration | 1 source per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: Demonstrate understanding of the importance of farm irrigation and drainage systems | |||
| Wore PPE (gumboots, gloves, dustcoat) as per workplace procedures (Award 1 mark for each PPE worn correctly or zero) | 3 | ||
| Assembled all required materials and tools before starting the explanation (Award 2 marks if all materials/tools assembled or zero) | 2 | ||
| Explained at least five benefits of farm irrigation systems clearly with examples (Award 2 marks per correct benefit explained with example or zero) | 10 | ||
| Explained at least five benefits of farm drainage systems clearly with examples (Award 2 marks per correct benefit explained with example or zero) | 10 | ||
| Used sample irrigation and drainage tools/materials to illustrate points (Award 5 marks for demonstrating use of samples or zero) | 5 | ||
| Recorded key points of the explanation clearly in writing (Award 5 marks for clear, legible and relevant notes or zero) | 5 | ||
| Answered questions from assessor confidently demonstrating knowledge (Award 5 marks for clear and accurate answers or zero) | 5 | ||
| Sub-Total | 40 | ||
| PRODUCT CHECKLIST | |||
| Clarity and completeness of written notes on importance of irrigation and drainage (Award 5 marks for notes covering all key points clearly or zero) | 5 | ||
| Use of correct terminology and examples in oral explanation (Award 5 marks for correct terms and relevant examples or zero) | 5 | ||
| Sub-Total | 10 | ||
| GRAND TOTAL | 50 | ||
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