Question $3(20$ marks$)$:

Figure below shows the cross$-$section of a concrete gravity dam and reservoir resting on a $40$ m thickness layer of homogeneous and isotropic low$-$porosity $(n=5\%)$ sandy soil on impervious rock. The saturated hydraulic conductivity of the sandy soil $10\frac{m}{d}.$ The crest of the concrete gravity dam is approximately $20$ m long $($normal to the picture$).$

a$)(10$ marks$)$ Using a flow net analysis, calculate the volume of water that will seep beneath the dam through the sandy soil in a day day