Question

Water us draining to a storm sewer from a watershed in east El Paso. The time of concentration for sheet flow is 20 minutes and shallow flow is another 20 minutes. What is the intensity in cm/hour that you should use for design purposes if you need to design for a 25yr, 24 hour duration storm? (Hint: Use the EP DDM)

A) 2.18

B) 5.3

C) 1.6

D) 2

Answer 1

The rainfall intensity I is determined from Intensity Duration frequency curve, which plots Intensity versus duration over various return period years.(Refer attachment for curve).

Remeber curve gives value in inches per hour and question ask in cm/hr.

With projecting answer can be closely related to option (a) i.e. 2.18

Filters or analysis to be applied for:

1.40 mins for Duration

2.25 years- Return period

3.