Subsurface Drainage (Tile) Design Thomas F. Scherer NDSU Extension Agricultural Engineer (701)

Tile Drainage Design Workshops 2014  Sioux Falls, SD - January  Wahpeton, ND – February  Crookston, MN – March 5-6  Mankato, 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 Lines Runoff Rain Water Table Level in late July, August and September

How Water Flows into Tile Lines Water Table Runoff

How Water Flows into Tile Lines Water Table Runoff

How Water Flows into Tile Lines Water Table Runoff

How Water Flows into Tile Lines Water Table

Water Table – No Tile Water Table Runoff

Confining Layers Below Tile Lines Water Table

Confining Layers Below Tile Lines Water Table

Tiling Societal Requirements  Visit the County Natural Resource Conservation Service (NRCS) Office  Wetland Maps and Locations  Local 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 Commission  Talk to Neighboring Land Owners  Fish and Wildlife Wetland Easements

Key Design Parameters  A Successful Tile Project Starts with a Good Plan  Field Characteristics Surface drainage Topography Soils  Drainage Coefficient  Drain Outlet  Tile Grade  Spacing between Tile  Mains, Sub-Mains, Laterals

Field Characteristics  Topographic Map  At least 1-foot vertical contours but 6-inch would be best  Soils  Check county soil survey book or the NRCS web soil survey ( ) Take soil samples at the depth of drain tile (3 to 4 feet) to confirm soil survey info Soils with sand fraction, do a sieve analysis to determine if filter (sock) is needed

Topographic Map – 1 foot Contours ft.

Drainage Coefficient  Design amount of water to remove from the land in a 24 hour period (Maximum Flow)  Field Crops With Good Surface Drainage – ¼ to ½ inches  High Value Crops (Vegetables, Potatoes, etc.) With Good Surface Drainage – ½ to ¾ inches  ¼ inch per acre = 6,800 gallons (4.7 gpm)  3/8 inch per acre = 10,210 gallons (7 gpm)  ½ inch per acre = 13,600 gallons (9.5 gpm)

Does removing 3/8 th 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 inches  For a silty loam soil, about 5 to 6 inches  Remember: approximately 40% or the roots are in the top ¼ of the root zone

Gravity Flow Outlets

Need For Lift Pump  No Gravity Outlet  Shallow ditch, No permission to make ditch deeper Tile Mainline

Need For Lift Pump  Outlet (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 feet Soil TypePermeabilityDC = ¼”DC= 3/8”DC = ½” Clay LoamVery Low 6040 to 5035 Silty Clay LoamLow 7550 to 6045 Silt LoamModerately Low 9060 to 7060 LoamModerate to 8070 Sandy LoamModerately High to 12090

Drain Spacing Calculator

Tile Line Spacing with Depth 2 ft. 3 ft. 4 ft. 28 ft. 48 ft. 62 ft.

Tile Grade Run Rise Tile Grade = Run Tile Grade is usually expressed in percent grade For 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) Slope (%) Tile Diameter (inches) % slope = 1 foot vertical drop in 1000 feet of tile

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

Tile Installation Patterns Targeted Drainage Pattern

Possible Layout

Another Layout Option

200 acres Tiled 45 acres

160 acres

2440 feet

Basic Design Procedure  Topographical map of the field 1 foot vertical contours  Field soil maps – may need soil samples in areas indicative of major soil series at depth of tile (3 to 4 feet)  NRCS’s Websoil Survey (websoilsurvey.nrcs.usda.gov)  Google Earth – with soilweb.kmz  If sand is present – have a soil sieve analysis done to determine sock/fine slot tile requirement  Select Outlet or Outlets – select elevation of outlet  Design the field layout (hardest part)  Layout design in the field with colored flags or GPS instruments  Install in order: Outlet (gravity or pump station), then Mains, Submains and finally Laterals.

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

160 acres 2440 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 Capacity Saturation Oven Dry Field Capacity Wilting Point Plant Available Water Drainable Water