High performance Turf Reinforcement Mats - Do they work? 1

[nutbutter]

Hey all,
I was just wondering about High-performance turf reinforcement mats. I've designed a rather large detention basin and our usual practice is to construct a small concrete channel along the bottom to prevent erosion from large flows. In an effort to maintain some kind of aesthetic value, I was contemplating using high-performance turf reinforcement mat instead of concrete for a channel through the basin. This would allow for a grass/vegetated channel.
Do these mats really work that well? I was considering "pyramat", a product I learned about at a Contech seminar. I think it would probably be cheaper than a concrete channel (but I'm not sure). I just want to make sure it will work well. There will be probably 200 cfs of flow through a 20-ft channel along the bottom of the basin for the 25-year storm. Does anyone have any experience using "pyramat" or other similar turf reinforcement mats in this type of situation? I just think a huge 300' concrete channel through the basin would look very bad. I'm also going to try to fill the basin with native vegetation that will facilitate bioretention activity (albeit minimal).

Any advice?

Peace,
Stoddardvilla, PE

 

[LHA]

I've spec'd Pyramat - as well as many other TRMs from them, and their competitors - often. I can not vouch for if it will hold up to the flows you are expecting, but generally these TRMs are as good as riprap, and do work if used in applications appropriate to their spec.

One thing to keep in mind though. The primary function of the concrete channels in basins is to help increase flow to drain the basin during small inflows. They do this, of course, due to a lower resistance than grass, earth, riprap or...TRMs. While Pyramat will most likely work nicely for preventing erosion, I so believe it may hinder drainage of low flows. I would check a min velocity at whatever its Mannings value is during, say, a 1" runoff storm.

Remember, amateurs built the ark...professionals built the Titanic. -Steve

 

[ccor]

I have had mixed success with TRM's here in Steamboat Springs, CO. Its semi-arid, but the rainfall we do get can be very intense. We are lucky to get grow-in in 3-years so we have experienced some of them peeling in intense storms because of inadequate grow-in.

 

[nutbutter]

Thanks for the replies. I have a couple more questions.

Iha: Do you think that the flow resistance would be an issue if the channel is about 2%? I figure that 2% is the minimum to go on pervious areas to ensure adequate drainage. Won't this be enough for a vegetated channel lined with TRM?? I would think that the TRM/vegetated channel would allow for much more infiltration than a concrete channel, therefore eliminating any issues with roughness associated with the TRM. I don't know though, this is my first design incorporating TRMs. What do you think? I think the soils are slightly clayey though, so infiltration may not take place to a great degree.

Also, how does the cost of these high-performance TRMs compare to concrete? It seems to me that it would be much cheaper to construct a 20' TRM/vegetated channel than even a much smaller concrete channel. Is this true? I know some of those high-tech TRMs can get a bit pricey though. What do you think?

Anyway, thanks for your help. Back to work.

Peace,
Stoddardvilla

 

[LHA]

I've never put a channel in a basin for high flows, only for low flows. I design the Outlet Protection for full flow in the outlet pipe, this dissipates the energy - not exactly back to sheet flow, but similar - so the water flows slowly and evenly into the basin.

A 2% basin bottom will drain fine without a low-flow channel, especially on clay.

Bioretention will be minimal or none, unless you flatten it out to 1% max., and add some sand. Bioretention will be absolutely none with a concrete channel, as the first-slush, dirtiest water will zip right through and out.

In PA, USA, Pyramat costs about $1,250 per roll @ 85 SY, delivered, plus $2/SY installation, times 1.5, if you have to pay Union rates. Formed, flat, hand-poured, hand-floated concrete costs about $5 per SF, times 1.5, if you have to pay Union rates.


Remember, amateurs built the ark...professionals built the Titanic. -Steve

 

[nutbutter]

Thanks Iha!

 

[proletariat]

I have used North American Green matting. Their literature gives you velocity and shear limits for each product in the lineup. They also have software to help w/ the design, but I have never used it.