The Basicsof Agricultural Tile Drainage

1 The Basicsof Agricultural Tile DrainageBasic Engineering Principals 2 John Panuska PhD, PENatural Resources Extension SpecialistBiological Systems Engineering DepartmentUW MadisonASABE Tile Drain StandardsASAE EP480 MAR1998(R2008)Design of subsurface Drains in Humid ClimatesDesign StandardASABE Tile Drain StandardsConstruction StandardASAE EP481 FEB03 Construction of subsurface Drains in Humid AreasDrain Design if and where an adequate outlet can be installed! hydraulic conductivity (K) based on soil Drainage coefficient (Dc) based on crop and soil suitable depth for drains oTypical range 3 to 6 greater than ftoDepth / spacing balance to minimize spacingoUse soil textural table guidelinesoUse NRCS Web Design laterals and mains to accommodate the design flow.

2 Maintain minimum velocity to clean pipe.( ft / s -No silt; ft / sec -w/silt) Match pipe size to design flow.(telescoping the size of main) Properly design Design ProcedureDesign Challenges The design process results in a design for a 2 to 5 year event, controlling larger events too costly. Every soil will be different and crop type matters. Costs/benefits will vary from year to year. Climate trends are Tile Installation EquipmentTractor BackhoeTile PlowChain TrencherWheel TrencherDrain Tile MaterialsClay Tile (organic soils)Concrete Tile (mineral soils)Drain Pipe Materials-Polyethylene Plastic -Single wall corrugatedDual wall (smooth wall)Water enters the pipe through slots in wall I. The Drain Outlet MUST have sufficient grade for gravity flow !

3 < set preliminary grade>-If not, a pump station will benecessary. Receiving water must have adequate capacity. Provide guards to keep animals out. Daylight outlet pipe1 ft above base flow in receiving channelDrainage Pump StationsWhen you don t have the fall to use gravity ..II. Determine Ksatfor Soil Use web soil survey for site in question. Conduct site specific soil survey (test pit). Use values base on soil texture. Ask local experts (county staff, NRCS, Drainage contractors).III. Proper Lateral Depth and SpacingDrain spacing, water table depth and crop responseDrain depth and spacing integrate the water removal rate (Dc) and soil permeability(K)22122)4()8(LhKLhdKDC Hooghoudt Equation, 1940 Drain Depth / Spacing -EquationImage from Gary Sands U of MN DdmhDrain Spacing, Lconfining layerequivalent confining layersoil surfaceDdwater tabletile drainK1(in/day)K2(in/day)Flows horizontally toward drainsDRZD etermination of Soil K WSS can calculate a depth weighted K valueLateral Depth and SpacingSdThe goal is to maintain as consistent a Dc value across the field as Depth and Spacing A relationship exists between depth andspacing of drains.

4 For soils of uniform permeability, the deeperthe drains, the wider the spacing (within limits). Higher permeability soils can have greater spacing Need to provide adequate root depth above the saturated Depth and Spacing A relationship exists between depth andspacing of drains. For soils of uniform permeability, the deeperthe drains, the wider the spacing (within limits). Higher permeability soils can have greater spacing Need to provide adequate root depth above the saturated Depth and Spacing A relationship exists between depth andspacing of drains. For soils of uniform permeability, the deeperthe drains, the wider the spacing (within limits). Higher permeability soils can have greater spacing Need to provide adequate root depth above the saturated Depth and Spacing A relationship exists between depth andspacing of drains.

5 For soils of uniform permeability, the deeperthe drains, the wider the spacing (within limits). Higher permeability soils can have greater spacing Need to provide adequate root depth above the saturated Depth and SpacingVaries with soil permeability, crop and soil, kind of management practices crop, extent of surface drain depth range = 3 to 6 spacing = 30 to 100 / spacing balance to minimize cover greater than Gary Sands U of MNFlow Though Porous MediaP. GradientGravityDrain Depth / Spacing -TableVaries with soil permeability, crop and soil management practices, kind of crop, extent of surface (ft)Depth (ft)ClayClay LoamAverage LoamFine Sandy LoamSandy LoamPeat and MuckIrrigated Soils30 5039 6959 9898 12098 19798 295148 / Spacing - / Spacing -CalculatorPipe Capacity SideDesign Flow RateSideEngineering Design Aids -Tubing Drainage Chart -Flowinto LateralsArea drained = L x S; L = 1,500 ft; S = 61 ft; AT = (1,500 x 122) / 43,560 = ac; Dc = in.

6 Cubic feet / second = 63 gpmA2 Manning s equation for gravity pipe flow n = .009smooth interior to 8 to 12 .020> 12 Dc (in/day) x Area (ac) =Flow rate (ac in/day)(ac in/day) / rate (ft3/sec)From Gary Sands U of MNVI. Pipe Hydraulic CapacityPipe capacity (cfs) = D S 1/2nD = pipe diameter (ft) and S = pipe slope (ft/ft)Pipe CapacityPipe Capacity GraphRead pipe flow capacity for pipe size from the scale on the left. Water Volume Table----------------------------------- ----See your Drainage design in diameter pipe @ %= to cfs = 99 to 220 gpm------------------------------------- ---cfs x = : Drain SizeDetermine the diameter of corrugated plastic tubing and the slope needed to drain a ac area with a Drainage coefficient is Flow CapacityFor Dc = 3/4 in / dayArea = ac4 in pipe in pipe in pipe CapacityFlow RateRequires.

7 4 in diameter lineQ = cfsSlope range = %Velocity range = ft/secUse across different scales to telescope the pipe sizeDrainage Gary Sands U of MNDrainage Size and Grades Desirable minimum working grade is % Typical minimum pipe size is 3 -4 in humid regions and 5 -6 for organic soils. Minimum grade sufficient to maintain ft /sec ( ft / sec with sand and silt in flow).Pipe Size and Grades-Design Boundary Conditions - Very high velocities can cause sink holes when soil is actually pulled into the tile line. Blowouts can occur when lines become TextureMax. Velocity ft/secSand & sandy & silt clay & Clay sand or Watch out for steep-to-flat grade changes and overloading mains.

8 Blowouts !Tile Line BlowoutsTimeDuring storm eventAfter storm eventPhotos from: Eric Cooley, UW Discovery Farms Sub-surface Water Management Reduces the total water export. Annual nitrate load reductions ~ 15 to 75%. There are still a number of unknowns aboutperformance, research is on-going. Requires on-going : Drainage Water Management for the Midwest, Purdue Extension Service, System Cost-Approximate ! - Drainage system installation costs can vary significantlybased on terrain, soils, outlet availability, Range~ $800 -1,000 / acQUESTIONS ? ? ?