Voodoo Hydrology: “In the absence of flow data, we make the Big Assumption,” says Andy Reese


Note to Reader:

Andy Reese is a leading American water resources engineer; and is a popular writer and speaker. He and Dr. Thomas Debo are co-authors of the best-selling textbook Municipal Stormwater Management. In February 2013, his webinar on Voodoo Hydrology triggered an overwhelming response in the United States as well as in Canada. Back by popular demand, Andy Reese will be delivering a follow-up webinar on Voodoo Hydrology on January 30.


Webinar Back by Popular Demand: “Andy Reese on the Pitfalls of Voodoo Hydrology”

“Urban hydrology, as commonly practiced, is an inexact science at best. If we were omniscient, we could do an exact job of urban hydrology. Instead, we rely on engineering judgment and guesswork, ultimately striking a compromise between accuracy and data availability, and resulting in an answer that is close to correct,” explains Andy Reese.

Andy-Reese_120p“All uses of rainfall instead of flow data make the ‘Big Assumption’. We know that there is only one 10-year peak flow for our site. If we were able to ask some Omniscient Being, she would be able to tell us the current one-in-10-year peak flow to 10 significant digits. There is only one. Our problem is trying to estimate it.”

“Perhaps, if we make enough estimates of enough factors, the errors in estimation, high and low, will average out to the right answer. This is where voodoo really comes in handy.”

“The good news is that, as my old friend Dr. Tom Debo says, ‘Who can prove you are wrong?’ Well, the Omniscient Being can, but is probably busy elsewhere,” concludes Andy Reese.


Forester University is hosting a Live Webinar featuring Andy Reese on January 30. For information about learning outcomes and how to register, click on Voodoo Hydrology— Pitfalls of Urban Hydrology Methods & What You Need to Know

Also, click on Voodoo: Magical practice considered to be a form of black magic, but also considered a religion to some to read the 2006 article by Andy Reese when he coined the term Voodoo Hydrology.

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