Question

Hooghoudt's equation is used to design lateral drain spacing for two layered profiles, if

• A. Drains are located in the upper layer only
• B. Drains are located at the interface of the two layers only
• C. Drains are located in the lower layer only
• D. Drains are located either in the upper or lower layers only

Hint:

Placing the drains at the boundary interface of a two-layered soil profile allows the mathematical separation of hydraulic conductivity into $K_1$ (for horizontal flow above the drains) and $K_2$ (for radial flow below the drains) in Hooghoudt's equation.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Hooghoudt's equation is a steady-state formula used to determine the spacing between subsurface agricultural drains.
While originally developed for homogeneous soils, it can be mathematically adapted to two-layered soil profiles.
Detailed Explanation:
Let us review the boundary conditions of Hooghoudt's equation for a two-layered soil profile:
- A two-layered profile consists of an upper layer with hydraulic conductivity $K_1$ and a lower layer with hydraulic conductivity $K_2$.
- The standard derivation of Hooghoudt's equation for two-layered soils assumes that the drain pipes are located exactly at the interface of the two layers.
- This assumption simplifies the flow equations, splitting the flow into horizontal flow occurring purely in the upper layer (above the drains) and radial flow occurring in the lower layer (below the drains).

Step 2: Final Answer:
The drains must be located at the interface of the two layers, which corresponds to Option (B).