4) A wastewater sewer having a slope of 0.001 and a diameter of 1000 mm is carrying a maximum flow of \( 450 \mathrm{~L} / \mathrm{sec} \). Another sewer which is carrying a maximum flow of \( 85 \mathrm{~L} / \mathrm{sec} \) and having a slope of 0.002 and a diameter of 500 mm will be attached to the first one. What should be the h/D ratio of the sewers at the manhole if the sewage is not wanted to go back in the smaller diameter sewer? (Hint: water depth of the sewers will be equal in each sewer and consider the rules-of-thumb to compensate for non-uniform flow occurring at sewer junctions)