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

L h1h1 h2h2 Darcy’s Law q: [L/T]K: [L/T] L, h: [L]

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

Inner Cylinder Outer Cylinder Mariotte Bottle Bubbling Tube Soil

H1H1 H2H2 H3H3 HnHn H n+1 K1K1 K2K2 KnKn D1D1 D2D2 DnDn q EQUIVALENT K FOR VERTICAL FLOW When flow is perpendicular to a series of soil layers, the flux through each layer is the same. D = D 1 + D D n

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

Q2Q2 HbHb K1K1 K2K2 KnKn D1D1 D2D2 DnDn EQUIVALENT K FOR HORIZONTAL FLOW 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.. HaHa Q1Q1 QnQn L

IMPERMEABLE LAYER h m d S 2r Hooghoudt Equation dede

Estimating Spacing using The Hooghoudt Equation i = Drainage Coefficient

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

For drainage design the following information is available: depth of tile = 4 ft; depth to water table = 1 ft; depth to impermeable layer = 12 ft; drainage coefficient = 3/8 inches; hydraulic conductivity = 2 inch/hr. Estimate the required drain spacing 34 8

IMPERMEABLE LAYER h b d S 2r t Kirkham Equation