A$.$ A storm sewer system is to be designed using the given on the image. Determine the required pipe diameters for the dis$-$

charge based on a $2-$year return period rainfall. Use concrete pipe ma$-$

terial $(n=0\mathrm{.}014).$ Commercial pipe sizes should be rounded up to the

nearest $25$ mm $.$

B$.$ Assess the limitation of using the rational formula for hydraulic system design analysis. Explain why it remains to be widely used for urban drainage system design, in spite of such restriction.

C$.$ Why is there a need to determine various times of concentration in the drainage system design of an area using rational formula? Explain your answer in relation to the concept of the rational method and rainfall$-$runoff relationship.

D$.$ Why do you think is drainage flooding prevalent in the Philippines? Discuss the rainfall$-$runoff factors that contribute to such perennial problem in the country.