A rectangular channel is $2\mathrm{.}5$ m wide and conveys a discharge of $2\mathrm{.}75$ m$3$

$/$s at a depth

of $0\mathrm{.}90$ m$.$ A contraction of width is proposed at a section in this canal.

Calculate the water surface elevations in the contracted section as well as in an

upstream $2\mathrm{.}5$ m wide section when the width of the proposed contraction is

$($a$)2\mathrm{.}0$ m and

$($b$)1\mathrm{.}5$ m$.$

$($Neglect energy losses in the transition$).$