The statement which is not correct for the porous medium is
GATE AG - 2023,
Answer: D
The incorrect statement is Darcy's velocity in unsaturated soil is always greater than that in saturated soil.
Hydraulic conductivity is highest when the pores are full of water. As a soil dries, water flows only through the smaller, still-filled pores and along thinner films, so conductivity, and with it Darcy's velocity under a given gradient, falls steeply. Flow in unsaturated soil is therefore normally slower, not faster.
The other statements are correct. Seepage velocity is Darcy's velocity divided by porosity, and porosity is less than 1, so it is always greater. Darcy's velocity depends on hydraulic conductivity and gradient, not on porosity alone. Ponding water on the surface raises the hydraulic head and so the gradient driving flow, which increases the seepage velocity.
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