1. Surface Irrigation

2. 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

3. Types of Systems Water Spreading or Wild 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. Types of Systems, Contd…
Border
Strips of land with dikes on the sides
Usually graded but with no cross slope
Downstream end may be diked
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

6. 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.

7. Graded furrow irrigation is the most common type of surface irrigation in Oklahoma.

8. Most furrow irrigation in Oklahoma is supplied by ground water through gated pipes.

9. 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

10. Siphon tubes supplying water from an open head ditch of the W. C
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.

11. 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.

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

13. 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)

14. 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.

15. Surface Irrigation Hydraulics
Advance
Movement of water from the inlet end to the downstream end
Curve of Time vs. Distance is NOT linear
Rule-of-Thumb: 1/3 of the total advance time is needed to reach midpoint of the furrow length

16. Surface Irrigation Hydraulics , Cont’d
Recession
Process of water leaving the surface (through infiltration and/or runoff) after the inflow has been cut off
Usually begins to recede at the upstream end
Can also be plotted as Time vs. Distance
“Flatter" curve than the Advance Curve

17. Surface Irrigation Hydraulics, Cont’d
Infiltration
Opportunity Time: difference between Recession and Advance curves
Infiltration Depth: a function of the opportunity time and the infiltration class (rate) of the soil

18. Curve of Time Vs. Distance
Distance from inlet end (ft)

19. Opportunity Time

20. Infiltration vs. Opportunity Time

21. Infiltration Profile

22. 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

23. Efficiency Volume balance (or depth basis): dg = dz + ds + dr
Vg = Vz + Vs + Vr
g  gross
z  infiltration
s  surface storage
r  runoff
(or depth basis): dg = dz + ds + dr
Part of infiltration may go to deep percolation

24. Equations 10.3-10.5 for Calculating dg (Gross Application Depth)
Single furrow:
Furrow set:
Basin/border:

25. Example Problem

26. Example Problem Contd…

27. Other Design and Management Considerations
Maximum non-erosive stream size:
qmax = maximum non-erosive stream size (gpm)
S = field slope (%)
Set time and cutoff ratio:
CR = cutoff ratio
tL = advance time to the end of the field
tco = set time
Low CR's: rapid advance, good uniformity, high runoff
High CR's: slow advance, poor uniformity, low runoff

28. 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

29. 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

30. 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”.

31. 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.

32. 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.

33. 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.