Question

The spacing of tile drains to relieve water-logged land is directly proportional to

• A. Depth of drain below the ground surface
• B. Depth of impervious strata from the drain
• C. Depth of drain below the water level
• D. Coefficient of permeability of the soil to be drained

Hint:

For tile drainage systems, \[ \boxed{\text{Higher permeability } \Rightarrow \text{Larger drain spacing}} \] whereas low permeability soils require closely spaced drains.

Answer 1

The Correct Option is D

Concept: Tile drains are installed to remove excess water from agricultural lands and lower the groundwater table. The spacing between tile drains depends upon several factors such as soil permeability, drain depth, and recharge rate. According to drainage theory, the spacing between tile drains is directly proportional to the coefficient of permeability of the soil. Higher permeability allows water to move more easily through the soil, permitting larger drain spacing.

Step 1: Identify the governing parameter. The coefficient of permeability (\(k\)) determines the ease with which water flows through the soil. A larger value of \(k\) means water reaches the drains more quickly.

Step 2: Determine the effect on drain spacing. Since water moves faster in highly permeable soils, \[ \boxed{\text{Drain spacing increases with the coefficient of permeability}.} \] Hence, the spacing of tile drains is directly proportional to the permeability of the soil. Therefore, the correct option is \[ \boxed{(D)\;\text{Coefficient of permeability of the soil to be drained}.} \]