$6$

A rectangular channel $6$m wide has a bed slope of $1$ in $1,200$ which for the likely maximum

flow has a normal depth of $1\mathrm{.}0$m$.$ Construction work downstream requires that a temporary

dam be built in the river which raises the depth immediately upstream of the dam to $1\mathrm{.}5$m$.$ The

Manning$$s n for the channel is estimated to be $0\mathrm{.}048.$ To assess the effects of this structure on

the regime upstream of the dam determine the following: $-$

$($i$)$ the flow in the stream

$[4$ marks$]$

$($ii$)$ how far upstream the depth will have reduced to $1\mathrm{.}4$m$.$