[Philip (PJ) Benenati]

This is a legitimate concern and one that our office studied when designing curbside bioretention cells in DC as part of The Yards project. We started with the city of Portland’s standard detail for poured-in-place concrete walls and then reviewed several alternatives, hoping to find some cost saving. We studied a wood-lagging system, a 1:1 slope within the cell, a proprietary slope stabilizing product, and even metal sheet piling. Most of these seemed unrealistic as far as cost, durability, and maximizing water storage volumes. Our best option, and the one that we pursued, was a precast concrete vault, with no bottom face and root opening on the back and sides of the vault. This did cost out under CIP conc walls because of the quality we were installing.

If you’re interested, I can attach a pdf of the vault design and photos of the installation.

[Philip (PJ) Benenati]

I just wanted to share a few projects from Seattle:

1. Taylor 28 Apartment Building (Mithun) – Urban plaza/streetscape with several bioretention planters and porous concrete along the curb
2. 2201 Westlake Plaza (Berger Partnership) – Urban Plaza incorporating art-planters and bioretention
3. Piper Village (Berger Partnership) – Streetscape with curbside bioretention cells. Permeable Pavers and constructed wetland are also present on the site.

[Philip (PJ) Benenati]

Claudia. I’m not familiar your soil conditions in SC but I’ve heard that as part of the regular maintenance for these systems, periodic cleaning of the pore openings is required. I’ve heard that this can be done with a street cleaner or pressure washer and that this should be done to remove the buildup of fines 1-2 times a year. The Florida Aquarium in Tampa has done research on permeable pavement options in the SE. this link, http://www.lid-stormwater.net/permpavers_benefits.htm, has some helpful resources including the final report from the Aquarium study.

Wes. Thanks for the pic of that town in WA. i wasn’t able to find any other clear images on the web. Can you post the best of what you have? Thanks for the example.

[Philip (PJ) Benenati]

Librety Hills in Charleston, SC used permeable pavers in the alleys of the development. Oak Terrace Preserve in Charleston also uses permeable pavers in the alleys and also used curb-side bioretention swales that flow to pocket parks that treat stormwater. The Johnson Medical Center in Clayton, NC uses a large bioretention cell in its parking lot (not really green “streets” but a nice example).

[Philip (PJ) Benenati]

Philip, for your streetscape projects were you using bioswales or bioretention planters?

[Philip (PJ) Benenati]

Thanks I will make sure to look through your photos.

Since our installation our raingarden has apparently received several large storm events with the berm holding up and the system draining well. I will certainly be watching it over time to see its performance. The raingarden is currently under 4 ft of snow, so the spring may be a good time to judge how durable it is.

Has anyone had experience working these systems into urban conditions?

[Philip (PJ) Benenati]

That does sound like a great project. Do you have any photographs or drawings you are able to share?

This past summer I was volunteering with an environmental non-profit organization, DC Greenworks, and had the opportunity to help design and retrofit an existing swale that eventually sheet-flowed off site, to a bioswale and raingarden. We did the installation with the help of 20 local high school students as part of the Mayor’s Green Summer Job Corps. It was a great project but physically straining from using primarily shovels and pickaxes to do all the grading.

The existing berm and swale were sloped downhill, north of the arched walkway in the plan. At the end of the swale, the berm stopped and water sheet flowed down the remaining slope, causing erosion issues on the hill. At this location we cut back into the slope and leveled off then base of which would be the raingarden capturing and infiltrating this runoff. The cut material from the slope was relocated to the other side of the raingarden to form the new berm, which connected to the existing berm and enclosed the garden.

The extents of the existing swale were defined using a post and chain fence and then let to naturally grow from lawn to meadow. The meadow condition will help slow the water and pretreat it before entering the raingarden.

[Philip (PJ) Benenati]

Tanya, did you have a wetland ecologist involved with your stormwater wetland project? I am in Seattle and pursuing 2 certificate programs here, one in LID and the other in Wetland Science and Management. One thing that has been emphasized is that when designing wetland mitigation or even stormwater wetland systems, it is important to design within the larger landscape context to relate wetland functions from your wetland to adjacent or nearby systems. Sometimes that means designing a wetland with similar functions, sometimes it means adding other functions or habitat conditions that are no nearby. Has anyone had experience with this?

[Philip (PJ) Benenati]

I’m usually not a big fan of tree grates, however I actually think that the grate does provide a very important function is a system like this. In any curbside Bioretention system you will have to manage the gross pollutants that will inevitably build up in the system, i.e. cups, wrappers, other litter…. In an exposed system you will see all of this debris on the surface throughout your plant material. The grate on the filterra hides this debris and litter until you open the grate and remove it twice a year. This also reduces your maintenance needs to twice a year as opposed to the continuous maintenance you will need with an exposed system.

So I would actually say that this application would be appropriate for any urban environment where you are likely to collect litter, especially situations such as back of house or large commercial parking lots.

[Philip (PJ) Benenati]

Clay don’t hate too much on Filterra. I used to feel very similar. My strongest concerns were mainly with the aesthetics of the unit, specifically the concrete exposed on the surface and the fact that the plant material had to be either a shrub or flowering ornamental tree. I was also, originally, under the impression that every 5 years or so these units required major maintenance, including the replacement of the filter soil media and plant material.

All of these concerns were recently laid to rest for me though. Back in June I attended a BMP Maintenance Seminar and met with representatives from Filterra. I witnessed first-hand a full maintenance routine for the system. Filterra requires very minimal and infrequent maintenance. All that is required is to twice a year open the top grate, which has been hiding all of the litter and debris collected, remove and dispose of all litter, debris and top 2 inches of mulch, and then replace the top 2 inches of mulch. My original impression of having to replace the filter media and plant material every 5 years was apparently inaccurate. Filterra assured us that the only maintenance required is the process which I just described. I think that is a bit ambitious and believe that these systems probably have a similar life span to that of typical Bioretention, which should last approximately 20-30 years.

My aesthetic concern regarding the concrete being exposed on the surface is no longer an issue since Filterra has just recently released a new recessed unit. It is very similar to how a paver tray might be use over a manhole or utility vault, where now you can surround your tree grate with pavers, mulch, or even lawn. I have attached the Recessed Unit cut-sheet.

Filterra has also just recently released a larger unit to finally accommodate a street tree application. The unit also has concrete knock-out locations on 3 walls of the units, which will allow for root connects from the unit to adjacent soil or structural soil. I have also attached this cut sheet and their recommended street tree list.

Overall I’ve changed my point of view on the Filterra system and feel that in the right application this can be a very successful tool.

[Philip (PJ) Benenati]

what i love most is simply looking at the work differently. Everywhere you go you think about “how and why was this built” and you start to notice funny things like spatial relationships and circulation. I know its kinda nerdy but that’s part of the fun…

[Philip (PJ) Benenati]

Our office has been toying with the idea of purchasing it but has not yet committed. i know several of our offices out west are using it and apparently having a lot of success. The main challange I see, and its probably a good thing, is that it requires you to re-orgainize your details library and CAD standards. Not quite sure how to impliment it into our office yet but the demo they gave us was amazing! any suggestions on how to easily work it into existing CAD standards?

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