$7\mathrm{.}41.$ A sharp$-$crested weir is to be placed $100m$ downstream

of a water park on a river such that the river stage at the

park is $5\mathrm{.}50m$ when the flow rate in the river is $25\frac{m^3}{s}.$

The longitudinal slope of the river is $0\mathrm{.}1\%,$ the elevation

of the bottom of the river at the park location is $2\mathrm{.}00m,$

the side slopes are $2$:$1($H:V$),$ and the bottom width is

$6\mathrm{.}00m.$ It can be assumed that the Manning's $n$ of the

river is $0\mathrm{.}05.$ Specify a crest length and elevation of the

weir crest that will have the desired effect.