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Studying Rainfall near Warren, Michigan

August 20, 2013

How much it rains in a day affects infrastructure and people.
Is your flood insurance agent up-to-date on it all ?
The perceived occurrence of high-intensity storms
occurring more frequently than expected has
prompted an update of rainfall charts (statistical estimates).
Previous rainfall events for Michigan over a
24-hour, 100-year value, were exceeded 71 times.
(only 21 occurrences were actually expected using old charts)

A 100-year rainfall has a probability of 0.01, or 1%,
of being equaled or exceeded in any one year.
It is not to be assumed that only one 100-year event
will be observed every 100 years.

A newer study utilizes data from 76 hourly and
152 daily rainfall-recording stations
throughout Michigan, along with
81 Southeast Michigan Council of Governments
short duration rainfall-recording stations located
in 5 counties in and around Metro Detroit.
MDOT_MS4_Final Report _Rainfall Intensity.pdf ( 2002 )

An Intensity-Duration-Frequency chart is merely
a graphical representation of the probability
that a given average rainfall intensity will occur.

Is it possible to get 7 inches of rain in 24 hours,
sure it is, but no one would expect numerous occurrences
within a year, or plan to build infrastructure to handle it.

~~~~~~~click on any picture to enlarge it~~~~~~~

Recurrence and probability

Recurrence and probability

Michigan Rainfall IDF Estimates

Michigan Rainfall IDF Estimates

Isopluvial Rainfall 2 year 24  hours

Isopluvial Rainfall 2 year 24 hours

Isopluvial Rainfall 10 Year 24 hour

Isopluvial Rainfall 10 Year 24 hour

Isopluvial Rainfall 100 year 24 hour

Isopluvial Rainfall 100 year 24 hour

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  1. Gravity and sanitary drainage | Red Run

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