It's a good idea to learn something new every day. I was walking by a construction site yesterday on my way to find a back corner of an adjacent lot, when I noticed these strange-looking yellow things covered with gravel.
They are StormTech MC-4500 chambers designed in accordance with AASHTO and ASTM design standards, making them a qualified choice for use in commercial and municipal projects to contain and control storm water runoff in an underground system.
Manufactured using a high-performance impact modified polypropylene, the MC-4500 is rated by ADS for a 100-year service life. Able to handle large storm water flow volumes, it measures 5 feet from the bottom to the top of the corrugation and has a base of more than 8 feet. It can be used with a minimum of 24 inches of cover and is generally installed under parking lots. Pretty cool, right? Below are some additional pictures.
Had heard of their existence, but had never seen any until now.?ÿ Thanx.
I still cannot wrap my head around how they outlet to some positive daylight drainage reach?
I understand inlet. ?ÿEasy. ?ÿFrom the top.
But, outlet? ?ÿFrom the bottom somewhere, underground?
It is pretty flat around here. ?ÿBut they do get utilized around here.
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@brad-ott No different than a normal above ground detention pond.?ÿ Just imagine a normal pond with the chambers in the bottom to create the storage volume and the elevations of the various outlets the same as a normal pond outlet structure.?ÿ Then cover it with clean properly sized aggregate to create additional storage in the voids, cover with geofabic and top it with a parking lot.?ÿ
@stephen-ward so I picture the normal pool water surface elevation of a wet detention area as the bottom of the entire chamber system?
...so essentially the top half of a CHDPE Pipe with structural porosity cover,then final grade drainage downhill somewhere?ÿ
interesting.?ÿ I'm guessing they can't dig deeper to install the pipes they'd like to install so this is an engineering alternative to get the best solution.
thanks for sharing, this is interesting to see.
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@brad-ott They're designed as detention rather than retention.?ÿ In a detention pond (at least around here), the bottom typically has a minimum slope of -2% toward the outlet structure. The outlet structure has a small orifice at the base (1-2") with a cage of aggregate wrapped in filter fabric to keep trash from fouling the small outlet pipe.?ÿ For small storm events all the water is retained and slowly released by the small outlet pipe.?ÿ Storm events larger than the pond design will cause the water to hit the overflow.
Here's a few pictures of one I laid out and did the as-built on a few years back.
This is the pond with geofabic before the chambers and gravel backfill were added.
This is the entrance header. The pipe from the storm drains is on the left. The header has a sump to catch sediment, then the water flows into the pipe the guys are working on.?ÿ The outlet on the right side is at the same elevation as the inlet, both are well above outlet into the first row of chambers. This way anything that bypasses the sump gets trapped in the first row of chambers. The first row of chambers has a double layer of woven?ÿgeofabic that can withstand being cleaned out by a vac-truck.?ÿ
The 6" vertical pipe at the far end is attached to a 6" pipe that runs the length of the pond and is the primary drain for the pond.
The unconnected stub on the outlet header is a 12" overflow for when the pond is near capacity and both headers are topped with open grates so that in a Noah's Arc situation the water will simply flow overland to get to the nearby creek in this case.
This is a snippet of the as-built of the underground detention pond.?ÿ?ÿ
@stephen-ward thank you. ?ÿVery helpful!
Do you have some local supplier that helps with volumetric sizing and even maybe with hydrologic storm flow modeling??ÿ
@brad-ott I'm just a surveyor spouting off what I've absorbed over the years.?ÿ I know that Superior Drainage Products supplied the chambers and headers for that project.?ÿ The engineering was by a local firm but Superior may have provided input or support.?ÿ I know I was able to find enough info on their website to figure the displacement of the chambers and the end caps to prove a project manager wrong on his calculations for the quantity of gravel backfill required.
When I think of detention storage I am thinking of hundreds of acre-feet, not thousands of gallons.
But, there is a use for anything in the right situation with the proper design.?ÿ The legally insane architex that were designing our school district's high school building a dozen years ago wanted all parking areas to be porous and covered with sod.?ÿ Fortunately, the school board nixed that foolishness and the related exorbitant cost to install such a system in the middle of a cow pasture.?ÿ Much of what they designed was ultra-energy- and environmentally-conscious.?ÿ Now, we get to pay triple prices to repair or replace the crap they installed due to failure to work over the long haul.?ÿ As an example, a control unit for a single air handling unit of standard design costs $X.?ÿ What we have had to buy is closer to $10X.?ÿ Nearly all lighting systems have already been replaced within ten years of initial use.
LEED is overly expensive to construct and overly expensive to maintain.?ÿ Do not be fooled by the shiny objects, rotating mirrors and smoke.
The first row of chambers has a double layer of woven?ÿgeofabic that can withstand being cleaned out by a vac-truck.?ÿ
Drainage systems should always be designed with maintenance in mind. I'm tired of seeing well-designed drainage systems that, through lack of maintenance, have become burdens on neighborhoods.
