$8\mathrm{.}11)$ Water flows through a rectangular channel $2\mathrm{.}0$ m wide at a flow rate of $\backslash (12\mathrm{.}0\backslash$mathrm$\{$~m$\}^\{3\}/\backslash$mathrm$\{$s$\}\backslash ).$ A submerged obstruction $0\mathrm{.}40$ m high is placed across the channel floor. Assuming frictionless flow, determine the increase or decrease in water level if the original depth before the obstruction is $3\mathrm{.}0$ m $.$