$4.$ A rectangular sedimentation tank is to be designed for a flow of $20$ million liter per day using a $2$:$1$ length$-$width ratio and overflow rate of $\backslash (24\backslash$mathrm$\{$~m$\}^\{3\}/\backslash$mathrm$\{$m$\}^\{2\}\backslash ).$day. The tank is to be $2$ m deep. Determine the dimensions for the tank and the detention time.

NOTE: Make the necessary assumptions or use accompanying coefficients for each question by citing the relevant reference.