ADS FAQs - Inflow and Infiltration

The specified minimum inter-event time may impact the results of an I/I analysis. How big of an impact is there when you vary this parameter?

by Jim Hunt|Published December 31, 2025

The specified minimum inter-event time may impact the results of an I/I analysis. How big of an impact is there when you vary this parameter?

The number of discrete rainfall events that you extract from a continuous time series of rainfall data is inversely proportional to the specified minimum inter-event time. If you use a smaller value for the minimum inter-event time, you will have a larger number of smaller rainfall events. If you use a larger value, you will have a smaller number of larger rainfall events. In terms of an I/I study, you seek to match rainfall with a flow response in the sewer. Therefore, think of the minimum inter-event time as a default value, not as an ideal value. As you review the I/I responses, you will find cases where the default values work out just fine, and you will find other cases where individual adjustments need to be made. Combining two adjacent rainfall events into one larger event is a common example. Use a reasonable default setting to do most of the work for you, then apply your engineering judgement to adjust other Rainfall Events as needed.