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

2. Darcy’s Law h1 L h2
q: [L/T]
K: [L/T]
L, h: [L]

3. Water Air Bubbles Soil Bubbling tube Water inlet tubes Storage tube
Air at
atmospheric
pressure
Water level fixed
by bubbling tube
Outlet tube
Soil
Air seal plug
Outlet holes

4. Bubbling Tube
Mariotte Bottle
Soil
Inner Cylinder
Outer Cylinder

5. q EQUIVALENT K FOR VERTICAL FLOW D = D1 + D2 +...+DnH1 H2 H3 Hn
Hn+1 K1 K2 Kn D1 D2 Dn q
When flow is perpendicular to a series of soil layers, the flux through each layer is the same.
D = D1 + D Dn

6. 3 ft K = 3 ft/d
9 ft
Ke?
4 ft K = 2 ft/d
2 ft K = 4 ft/d

7. L EQUIVALENT K FOR HORIZONTAL FLOW Ha Hb
When flow is parallel to a series of soil layers, the discharge through unit thickness of the system is the sum of the discharges through the layers.. K1 D1 Q1 K2 D2 Q2 Kn Dn Qn

8. Hooghoudt Equation m 2r h de d S
IMPERMEABLE LAYER

9. Hooghoudt Equation

10. Estimating Spacing using The Hooghoudt Equation
i = Drainage Coefficient

12. For drainage design the following information is available:
depth of tile = 1.2 m; depth to water table = 0.8 m; depth to impermeable layer = 7.2 m; drainage coefficient = m; hydraulic conductivity = 0.8 m/day. Estimate the required drain spacing

13. Kirkham Equation
IMPERMEABLE LAYER h b d S 2r t

14. Kirkham Equation