Irrigation Structures and Methods in Agricultural Campuses
Irrigation Structures in Agricultural Campuses
Efficient Water Management
Efficient water management is crucial in agriculture and can only be achieved with adequate infrastructure to control water flow. Farmers often face the challenge of getting water to their property efficiently. This involves using various structures, some of which are permanent and others portable or temporary.
Diversion and Conveyance Structures
These structures are built at the head of a channel or river. Channels are classified into main, bypass, and distribution channels. Water is often derived from a primary source or a gate framework using bars to raise the water level.
Types of Diversion Structures:
- Metal Trance: Placed in slightly sandy soil.
- Hill Retention: A light, easy, and cost-effective method using a drain hose to divert a portion of the stream.
- Sluice Boxes: Wooden boxes used for row crops, allowing water to flow through a side channel to a header ditch or berm.
Water Conduction in the Campus
Irrigation water is typically conveyed through channels or pipes. The most common type is unlined earthen channels, which offer low cost but have disadvantages like easy filtration, low speed, and weed growth.
Structures for Water Conduction:
- Bridges and Viaducts: Used to cross depressions when channels are elevated.
- Tunnels: Reduce the length of a channel when traversing mountains or hills.
- Falls and Water Breaks: Built to slow down water flow on steep slopes.
- Inverted Siphons: Used to cross roads or canals where a change in elevation is difficult.
Structures and Devices for Measuring Irrigation Water
With increasing population and intensive agriculture, accurate water measurement is essential. Measurement units include specific volume and flow rate, expressed in liters or cubic meters.
Measuring Devices:
- Standard Open Channel: Includes weirs, flumes, and Parshall flumes. Economical for low to moderate flow rates.
- Non-Standard: Any shape can be used as a meter once calibrated.
Types of Weirs:
- Sharp-Crested Rectangular Weir: Rectangular notch placed at the bottom of a reservoir.
- Trapezoidal or Cipolletti Weir: Similar to rectangular weirs but with a trapezoidal shape.
- Triangular Weir: V-shaped notch for accurate measurement.
Selection of Weirs
Rectangular and triangular weirs are generally the most effective.
Furrow and Melgar Irrigation
Furrow Irrigation
This method wets only the root layer through water infiltration. Moisture advances along the furrows.
Meters for Furrow Equalization:
These meters work best when adapted to row crops and various soil types.
Shape, Dimensions, and Separation of Furrows:
These factors depend on the implement used and the soil type.
Furrow Length:
To reduce percolation losses, either increase the flow rate or reduce the furrow length.
Furrow Design:
Design considerations include length, soil type, and field testing methods.
Melgar Irrigation
Water flows over the surface in thin sheets, wetting the entire terrain. The field is divided into strips bordered by ridges.
Conditions for Melgar Irrigation:
- Suitable for high-density crops.
- Requires flat terrain with good leveling.
Melgar Width:
Determined by topography, slope, water flow, and agricultural implements.
Melgar Length:
Depends on soil texture, slope, and flow rate.
Melgar Design:
Relates length, width, and slope for optimal irrigation.
Sprinkler Irrigation
Water is applied as a mist using a mechanized system.
Conditions for Sprinkler Irrigation:
- Suitable for irregular terrain, shallow soils, and high infiltration rates.
Disadvantages of Sprinkler Irrigation:
- High cost.
- Susceptibility to wind distortion.
Components of a Sprinkler System:
- Sprinkler
- Water pump equipment
- Pipes
- Sprinklers or nozzles
- Accessories
Types of Sprinklers:
- Low-Pressure Sprinklers: 1-2 atm
- Intermediate-Pressure Sprinklers: 2-4 atm
- High-Pressure Sprinklers: 4-7 atm
Drip Irrigation
Water is applied directly to the soil through emitters.
Components of a Drip Irrigation System:
- Lateral lines
- Distribution lines
- Main lines
- Control head
Components of a Typical Control Head:
- Valve connection to the water network
- Positive displacement meter
- Single output valve
- Fertilizer tank
- Vacuum relief valve
- Differential pressure gauge
- Main pressure control valve
- Fertilizer input to the system
- Primary water line filter
- Fertilizer runoff
- Fertilizer tank washing valve