2 Surface IrrigationWater flows across the soil surface to the point of infiltrationOldest 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 surfaceMinimal preparation and investmentRather inefficientBasinDikes used to surround an area and allow for water ponding (no runoff)Basins are usually level
5 Types of Systems, Contd… BorderStrips of land with dikes on the sidesUsually graded but with no cross slopeDownstream end may be dikedFurrowSmall channels carry the water (entire surface is not wet)Commonly used on row cropsLateral as well as vertical infiltrationFurrows 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 gatesGated 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 reservoirReservoir for storing the runoff waterInlet facilities to the reservoir (including desilting basin)Pump and power unitConveyance 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 AdvanceMovement of water from the inlet end to the downstream endCurve of Time vs. Distance is NOT linearRule-of-Thumb: 1/3 of the total advance time is needed to reach midpoint of the furrow length
16 Surface Irrigation Hydraulics , Cont’d RecessionProcess of water leaving the surface (through infiltration and/or runoff) after the inflow has been cut offUsually begins to recede at the upstream endCan also be plotted as Time vs. Distance“Flatter" curve than the Advance Curve
17 Surface Irrigation Hydraulics, Cont’d InfiltrationOpportunity Time: difference between Recession and Advance curvesInfiltration 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)
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 ratiotL = advance time to the end of the fieldtco = set timeLow CR's: rapid advance, good uniformity, high runoffHigh CR's: slow advance, poor uniformity, low runoff
28 Improving Irrigation Efficiency Alternate furrow irrigationIncreases advance time, but reduces average infiltration depth (twice the width)Cutback irrigationUse large inflow rate during advance, and then reduce the inflow to match the soil's steady-state infiltration rateIntensive management is required
29 Improving Irrigation Efficiency Cont’d Land smoothing and laser gradingHelps to improve uniformitySurge irrigationAlternate on-off periods for applying waterAchieve higher efficiencies and uniformities in some soilsLends 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.