stormwater storage 2

[Jmg]

I am researching different types of underground stormwater storage, and am wondering which is perferred pipe or chambers? Any comments and/or insights as to why one is better then another would be greatly appreciated.

 

[n3rei]

Underground SWM storage is probably best summed up as the best aproach is the cheapest approach. I have heard nightmare stories of collapses with chambers, but on the same token good results have been achieved. The recent onsloght of not using CMP in dams probably should be considered applicable for Under Ground Storage, since collapse of rusting metal and joint failure would also cause collapse of the roadway. The safest method is stone, but costly also, and sediment could clog the voids. Underlying soils would be the key to deciding which system suits the project in conjunction with the size required. Again cost is the issue for larger storage requirements. So while investigating this area keep in mind cost, cost, cost, and if at all possible avoid underground storage and go with a more conventional, and easy to maintain and inspect, basin system.

 

[VR1963]

Based on my limited experience, I would not use chambers. The one project I used them required complete excavation to restore capacity, the bottom was completely fouled. Use a pipe system that permits some level of cleaning.

 

[cvg]

underground storage is a perfectly acceptable method, however, do not rely on infiltration into the ground. A pump must be utilized to drain the basin. Most agencies I work with also have very strict requirements for material types, pump systems etc. Check with your city development review dept. first.

Chuck
cgopperton@stantec.com

http://www.stantec.com/

 

[GPM]

As one who is in charge of the storm water systems for a municipality I cringe at the thought of using pipes or chambers for SWM facilities to be owned and operated by a municipality. Typically these types of structures are more in the interest of saving money for the developer and not much thought put into the long term costs associated with operations and maintenance. Typically one should complete a life cycle analysis to determine best material based on soil profiles, pipes vs chambers vs ponds...etc. and future replacement costs. I'm not aware of any studies that may have been done with respect to long term maintenance of tanks but also have concerns over freezing, cleaning, gas buildup....etc. Perhaps if anyone is aware of such studies please forward any information you may have.

 

I have found one product esspecially usefull for underground detention. StormTrap is a concrete "Box Culvert" type system that is priced competitvely with plastic pipe and cmp.
I have found that most city officials will appove a concrete system with little hesitations and that my clients like the idea of concrete and not plastic or steel.

Justin

 

[Bayou]

Underground storage is find, but not too practical depending on your storage amount. For 1 ac-ft of storage,
you will need 1-10'x10' box 433 feet long. That is alot
of cost. While excavation of 1 ac-ft averages about $5000.

 

[RDWCE]

QUITE FREQUENTLY WE CALL OUT FOR INFILTRATION CHAMBERS AS A MEANS OF DETAINING SMALL VOLUMES OF RUNOFF. HOWEVER THEY ARE A SOLUTIONT TO GETTING THE PROJECT PASSED, I FEEL THERE USE IS POINTLESS IN SMALL APPLICATIONS, AND CAN BETTER BE SERVED WITH PIPE DRAIN SYSTEMS, AS THE COST OF INSTALLATION, FAR OUTWEIGHS THERE USEFULLNESS

 

[gibfrog]

1) The underground rock-bed. This system uses a rock bed (void area 0.3 -0.4, no limerock of any form, quartz type rock/gravel is prefered in SW FL) to store the water under concrete pavement. The water is distributed in a corrugated perforated high density polyethylene pipe (HDPE) pipe (such as ADS Drainguard w/o sock) system and the whole bed (bottom & sides) has a permeable geo-textile (mirafi 140-n or approved equal) while the top has a impermeable liner (20 mil pvc). The inlets are usually catch basins with a 2' minimum sumped area to help catch silt and a 12" dia bottom opening w/fabric & gravel to provide drainage. Silt will eventually kill the system, even with terminal cleanouts because the owner will not properly maintain the system.

2) The conventional vault system uses concrete block walls and a precast concrete deck. This is simply an underground vault with a minimum of 4' vertical clearance for maintenance and a minimum of (1) 30"x30" accessway, usually placed under the pavement. AVOID UNDER BUILDING STORAGE AND PERCOLATION, unless a special analysis is performed. Make sure that there is adequate access for maintenance to all areas of the vault. This system is usually the most expensive, but the smallest area. A variant is to vault a buffer area and use a wood deck (pedestrian loading only) to cover the vault. This system also requires maintenance.

3) Infiltrator (semi-elliptical HDPE pipe) systems. These systems are very difficult to maintain, but not very expensive. Picture a ~15" high span, maybe 30" wide connected by a 4" diameter pipe nipple. These can be stacked into numerous perpendicular rows, but pay attention to the distribution system. The bottom is a non-woven fabric (mirafi 140n or approved equal). The inlets should be via the catch basins with a 2' minimum sump and bottom opening.
4) Alternate such as large diameter plastic pipe (usually HDPE). See the rock bed system w/o the rock.
We design these systems with a 50% percolation safety factor based upon a double ring infiltrometer percolation test and ground water mounding analysis unless the seasonal water table is 10' under to bottom of the underground system (5' for CA<2.0 acres)

 

[RobertAllan]

In my experience chamber systems offer much more than pipe systems. Designing is easier and more flexible. They're like a modular structure that can be designed at lesser costs since they don't require costly elbow's and T-sections.

Infiltration could be factored into the design of a subsurface storage system if the site's soils have adequate percolation rates. It is both conservative and conscientious to design a subsurface system without taking into account the loss of volume through infiltration but none-the-less infiltration should be a design initiative when appropriate.

Replicating the pre-developement infiltration, with an appropriate design, maintains the subsurface hydrology. Many times the focus of stormwater management plans only target the issues imposed from changing surface hydrology while they neglect the chnages in subsurface hydrology.

 

[chadmcm]

We've utilized both pipe storage and chambers for detention and retention of runoff. The cost tradeoff for us is usually related to particular site constraints - depth to groundwater, the amount of fall that's available through the system, the area that can be utilized, etc. We find that larger diameter (48&quot pipe tends to be cheaper than chambers where it can be used, but we've had very good results with the Rainstore product recently.

 

[Gosox]

I have had problems with the rain store products filling up with fines overtime due to the fact there is no way to access the system after the fact . Just a Y.F.I.

 

[halleys5]

Check out the Rainstore system at

http://www.invisiblestructures.com

I used this product to detain over 30,000 cf. It is <$10 per 3.5 cf storage (module only), the modules are 94% void making the detention area nice and compact. I preceded it with a stormceptor to reduce settlement. Don't forget to oversize for the volume lost to sediment as the units are non-accessible after construction.