surface irrigation. water flows across the soil surface to the point of infiltration oldest...

Surface IrrigationSurface Irrigation

Surface IrrigationSurface 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

Types of SystemsTypes of Systems• Water Spreading or Wild FloodingWater Spreading or Wild Flooding

– Relatively flat fields -- allow water to find its own way Relatively flat fields -- allow water to find its own way across the surfaceacross the surface

– Minimal preparation and investmentMinimal preparation and investment– Rather inefficientRather inefficient

• BasinBasin– Dikes used to surround an area and allow for water Dikes used to surround an area and allow for water

ponding (no runoff)ponding (no runoff)– Basins are usually levelBasins are usually level

Types of Systems, Types of Systems, Contd…Contd…

• BorderBorder– Strips of land with dikes on the sidesStrips of land with dikes on the sides– Usually graded but with no cross slopeUsually graded but with no cross slope– Downstream end may be dikedDownstream end may be diked

• FurrowFurrow– Small channels carry the water (entire surface is not wet)Small channels carry the water (entire surface is not wet)– Commonly used on row cropsCommonly used on row crops– Lateral as well as vertical infiltrationLateral as well as vertical infiltration– Furrows are usually gradedFurrows are usually graded

Water SupplyWater Supply

• Methods of water supplyMethods of water supply– Head ditch with siphon tubes or side-opening gatesHead ditch with siphon tubes or side-opening gates– Gated pipe (aluminum or plastic pipe with small Gated pipe (aluminum or plastic pipe with small

gates that can be opened and closed)gates that can be opened and closed)– Buried pipeline with periodically spaced valves at Buried pipeline with periodically spaced valves at

the surfacethe surface

Water ManagementWater Management

• Runoff recovery systemsRunoff recovery systems– Drainage ditches for collecting and conveying Drainage ditches for collecting and conveying

runoff to the reservoirrunoff to the reservoir– Reservoir for storing the runoff waterReservoir for storing the runoff water– Inlet facilities to the reservoir (including desilting Inlet facilities to the reservoir (including desilting

basin)basin)– Pump and power unitPump and power unit– Conveyance system for transporting water (to Conveyance system for transporting water (to

same or different field)same or different field)

Surface Irrigation HydraulicsSurface Irrigation Hydraulics

• AdvanceAdvance– Movement of water from the inlet end to the Movement of water from the inlet end to the

downstream enddownstream end– Curve of Time vs. Distance is NOT linear Curve of Time vs. Distance is NOT linear – Rule-of-Thumb: 1/3 of the total advance time is Rule-of-Thumb: 1/3 of the total advance time is

needed to reach midpoint of the furrow lengthneeded to reach midpoint of the furrow length

Surface Irrigation Hydraulics , Surface Irrigation Hydraulics , Cont’dCont’d

• RecessionRecession– Process of water leaving the surface (through Process of water leaving the surface (through

infiltration and/or runoff) after the inflow has been infiltration and/or runoff) after the inflow has been cut offcut off

– Usually begins to recede at the upstream endUsually begins to recede at the upstream end– Can also be plotted as Time vs. Distance Can also be plotted as Time vs. Distance – ““Flatter" curve than the Advance CurveFlatter" curve than the Advance Curve

Surface Irrigation Hydraulics, Surface Irrigation Hydraulics, Cont’dCont’d

• InfiltrationInfiltration– Opportunity Time: difference between Recession Opportunity Time: difference between Recession

and Advance curves and Advance curves – Infiltration Depth: a function of the opportunity Infiltration Depth: a function of the opportunity

time and the infiltration class (rate) of the soiltime and the infiltration class (rate) of the soil

Curve of Time Vs. DistanceCurve of Time Vs. Distance

Distance from inlet end (ft)

Opportunity TimeOpportunity Time

Infiltration vs. Opportunity TimeInfiltration vs. Opportunity Time

Infiltration ProfileInfiltration Profile

UniformityUniformity

• Inherent non-uniformity because recession and Inherent non-uniformity because recession and advance curves are not parallel advance curves are not parallel

• Factors affectingFactors affecting– Inflow rateInflow rate– SlopeSlope– Soil infiltrationSoil infiltration– RoughnessRoughness– Channel shapeChannel shape– Inflow timeInflow time– Length of runLength of run

EfficiencyEfficiency

• Volume balanceVolume balance– VVgg = V = Vzz + V + Vss + V + Vrr

– g g gross gross– z z infiltration infiltration– s s surface storage surface storage– r r runoff runoff

• (or depth basis): d(or depth basis): dgg = d = dzz + d + dss + d + drr

• Part of infiltration may go to deep percolationPart of infiltration may go to deep percolation

Equations 10.3-10.5 for Calculating dEquations 10.3-10.5 for Calculating dgg

(Gross Application Depth)(Gross Application Depth)

• Single furrow:Single furrow:

• Furrow set:Furrow set:

• Basin/border:Basin/border:

dq t

WLgs co

1155

dQt

NWLgco

1155

dQt

W Lgco

b b

96 3.

Example ProblemExample Problem

Example Problem Contd…Example Problem Contd…

Other Design and Management Other Design and Management ConsiderationsConsiderations

• Maximum non-erosive stream size:Maximum non-erosive stream size:

– qqmaxmax = maximum non-erosive stream size (gpm) = maximum non-erosive stream size (gpm)– S = field slope (%)S = field slope (%)

• Set time and cutoff ratio:Set time and cutoff ratio:

– CR = cutoff ratioCR = cutoff ratio– ttLL = advance time to the end of the field = advance time to the end of the field– ttcoco = set time = set time– Low CR's: rapid advance, good uniformity, high runoffLow CR's: rapid advance, good uniformity, high runoff– High CR's: slow advance, poor uniformity, low runoffHigh CR's: slow advance, poor uniformity, low runoff

Sq

10max

CRt

tL

co

Improving Irrigation Improving Irrigation EfficiencyEfficiency

• Alternate furrow irrigationAlternate furrow irrigation– Increases advance time, but reduces average Increases advance time, but reduces average

infiltration depth (twice the width)infiltration depth (twice the width)

• Cutback irrigationCutback irrigation– Use large inflow rate during advance, and then reduce Use large inflow rate during advance, and then reduce

the inflow to match the soil's steady-state infiltration the inflow to match the soil's steady-state infiltration raterate

– Intensive management is requiredIntensive management is required

Improving Irrigation Efficiency Improving Irrigation Efficiency Cont’dCont’d

• Land smoothing and laser gradingLand smoothing and laser grading– Helps to improve uniformityHelps to improve uniformity

• Surge irrigationSurge irrigation– Alternate on-off periods for applying waterAlternate on-off periods for applying water– Achieve higher efficiencies and uniformities in some Achieve higher efficiencies and uniformities in some

soilssoils– Lends itself to semi-automationLends itself to semi-automation