Final answer:
The depth of the impermeable barrier below the drains is larger when there is a higher pressure exerted on the barrier.
Step-by-step explanation:
The depth of the impermeable barrier below the drains is larger when there is a higher pressure exerted on the barrier. This can occur when there is a larger volume of water above the barrier or when the water is deeper below the surface. The depth of the impermeable barrier is directly related to the pressure exerted on it.