$2.$ Rectangular pre$-$sedimentation tanks to be used to remove grit and sand from river water that is used to produce $\backslash (20000\backslash$mathrm$\{$~m$\}^\{3\}/\backslash$mathrm$\{$d$\}\backslash )$ drinking water. Use an overflow rate of $\backslash (20\backslash$mathrm$\{$~m$\}^\{3\}\backslash$cdot $\backslash$mathrm$\{$~m$\}^\{2\}/\backslash$mathrm$\{$d$\}\backslash )$ and a weir loading rate of $\backslash (200\backslash$mathrm$\{$~m$\}^\{3\}/\backslash$mathrm$\{$m$\}.\backslash$mathrm$\{$d$\}\backslash ),$ a detention time of $3$ hrs $.$ A minimum of two tanks are to be used. Find the following:

a$.$ The surface area of the tank.

b$.$ Tank dimensions $(\backslash (\backslash$mathrm$\{$L$\}^\{*\}\backslash$mathrm$\{$~W$\}^\{*\}\backslash$mathrm$\{$H$\}\backslash )),$ use width to length ratio of $4$:$1,$ Maximum length $40$ m $,$

c$.$ Find the required weir length and propose a weir arrangement $($such as finger type weirs$)$ showing dimensions and way of arrangement.

d$.$ what is the horizontal velocity in the tank?

e$.$ Draw a horizontal plan for the sedimentation tank showing the effluent weir arrangement and draw a longitudinal vertical cross section showing all dimensions. The drawing should be a sketch only; you don't need to draw to scale.