Tile drains have to be installed in an agricultural land having soil permeability of $2.3 \times 10^{-3} \mathrm{~mm} \mathrm{~s}^{-1}$. An impermeable stratum exists at $3.2 \mathrm{~m}$ below the land surface, and it is desired to keep the water level at least $1.0 \mathrm{~m}$ below the land surface. The average discharge of the drainage system is $2.0 \mathrm{~mm}$ day $^{-1}$. If the tile drains are planned to be placed at $1.5 \mathrm{~m}$ below the land surface, the drain spacing in $\mathrm{m}$, assuming the equivalent depth to be the same as the tile depth, is
(A) 10.6
(B) 12.4
(C) 13.9
(D) 19.7
Tile drains have to be installed in an agricultural land having soil permeability of $2.3 \times 10^{-3} \mathrm{~mm} \mathrm{~s}^{-1}$. An impermeable stratum exists at $3.2 \mathrm{~m}$ below the land surface, and it is desired to keep the water level at least $1.0 \mathrm{~m}$ below the land surface. The average discharge of the drainage system is $2.0 \mathrm{~mm}$ day $^{-1}$. If the tile drains are planned to be placed at $1.5 \mathrm{~m}$ below the land surface, the drain spacing in $\mathrm{m}$, assuming the equivalent depth to be the same as the tile depth, is
(A) 10.6
(B) 12.4
(C) 13.9
(D) 19.7