Retention or Detention?

“Detention” at 15th & Murphy Blvd, Joplin, MO

Our firm, Allgeier, Martin and Associates, Inc., recently won a contract which involved stormwater design. The local newspaper wrote a brief article mentioning the contract and owner. The newspaper writer identified the project as “a stormwater retention project at the high school.” This prompted our Hydrology and Hydraulics Guru, Dr. Charles Patterson, to make sure I, Gabe Lett, the Marketing Guru, understood proper design terms. Therefore, I enjoy working with very bright engineers who love what they do!

Charlie writes, “These are the extremely rigorous definitions (so, I usually do not correct people on it) but, if we write it down, it should probably be a little more exacting:

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Retention pond – retains.  This would be what you would see in Arizona where the developments are typically required to keep rainfall on site so it can evaporate and is not allowed to run off from the site. An example of how a retention basin would be used in Missouri – it would be used around a tank that has a potential pollutant risk. The retention basin would have enough volume to keep all the pollutant if the tank were to bust and will prohibit a release of pollutants into the environment.

Detention pond – detains or delays/retards, a.k.a. slows down the release (to reduce the peak runoff) but basically nothing is retained. Like a juvenile detention center, they only keep them for a while and then let them loose.

1. Wet detention basin – has a normal pool of water but the floodwaters can flow through the basin albeit, at a decreased discharge rate (due to the storage).

2. Dry detention basin – often has vegetation growing in the bottom and only has water for a few hours after the rainfall event.  If it is also a water quality basin, it might hold water for 24 to 48 hours.

Engineers often incorrectly use retention for wet detention ponds, or use it interchangeably with detention at any time… so, I am SURE you have heard it incorrectly for years 😊

For the most part, detention basin and detention pond can be interchanged but some people think ‘pond’ means it always holds water.”

I appreciate when engineers take the time to inform and educate. I am a better professional services marketer for it. Therefore, I share it, so you benefit from better understanding how and why engineers are vital to the planned functioning and protection of infrastructure. Thanks, Charlie, for helping us all better understand how stormwater is mitigated to protect property, the environment, and life!