Transient Drainage

1. Transient Drainage Department of Agricultural and Biological Engineering University of Illinois at Urbana-Champaign

2. de Falling Water Table m0 m 2r h S d IMPERMEABLE LAYER

3. dA = p(m-dm)S/2-pmS/2 = -pdmS/2 m-dm m 2r h S d IMPERMEABLE LAYER

4. Bouwer-van Schilfgaarde

5. Glover-Dumm Equation

6. A controlled drainage system is installed in a soil having a drainable porosity of 0.066, a hydraulic conductivity of 0.12 ft/hr and an impervious layer 12 ft below the drains. The drains are installed 4 ft below the soil surface and spaced 120 ft apart. If the water table is initially held at the soil surface, determine the time when the controlled structure should be opened to allow the mid-plane water table to be 3 ft below the soil surface at 6 am on April 28 when the farmer begins planting. Assume that the water table shaped like a fourth degree parabola and that no rain falls over the period when the water table is falling.

8. = 178.74 hrs = 7 days 10.75 hrs

9. de Falling Water Table with Accretion R m0 m 2r h S d IMPERMEABLE LAYER

10. Falling with Accretion (DeZeeuw-Hellinga) No contribution from above tile

11. Falling with Accretion (Cooke)

12. N m q x 2r o h o S N m q h x h(x) L 2r o h o x L(t)

13. 20d10d 4d 1d DRYING WT PROFILES WETTING WT PROFILES Transient Nature of Water Table Simulated water table from HYDRUS 2D 100 cm 20d20.02d20.03d20.07d20.12d20.14d 100 cm 2500 cm

15. Single Tile without Accretion (Cooke)

16. Single Tile with Accretion (Cooke)

17. Drain Sizing Tool

18. Materials

19. Drainage Coeff.

20. Drainage Coefficient

21. Design Criteria

22. Sedimentation Options

23. Design Chart

24. Can be Saved