# 8.5 Problem Set

- Use the unit-gradient approach and Campbell’s hydraulic conductivity model (Eq. 4-7) to:
- estimate the drainage rate for a loam soil with
*K*= 310 mm d_{s}^{-1},*b*= 4.5, θ_{s}= 0.46, and θ = 0.40, and - estimate the volumetric water content at which the drainage rate would be 1 mm d
^{-1}.

- estimate the drainage rate for a loam soil with

- A uniform silt loam soil is initially wetted to θ = 0.42 cm
^{3}cm^{-3}to a depth of 1.2 m. The soil has a*K*value of 160 mm d_{s}^{-1}, θ_{s}= 0.44 cm^{3}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?

- What is the value of θ when the drainage rate drops to 1 mm d