Subsurface Drainage (Tile) DesignThomas F. SchererNDSU Extension Agricultural EngineerThomas.Scherer@ndsu.edu(701) 231-7239

Tile Drainage Design Workshops2014Sioux Falls, SD - January 29-30Wahpeton, ND February 11-12Crookston, MN March 5-6Mankato, MN March 17-18

Where is Subsurface Drainage Used?Around the foundations of buildings with basements.Under roads and highways:To control heaving due to frost or water pressure, intercept side-hill water, reduce frost boils, etc.In the toe of earthen dams to control seepage water.Many other locations where subsurface water is a problem.On agricultural fields with high water table and/or salinity problems.

How Water Flows into Tile LinesRainWater Table Level in late July, August and September

How Water Flows into Tile LinesWater Table

How Water Flows into Tile LinesWater Table

How Water Flows into Tile LinesWater Table

How Water Flows into Tile LinesWater Table

Water Table No TileWater Table

Confining Layers Below Tile LinesWater Table

Confining Layers Below Tile LinesWater Table

Tiling Societal RequirementsVisit the County Natural Resource Conservation Service (NRCS) OfficeWetland Maps and LocationsLocal Water Resource Board (changes to drainage law)Permit required if tiling 80 acres or more.If the tile project is of statewide significance, then need approval from the State Water CommissionTalk to Neighboring Land OwnersFish and Wildlife Wetland Easements

Key Design ParametersA Successful Tile Project Starts with a Good PlanField CharacteristicsSurface drainageTopographySoilsDrainage CoefficientDrain OutletTile GradeSpacing between TileMains, Sub-Mains, Laterals

Field CharacteristicsTopographic MapAt least 1-foot vertical contours but 6-inch would be bestSoilsCheck county soil survey book or the NRCS web soil survey (http://websoilsurvey.nrcs.usda.gov)Take soil samples at the depth of drain tile (3 to 4 feet) to confirm soil survey infoSoils with sand fraction, do a sieve analysis to determine if filter (sock) is needed

Topographic Map 1 foot Contours98.0087.002600 ft.

Drainage CoefficientDesign amount of water to remove from the land in a 24 hour period (Maximum Flow)Field Crops With Good Surface Drainage to inchesHigh Value Crops (Vegetables, Potatoes, etc.)With Good Surface Drainage to inches inch per acre = 6,800 gallons (4.7 gpm)3/8 inch per acre = 10,210 gallons (7 gpm) inch per acre = 13,600 gallons (9.5 gpm)

Does removing 3/8th of an inch from the soil make much difference?Drained depth in soil is the difference between the volumetric water content at saturation (all pore spaces are full) and the soil water tension at air entry value (approximately 0.05 bar tension)For a silty clay soil, about 7 to 8 inchesFor a silty loam soil, about 5 to 6 inchesRemember: approximately 40% or the roots are in the top of the root zone

Gravity Flow Outlets

Need For Lift PumpNo Gravity OutletShallow ditch, No permission to make ditch deeperTile Mainline

Need For Lift PumpOutlet (ditch) fills up after a large rain and takes several days to subside (downstream control, small culvert, etc.)You want to have control of water leaving the field

Tile Spacing is Important

General Tile Spacing Recommendations(tile depth 3 to 4 feet)

Tile Spacing in feetSoil TypePermeabilityDC = DC= 3/8DC = Clay LoamVery Low6040 to 5035Silty Clay LoamLow7550 to 6045Silt LoamModerately Low9060 to 7060LoamModerate10070 to 8070Sandy LoamModerately High12080 to 12090

Drain Spacing Calculatorhttp://climate.sdstate.edu/water/DrainSpacingCal.html

Tile Line Spacing with Depth2 ft.3 ft.4 ft.28 ft.48 ft.62 ft.

Tile GradeRunRise RiseTile Grade = ------ RunTile Grade is usually expressed in percent gradeFor Example, 0.1 percent grade would be a 1 foot rise or drop in 1000 feet and a 0.5 percent grade would be a 5 foot rise or drop in 1000 feet

Tile Grade versus Full Carrying Capacity (gallons per minute)0.1 % slope = 1 foot vertical drop in 1000 feet of tile

Slope (%)Tile Diameter (inches)345810150.11123421502406000.21533592083407050.319417426041010300.52453953345301320

Tile Grade Can Change Along a LateralStarting and Stopping too Often Can Cause:Grade Control is Very Important!

Tile Installation PatternsTargeted Drainage Pattern

Possible Layout

Another Layout Option

200 acres Tiled 45 acres

160 acres

160 acres2440 feet

Basic Design ProcedureTopographical map of the field 1 foot vertical contoursField soil maps may need soil samples in areas indicative of major soil series at depth of tile (3 to 4 feet)NRCSs Websoil Survey (websoilsurvey.nrcs.usda.gov)Google Earth with soilweb.kmzIf sand is present have a soil sieve analysis done to determine sock/fine slot tile requirementSelect Outlet or Outlets select elevation of outletDesign the field layout (hardest part) Layout design in the field with colored flags or GPS instrumentsInstall in order: Outlet (gravity or pump station), then Mains, Submains and finally Laterals.

Controlled DrainageBaffles removed before planting and harvest to allow the field to drain.The outlet is raised after planting to potentially store water for crops.

160 acres2440 feet

160 acres

200 acres Tiled 45 acres

Thank you for your attention!

What is Subsurface Drainage?Slide courtesy of Dr. Gary Sand, University of Minnesota

Soil Water Holding CapacitySaturationOven DryField CapacityWilting PointPlant Available WaterDrainableWater

*****Controlled Drainage: water is held and released to control the amount of water retained.

Drainage water management is the practice of using a water control structure in a main, submain, or lateral to vary the depth of the drainage outlet. The water table must rise above the outlet depth for drainage to occur, as illustrated at right. The outlet depth, as determined by the control structure, is: Raised after harvest to limit drainage outflow and reduce the delivery of nitrate to ditches and streams during the off-season. Lowered in early spring and again in the fall so the drain can flow freely before field operations such as planting or harvest. Raised again after planting and spring field operations to create a potential to store water for the crop to use in midsummer.*