Question $5.$ Storm sewer design. $(25$ marks$)$

$($a$)$

A storm sewer system was designed for a town in Southem Ontario. The original design was based ou

a storm frequency of once in $10$ years. The rainfall intensity equation for this case is:

$i-2,\frac{820}{t+16},$ where $iisinm\frac{m}{h}$ and $tisin$ min.

The watershed had an average slope of $2\%,$ and the distance of the farthest point of the watershed to

the storm sewer inlet was $183$ m $.$ When the system was built, roof drains from the houses were fed

into the storm sewer, as did the runoff from the highways, so the watershed could be considered as

partly bare soil, partly paved. As a result of climate change, storms which were expected to occur

once in $10$ years are now forecast to be the equivalent of once every $25$ years. For this case,

$i=4,\frac{320}{t+27}$

The city responded by requiring houses to redirect their roof drains to gardens, and the highway runoff

to swales, thus changing the nature of the watershed to the equivalent of a poor grass surface. Would

these measures be sufficient so that the existing storm sewer system would not be overloaded every $10$

years? Justify your answer with calculations. $(10$ marks$)$

NOTE: You will need to use additional information from one or more appropriate sources. Give

details here: