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

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

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

Bouwer-van Schilfgaarde

Glover-Dumm Equation

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.

= 178.74 hrs = 7 days 10.75 hrs

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

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

Falling with Accretion (Cooke)

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

Transient Nature of Water Table DRYING WT PROFILES WETTING WT PROFILES 20d 10d 4d 1d Simulated water table from HYDRUS 2D 100 cm 20d 20.02d 20.03d 20.07d 20.12d 20.14d 100 cm 2500 cm

Single Tile without Accretion (Cooke)

Single Tile with Accretion (Cooke)

Drain Sizing Tool

Materials

Drainage Coeff.

Drainage Coefficient

Design Criteria

Sedimentation Options

Design Chart

Can be Saved