LID Stormwater Techiques 1

[martin888888]

Does anyone know what the advantage of LID Stormwater techniques (rain gardens, etc) vs conventional methods (ponds, Swales, etc)? The only real advantage I see is the reduction of land area used for the installation of a pond.

 

[beej67]

Define "advantage." It's helpful to know which stakeholder you're representing in the complex web of stormwater interests.

The main environmental advantage is in promoting groundwater infiltration, which reduces runoff volumes instead of simply peak flows. The volume problem is the primary problem that drives stream erosion, which leads to both degradation of habitat and to increases in TSS loads which can impair a stream under the Clean Water Act.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[martin888888]

All stakeholders. From an environmental standpoint, from a costs standpoint, from a construction standpoint, etc. The causes and problems of storm water runoff from developed land are known and documentented.

My question I guess is why is a rain garden or pervious pavement(which is a horrible option for many reasons)any more environmental freindly then a well designed retention pond? A retention pond takes away valuable land mass but if that is not an issue I dont see a reason why not to use one.

I always here people throw around the terms that you want to use LID measures to construct an environementally freindly site and get "credits" for it. Conventional methods like a rentention pond would do the same exact thing. I have yet to see a jurisdiction that gives you "credits" for using LIDS.

 

[Twinkie]

LID (depending on what technique employed) will promote volume reduction and water quality. Your typical detention pond may get you some volume control, but typically release begins immediatley.

Raingardens, wetlands, veggie swales, etc all promote evapotranspiration and biodiversity as well.

Green roofs can reduce runoff volumes for lower level storms, and provide aesthetics on an otherwise bland rooftop.

Pervious paving has been a well documented success over the past decade, and I have employed this option in countless projects in my area of practice, all with great success.

 

[martin888888]

A well designed rentention pond will do the same as LID measures. It promotes infiltration, volume reduction, and water quality. It will not have immediate release.

There are a lot of downfalls with pervious pavement here in the northwest with all the rain. The main being that it clogs really quickly unless constantly maintained. We have also seen many issues with maintence on these.

 

[Twinkie]

I think you are referring to what we call in the NE a "wet pond." Permanent pool, sediment forebays, wetland plantings, reverse drain that pulls from the bottom?

We typically do these in areas with high groundwater and impermeable soils. You really need a decent sized drainage area to maintain the base flow. I classify this approach as LID.

 

[martin888888]

No, A retention pond will infiltrate water and normally has a draw down time. There is not a permanent pool. It is a conventional stormwater method.

 

[civilman72]

One of the goals to LID for stormwater is to attempt to mimic historic conditions, particularly from a groundwater recharge perspective. Creating a large impervious area and draining all of the surface runoff to one regional retention pond (infiltration point) does not come close to emulating pre-development conditions.

 

[beej67]

My question I guess is why is a rain garden or pervious pavement(which is a horrible option for many reasons)any more environmental freindly then a well designed retention pond? A retention pond takes away valuable land mass but if that is not an issue I dont see a reason why not to use one.

I always here people throw around the terms that you want to use LID measures to construct an environementally freindly site and get "credits" for it. Conventional methods like a rentention pond would do the same exact thing. I have yet to see a jurisdiction that gives you "credits" for using LIDS.

First off, a note about terms. You're saying "retention pond," and later you mention that it will infiltrate water. Please realize that many engineers across the country don't have soils that can support that sort of BMP, so when they hear the words "retention pond" they're thinking "detention pond" instead. That's the source of some confusion above. Do note that true "retention" is not at all a common method in most of the country, because very few places have the soils to support it.

Now on to your questions.

In many areas of the country, mine included, classic "retention" ponds are already considered a LID technique! The LEED system gives credit for them, for example. If you can make them work, retention ponds are some of the best BMPs available, so you're setting a high bar for comparison.

Infiltrating through a porous pavement or infiltrating through a retention pond are both about equal, in my opinion. I've seen some studies stating that frequent inundation of the base course of a porous pavement section will actually create an aerobic bioreactor in the base stone, which will help to process and eliminate hydrocarbon pollution. So that would be a bonus over retention ponds, but how much bonus hasn't been studied heavily. There are other studies that say the same thing about rain gardens - that they tend to trap bad stuff in the engineered soil mix and then it gets processed by the bioretention plantings in the swale. Again, it's a nice intuitive conclusion but I'm not sure it's exhaustively supported by research. Research on stormwater BMPs tends to be pretty sketchy, because you don't have a wide enough field of data to draw firm statistical conclusions.

Depending on the site, you may be able to get a lot of cost benefit out of LID techniques, because they focus on reduction in impervious area of the site. Basically you save money on your retention pond. If you make every landscape island a bioretention swale, and add them all up, you need less land for the pond, which increases the development yield on the site. Another LID technique I've commonly seen is rainwater cisterns for landscape irrigation. In drought prone areas this could save you huge amounts of money. Depending on where you are in the country though (riparian vs prior use allocation) cisterns could be flat illegal. East of the Mississippi you're probably fine, West you should check. If you're in the northwest, I doubt this is a concern for you. You might be able to flush your toilets with the cistern water though, and save yourself money over the life of the project that way. (and also pick up some LEED points if you're in to that sort of thing)


Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[Dbxazd]

The advantage of LID (Low Impact Development) or ESD (Environmental Site Design), naming conventions depending on where you are, is increased water quality. These type of BMPs are better at mimicking predevelopment conditions because they typically allow runoff to quickly infiltrate closer to the source than a conventional pond facility which typically is located at the low point on a site. The idea is to get the runoff back into the ground as quickly as possible - thus groundwater recharge. Also, with respect to water quality, many of the LID/ESD best management practices allow for better nutrient reductions (ie: nitrogen, phosphorus, etc.). This is critical for sites which drain to impaired waterbodies. A good example is in the mid-Atlantic region where there is the Chesapeake Bay TMDL (Total Maximum Daily Load) which is a "pollution diet" for that waterbody. Through LID/ESD applications, one can quantify the reductions of pollutants from a site by utilizing BMP pollutant removal efficiency rates. LID/ESD practices are shown to be much more effective in pollutant/nutrient removal than the conventional wet pond. Several state are implementing LID/ESD practices as requirements. The State of Maryland has good information on their website (MDE-Maryland Department of the Environment) regarding this. Also, another good reference is the Center for Watershed Protection. Hope this helps.