Differences between Retention ponds, detention (wet and dry) ponds, infiltration ponds (Sec 4)

[Benjamin Haim]

Hey guys!  I need some help here.  I can't seem to get clarification of these differences, and if the terms are actually somewhat interchangeable.  

Site engineering seems to define ret. ponds, det. ponds and infiltration ponds (but doesn't give much info on what an infiltration pond is).  Time saver standards defines two different kinds of detention ponds- wet and dry, but it seems like a 'wet' detention pond is just an interchangeable term for a retention pond.  I'm pretty confused.

What source should I rely on here?  Does anyone know of a source that would provide more straightforward definitions?

Thank You!

[Kirsten Radomski]

I would say to look carefully at the diagrams in Site Engineering and know the components of each type of basin.  I thought I remembered that the sustainable sites handbook had a good section on water, more on infiltration especially.  

[Emily Garavuso]

You might try using the definition from any one of the states DEC Stormwater Manuals.  I use NY's manual regularly  http://www.dec.ny.gov/docs/water_pdf/swdm2015entire.pdf 

Retention Ponds - aka wet ponds, retain water - meaning there is ALWAYs some amount of water in them.  This means you either have soils with no infiltration, a liner, or in the case of a pocket wetland your pond is in the water-table.  

Detention Ponds detain meaning they hold water temporarily.  You can have detention with or without infiltration.  Without infiltration means your detention pond will need to have a drain (either under drains or an outlet pipe).  

Infiltration Basins is a type of detention pond have to have soils with a minimum infiltration rate (for most it is  0.5"/hr) and will help recharge the water-table.  It will typically also have some sort of staged storage device to let water out at pre-developed flow rates or at the very least an emergency spillway. 

I hope that is helpful.  If you have more questions feel free to ask.  Stormwater management can easily snowball in its complexity so don't be discouraged if it takes a minute to follow all the different branches. 

-Emiy

[Maren Walker]

I found the Michigan DEQ BMP Manual to be pretty helpful and straightforward - it outlines all the different BMPS very clearly including pollutants controlled, impacts, application, relationship with other BMPs, etc.

http://www.michigan.gov/deq/0,4561,7-135-3313_71618_3682_3714-118554--,00.html

Different than the NY manual that Emily referenced though, it identifies an Infiltration Basin as synonymous with a Retention Basin, not Detention. Anyone have any further clarification? Hope that helps. Good luck all! 

[Emily G]

There's always https://en.wikipedia.org/wiki/Retention_basin 

The problem is there are numerous terms that mean the same thing.  A retention pond is a wet detention pond - both imply water is being held onto for an extended period of time. A dry retention pond, detention basin (even an extended detention basin), or infiltration basin are all temporarily holding water.  That Michigan resource says a infiltration basin can also be known as a retention basin but I would argue that is wrong because if you have sufficient infiltration the pond will only be temporary - I'm guessing there definition is thinking of infiltration of less than 1/2"/hour - but I wouldn't call that an infiltration basin (this particular page is also dated 1992 so terms could have changed a wee bit). 

Ben, Is this helping or just adding to your confusion? 

One thing I can say about CLARB is they look at your comments - ALL OF YOU COMMENTS.  So as long as you understand the key differences (one is temporarily wet, the other much more permanent) you should be set.  If you get a question that isn't clear write up why it isn't clear in the comments and defend your answer.  If you can remember one, site a source.  I wrote in comments on about 30% of my questions and passed on my first try.  I hope that it helps CLARB make questions clearer for future test takers.  

[Ray Freeman]

Im sorry.... but Emily G is flat wrong about retention ponds.

They are NOT always wet.

A retention basin is designed to retain storm water runoff. It provides temporary storage to allow runoff to infiltrate into the ground. The purpose is to attenuate both rate of release (discharge) and volume of release. Generally speaking, you don't want water standing in these in between rainstorms. Fairly permeable soil is necessary.

A detention basin is designed to detain storm water runoff. It provides temporary storage to slow the release of runoff from a site. Any ground water recharge accomplished doing this is incidental. These can be designed to have permanent pools or not. The permeability of the soil is not an issue.

A water supply reservoir stores water for use. Generally you want this to always have water in it. The less permeable the soils, the better.

A wet pond has standing water to some depth all of the time.
A dry pond dewaters itself between rainstorms.

All ponds need overflow control devices.