Photo Credit: Alex Mead
Seen above is a street that has been flooded due to a storm event overwhelming the storm water sewer system. Storm water sewers are typically designed, depending on the location, for approximately a 10 year event period. This means they can handle a storm that happens on average only once every 10 years. To design for event periods much more than this would be a poor decision due to the large increase of additional resources that would be needed to accomplish these designs. As with every engineering design problem, optimal sewer design is a balance of performance and varying measures of cost.