A bridge is supported by elliptical piers having a width $1\mathrm{.}75m(5\mathrm{.}7ft)$ and a spacing of $12m(39\mathrm{.}4ft.$ The piers have a drag coefficient of $2\mathrm{.}0.$ If the downstream depth and velocity are $1\mathrm{.}90m(6\mathrm{.}23ft)$ and $2\mathrm{.}4\frac{m}{s}(7\mathrm{.}87f\frac{t}{s}),$ respectively, what is the backwater caused by the piers? $(20$ points$)$