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Drainage System Design and Layout

Drainage System Design and Layout. Design Process Flowchart. Select DC, Spacing & Depth. Background Information (Soils, Topo, Crops). Determine Drain Sizes. Installation. Drainage Needed. Develop System Layout. NO. Confirm Outlet. Determine Grades & Depth. NO.

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Drainage System Design and Layout

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  1. Drainage System Design and Layout

  2. Design Process Flowchart Select DC, Spacing & Depth Background Information (Soils, Topo, Crops) Determine Drain Sizes Installation Drainage Needed Develop System Layout NO Confirm Outlet Determine Grades & Depth NO

  3. Design Process Flowchart Select DC, Spacing & Depth Background Information (Soils, Topo, Crops) Determine Drain Sizes Installation Drainage Needed Develop System Layout NO Confirm Outlet Determine Grades & Depth NO

  4. Drainage Outlets

  5. Design Curves Outlet channels designed according to Curve B will provide excellent agricultural drainage in Illinois. Use this curve for drainage of truck crops, nursery crops, and other specialty crops. Designs based on curve B will provide the best drainage that can normally be justified in agricultural areas.

  6. Design Curves Channels that are designed according to curve C will provide good agricultural drainage in Illinois. This curve is the one most often recommended for drainage of Illinois cropland

  7. Drainage Outlets Designs based on curve D provide satisfactory agricultural drainage as long as frequent overflow does not cause excessive damage. This curve is generally recommended for pasture or woodland. It may also be adequate for drainage of general cropland in northern Illinois, provided that the landowner carries out an excellent maintenance program. Designs based on curve D provide the minimum amount of drainage recommended in Illinois.

  8. Design Curves Drainage CFS/ Acre In/Day Curve 100 Acres (Drainage Coefficient) B 20 4.8 C 8 2.0 D 5 1.2 For comparison: For a 100 acre watershed, RCN = 75, Avg. Slope = 1% in Central Illinois A 2 Yr., 24 Hr. Rainfall yields 1” of Runoff and would result in a Peak Flow of 30 CFS. A 10 Yr., 24 Hr. Rainfall yields 2” of Runoff and would result in a Peak Flow of 70 CFS.

  9. Ditch Configuration Once you know what the capacity of the outlet channel must be, you need to determine the size that will enable it to convey the desired amount of flow without letting the water surface rise above a predetermined elevation. The following sections describe some basic hydraulic concepts that will help you design a channel of the proper size .

  10. Maximum Velocity Soil Texture (ft/sec) Sand or sandy loam 2.5 Silt loam 3.0 Sandy clay loam 3.5 Clay loam 4.0 Clay or silty clay 5.0 Fine gravel, cobbles, or 5.0 graded loam to cobbles Graded mixture silt to cobbles 5.5 Coarse gravel, shales, 6.0 or hardpans Outlet Ditches Velocity The velocity of water flow must be high enough to prevent siltation in the channel but low enough to avoid erosion. Listed on the next page are the maximum velocities for drainage areas of 640 acres or less. The velocity should be no lower than 1.5 feet per second. A lower velocity will cause siltation, which encourages moss and weed growth and reduces the cross section of the channel.

  11. Hydraulic Gradeline

  12. Channel Velocity The most widely used equation for designing outlet channels was developed by Robert Manning in 1890 and is known as Manning's equation: where V = average velocity of flow (ft/sec), n = coefficient of roughness, R = hydraulic radius (ft), s = slope of hydraulic gradient (ft/ft).

  13. Manning Routine

  14. Design Process Flowchart Select DC, Spacing & Depth Background Information (Soils, Topo, Crops) Determine Drain Sizes Installation Drainage Needed Develop System Layout NO Confirm Outlet Determine Grades & Depth NO

  15. Drainage Coefficient

  16. Design Process Flowchart Select DC, Spacing & Depth Background Information (Soils, Topo, Crops) Determine Drain Sizes Installation Drainage Needed Develop System Layout NO Confirm Outlet Determine Grades & Depth NO

  17. Drain Spacing & Depth • Design for uniform depth throughout system • (depends on layout) • Depth will of course vary on flat and rolling topography

  18. System Layout

  19. System Layout

  20. System Layout

  21. Contour Map

  22. System Layout Cost Differential: $50/acre

  23. Design Process Flowchart Select DC, Spacing & Depth Background Information (Soils, Topo, Crops) Determine Drain Sizes Installation Drainage Needed Develop System Layout NO Confirm Outlet Determine Grades & Depth NO

  24. Drain Sizing Tool

  25. Result Display

  26. Materials

  27. Drainage Materials

  28. Drainage Materials

  29. Drainage Coeff.

  30. Drainage Coefficient

  31. Design Criteria

  32. Tile Mathematics 10 = 3 x 6 12/2 = 8

  33. Sedimentation Options

  34. Design Chart

  35. Can be Saved

  36. Lateral Specification

  37. Lateral Specification

  38. Inlets

  39. Questions?

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