A rectangular cast iron pipe having two sides of $0\mathrm{.}2m$ and $0\mathrm{.}125m$ and a $305m$ length is used to drain water. The available head is $4\mathrm{.}57m$ of water. Neglecting any losses in fitting and joints in the pipe, please calculate the flow rate. $($As a first trial, assume that $v=1\mathrm{.}7\frac{m}{s})$