Here is an example showing the Runoff, Rainfall and Infiltration losses when you use the wrong interval based on the hyetograph time series.

__1.__

__Figure 1 shows the Rainfall, Runoff and Infiltration for a time interval of 5 minutes which matches the hyetograph interval, the raingage has units of mm and is the total volume over the interval__

__a.__

__The volume of rainfall is 20.03 mm as it the total rainfall over the interval__

__b.__

__The rainfall, runoff and infiltration graphs are smooth__

__2. ____Figure 2 shows the Rainfall, Runoff and Infiltration for a time interval of 1 minutes which does NOT match the hyetograph interval, the raingage has units of mm and is the total volume over the interval__

__a.__

__The volume of rainfall is 20.03 mm as it the total rainfall over the interval__

__b.__

__The rainfall, runoff and infiltration graphs are not smooth as there is a gap of no rainfall between minute 1 and 5 for all of the hyetograph time intervals__

__c.__

__The peak rainfall is higher as the rainfall is over 1 minute instead of 5 minutes__

__d.__

__The peak runoff and infiltration rates are also higher but this difference depends on the roughness, depression storage and infiltration parameters of the catchment__

__e.__

__The slower the runoff the more Figure 1 and Figure 2 runoff will look alike even though the rainfall is the spiky versus smooth (Figure 3).__

Figure 1. The Rainfall, Runoff and Infiltration loss for a gage interval of 5 minutes which matches the Time Series Interval |

Figure 2. The Rainfall, Runoff and Infiltration loss for a gage interval of 1 minutes which does not match the Time Series Interval |

via Blogger http://www.swmm5.net/2013/10/the-effect-of-wrong-raingage-interval.html