$[$LETTER B$]$ The figure represents a $100m$ long waterproof curtain and the percolation network that describes

the movement of water on the ground. The downstream water level can vary between a

maximum elevation of $30\mathrm{.}0m$ and a minimum elevation of $22\mathrm{.}0m.$ To the soil take $=19k\frac{N}{m^3}$

and $k=10-6\frac{m}{s}.$

b$)$ Determine the effective vertical stress at point $Y,$ located at elevation $10\mathrm{.}0,$ assuming the water

level upstream at elevation $35\mathrm{.}0$ and the water level downstream at elevation $30\mathrm{.}0m.($Answer

$\{$:${}^{\text{'}}=101\mathrm{.}20k\frac{N}{m^2})$;