Two reservoirs whose levels differ by $30\mathrm{.}5m$ are connected to a pipe $600mm$ diameter and $3050m$ long. The pipe crosses a ridge whose summit is $9\mathrm{.}1m$ above the level of the higher reservoir and at a distance of $305m$ along the pipe. Find the depth that a trench must be dug to lay the pipe in across the ridge if the pressure head in the pipe must not fall below $3m$ of water.

Calculate the flow rate in $\frac{m^3}{s}.$ Take $f=0\mathrm{.}0075,$ atmospheric pressure head $=10\mathrm{.}35m$ and neglect pipe entry and exit losses.

Answer: $5m,0\mathrm{.}56\frac{m^3}{s}$