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

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

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

Bubbling Tube Mariotte Bottle Soil Inner Cylinder Outer Cylinder

q EQUIVALENT K FOR VERTICAL FLOW D = D1 + D2 +...+Dn H1 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 + D2 +...+Dn

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

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

Hooghoudt Equation m 2r h de d S IMPERMEABLE LAYER

Hooghoudt Equation

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 = 0.007 m; hydraulic conductivity = 0.8 m/day. Estimate the required drain spacing

Kirkham Equation IMPERMEABLE LAYER h b d S 2r t

Kirkham Equation