1. IRRIGATION PRINCIPLES
ERT 349 SOIL AND WATER ENGINEERING
IRRIGATION PRINCIPLES

2. Surface Irrigation

3. Surface Irrigation
Water flows across the soil surface to the point of infiltration
Oldest irrigation method and most widely used world-wide (90%) and in U.S. (60%)
Used primarily on agricultural or orchard crops

4. Types of Systems Water Flooding Basin
Relatively flat fields  allow water to find its own way across the surface
Minimal preparation and investment
Rather inefficient
Basin
Dikes used to surround an area and allow for water ponding (no runoff)
Basins are usually level

5. Water Flooding

6. Types of Systems, Contd…
Border
Strips of land with dikes on the sides
Usually graded but with no cross slope
Downstream end may be dike
Furrow
Small channels carry the water (entire surface is not wet)
Commonly used on row crops
Lateral as well as vertical infiltration
Furrows are usually graded

7. Border Irrigation
Border irrigation is the most common surface irrigation method for broadcast seeded crops. Level borders (basins) are used for lowland rice production in Arkansas and California, and throughout Asia.

8. Furrow Irrigation
Graded furrow irrigation is the most common type of surface irrigation in Oklahoma.

9. Furrow Irrigation
Most furrow irrigation in Oklahoma is supplied by ground water through gated pipes.

10. Water Supply Methods of water supply
Head ditch with siphon tubes or side-opening gates
Gated pipe (aluminum or plastic pipe with small gates that can be opened and closed)
Buried pipeline with periodically spaced valves at the surface

11. Siphon tubes
Siphon tubes supplying water from an open head ditch of the W.C. Austin Irrigation project near Altus, OK. The ditch is higher than the furrows of the field so gravity can carry water over the ditch bank.

12. Pipe gate
The pipe gates can be opened varying amounts to control the size of the furrow stream. Typical operating pressure on gated pipe systems is about 10 psi.

13. Furrow Irrigation
Runoff from furrows (tailwater) is one of the most significant inefficiencies in furrow irrigation. Deep percolation (especially near the head ditch) is the other.

14. Water Management Runoff recovery systems
Drainage ditches for collecting and conveying runoff to the reservoir
Reservoir for storing the runoff water
Inlet facilities to the reservoir (including desilting basin)
Pump and power unit
Conveyance system for transporting water (to same or different field)

15. A tailwater pit
A tailwater pit is a storage pond to collect furrow runoff for reapplication. It may be pumped back onto the same field with a low-head pump, or applied to another field.

16. Uniformity
Inherent non-uniformity because recession and advance curves are not parallel
Factors affecting
Inflow rate
Slope
Soil infiltration
Roughness
Channel shape
Inflow time
Length of run

17. Improving Irrigation Efficiency
Alternate furrow irrigation
Increases advance time, but reduces average infiltration depth (twice the width)
Cutback irrigation
Use large inflow rate during advance, and then reduce the inflow to match the soil's steady-state infiltration rate
Intensive management is required

18. Improving Irrigation Efficiency Cont’d
Land smoothing and laser grading
Helps to improve uniformity
Surge irrigation
Alternate on-off periods for applying water
Achieve higher efficiencies and uniformities in some soils
Lends itself to semi-automation

19. Land smoothing and grading
Laser controlled land forming equipment is used to shape uneven field surfaces into a smooth plane. Slopes of less than 0.1% (0.1 foot per 100 feet) are considered “level”. Slopes of over 0.1% are considered “graded”.

20. The rotating laser is placed at the field edge and set at the desired gradient and elevation. When the laser strikes the receiver on the earthmover, the machine cuts or fills soil at that location to give the “best fit plane” field surface.

21. Final smoothing with a land plane is required to achieve a useable field surface. Initially, 4-8 passes over the field will be needed (1-2 passes each in the N-S and E-W directions, and along each diagonal). Where significant fills were made, annual replaning will be needed to resmooth the surface until subsidence is reduced. Thereafter replaning may be needed only every 5-10 years, depending upon tillage methods.

22. Surge Irrigation
Surge irrigation is the application of water to the furrows in short pulses, with periods of no flow in between. The alternate wetting-up and drying-down cycles reduces the infiltration rate more rapidly and increases the advance of water across the field, resulting in a more uniform depth of infiltration from the head end to tail end of the field.