A rectangular channel $1\mathrm{.}2$ m wide has at its end a rectangular sharp$-$edged notch with an effective width after allowing for side contractions of $0\mathrm{.}85$ m and with its sill $0\mathrm{.}2$ m from the bottom of the channel. Assuming that the velocity head averaged over the channel is V$2/2$g where V is the mean velocity and $=1\mathrm{.}1,$ calculate the discharge in cubic metres per second when the head is $250$ mm above the sill allowing for the velocity of approach.