There is a dam with an overflow spillway.$$ The maximum anticipated discharge is $30$ m$3/$s$/$m and the spillway crest is $60$m above the downstream sand river bed, which has a slope of $0\mathrm{.}002$ and n $=0\mathrm{.}018.$

$$

Find:$($a$)$ Elevation and length of stilling basin floor,

$($b$)$ If cavitation occurs,

$($c$)$ Scour depth downstream of the stilling basin,

$($d$)$ Method of deciding if the depth of scour found in Part $($c$)$ is acceptable or not?

$($e$)$ Action to take if the scour was too deep?

ensure to determine the design head cd in order to find H$.$ state whether the channel is stable by comparing with shields