Use the unit-gradient approach and Campbell’s hydraulic conductivity model (Eq. 4-7) to:
estimate the drainage rate for a loam soil with Ks = 310 mm d-1, b = 4.5, θs = 0.46, and θ = 0.40, and
estimate the volumetric water content at which the drainage rate would be 1 mm d-1.
A uniform silt loam soil is initially wetted to θ = 0.42 cm3 cm-3 to a depth of 1.2 m. The soil has a Ks value of 160 mm d-1, θs = 0.44 cm3 cm-3, and b = 4.7 in the Campbell hydraulic conductivity model.
What is the value of θ when the drainage rate drops to 1 mm d-1, assuming unit-gradient conditions?
How many mm of water have drained from the soil profile when that value of θ is reached?