Pervious Concrete Dynamic System Modeling

Dynamic System Modeling -web-rev2-June2014

We have been working with architects, engineers, homeowners and municipalities to really explain how pervious concrete is a comprehensive storm water mitigation device. It has proven difficult to help people to wrap their heads around how allowing water to soak in to where it falls, using pervious concrete, is a viable storm water management strategy - so we have started to use Dynamic System Modeling as a tool to help explain what is happening in a pervious concrete slab, and how much water it can infiltrate over time.

When we use the concept of infiltration over time, pervious concrete systems provide huge capacity, far exceeding most climate’s most intense storm events. That is most easily demonstrated using a software modeling system. This allows insight as to a system’s capacity, and informs design, to ensure that the pavement and drain rock base will meet or exceed the required storm water infiltration amounts.

We have more information about this on our Pervious Concrete Dynamic Systems Modeling page, or you can contact us for more information!

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Pervious Concrete and Maintenance - Your Questions Answered!

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Recently, maintaining pervious concrete has come up several times in a week, prompting this blog post. The good news is that this conversation is happening. The bad news is that some people who are not on board with pervious are using an ill-informed maintenance opinion to shape their judgement. We here at Bay Area Pervious Concrete would like to clear up a few of the misconceptions around maintenance.

Firstly, we have found the relevance of maintenance is tied directly to the porosity of the slab itself. A healthy infiltration rate for a slab of pervious concrete is 250-1000 inches per square foot per hour. That ensures that even if the slab was 99% clogged, and the 5 year storm event was 3 inches in 24 hours (as we have here in the Bay Area), that slab would easily be able to absorb that entire storm. So at 99% clogged, the slab would take in 2.5 inches - 10 inches of stormwater per hour per square foot!

Secondly, here are three helpful resources to help with installing a good slab, maintaining it and the fixing a worst case scenario:
1) In order to make sure you get your healthy infiltration rates, an experienced and qualified contractor is required. We have performance based specs that you may review, so that you can be sure to get a good contractor and get a great pervious concrete installation! We also have a BAPC PolishedTM Pervious Spec that we will send at your request.

2) Regular maintenance that can be done, if there is a budget and a desire for a plan. We have put together a maintenance manual that we give to clients at their request when we finish work for them. This gives an idea what you can anticipate, allows one to set up a maintenance schedule, and has resources to call if clogging does occur.

3) Pervious concrete can recover porosity after clogging over years as shown from a research paper from Florida that came out a few years ago. The paper shows several slabs of unmaintained pervious ranging in age from 6 to 20 years old that were able to recover significant infiltration after a pressure washing, vacuuming or a combination of both - after YEARS of neglect. So, no maintenance, no problem!


Do you have any unanswered questions about maintenance and pervious concrete? Submit them here, and we may add them to this post!

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Stormwater Sleuthing - Episode 2 - Palo Alto

David Liguori is back in the field, this time comparing a long sloped asphalt driveway with a neighboring long and sloped pervious concrete driveway during a rainstorm last year.



What did you think? Do you have a Stormwater Sleuthing location (in the Bay Area) that you would like David to investigate the next time it rains? Let us know in the comments below or contact us here. Thanks!
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USGBC Greener Builder - a fantastic conference!

Lauren Wray, our Director of Marketing, attended the USGBC’s Greener Builder Conference last week. Apparently the Greener Builder COnference is even GREENER then the Green Builder Conference that occurred in November! This conference did not disappoint. From the opening panel, pictured below, featuring Jeffrey A. Birdwell, Michael Deane, Kevin Hydes, Kirsten Ritchie and moderated by Cliff Brewis, the focus was on leading edge sustainability, and strategies to get regenerative planning and innovation into the building industry.

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There were good options for every panel, but as pervious concrete sub-contractors, we went to the subcontractor panel, hosted by John Home and Jeff Swinyer of Rudolph and Sletten, pictured below.

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Lauren, pictured below, was interested in the drive toward clear performance specs to allow for differentiation at the sub-contractor level. As a pervious concrete subcontractor, we differentiate ourselves with our embrace of leading edge technologies for mix design and installation. Unfortunately, many current specs don’t reflect the progress in the installation, mix designs, equipment and curing materials that has developed in the last few years.

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The next panel we attended discussed Environmental Product Disclosures (EPDs), a labeling system that discloses the resource footprint of the many materials that go into the built environment. The panel also included the next iteration, the Health Product Disclosures, which discloses the materials and chemicals that have been proven or correlated in causing health problems for humans.
Central Concrete, a sponsor of the event, has been heavily involved in the EPD project for disclosing the materials for the concrete industry. Below is a photo of the panelists from this panel.

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The last panel of the day went over Net Zero Energy buildings with John Andary and Scott Shell, pictured below. It was a fascinating look at what is currently possible with technologies now: buildings that use as much energy as they make. The building case studies discussed also illustrated how livable and workable these spaces were, with thought for passive heating and cooling. Many of the designs features windows that bounced daylight far into the building envelope, as well as fresh air ventilation. It was a wonderful talk, even though their topics stayed primarily inside the building envelope.

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The final speaker, Jason McLennan, pictured below, gave a wonderful talk on self limits. His talk really stood out for his candor and optimism. For a young guy, has accomplished quite a bit in the green building spaces. Currently he is pioneering the Living Building movement.

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After his talk, Jason McLennan was joined by George Salah, of Google, and David Gottfried of the USGBC. They discussed everything from George’s living-building home construction project to Jason’s motivation to do the work that he does: “I give a shit.” That was wonderful.

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FInally, after it was all over, we found that there was a fantastic array of beers, wine and snacks to round out the day’s networking. It was a great event, and one we will look forward to attending next year!

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A BIG thank you to Charlie Nucci, who took these photos at the event. You can find more about Charlie and his work at his website here.

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Water Conservation Showcase a success!

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Our own Lauren Wray attended the USGBC and P&E’s Water Conservation Showcase this year. The Bay Area Pervious Concrete Booth was in this video, above, and photos of Wray and pervious concrete made it into PG&E’s “Currents”, a P&E news site. Check out the video and let us know your thoughts! Did you attend the Water Conservation Showcase this year?

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The Rational Method and Pervious Concrete

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The Rational Method is used by many storm water civil engineers to understand storm water runoff. Frequently it is being invoked to understand the impacts of pervious concrete. Frankly, the Rational Method has no place designing with pervious, and this is what we are going to discuss.

The simplest reason being, the Rational Method is there the allow engineers to size the necessary sewer line appropriate to the runoff on the site. However, when pervious concrete is well designed and installed for most or all of the parking or access areas, there will be no runoff from that area. It is even possible, pending some limitations**, to capture most if not all of the adjacent runoff from impervious roofs or other impervious. That would make the runoff coefficient 0 or even negative. Given that, Q becomes zero, or less then zero. At that point, no drain pipe is needed to carry away the storm water, and the Rational Method is not the appropriate method for quantifying storm water.

This hints at the total shift that is before us - the way we previously understood hardscape and the associated negative externalities (runoff, storm water pollution, heat island effect, aquifer depletion) is turned on its head. Now these previous negative externalities are accounted for and reversed, and we are able to maintain the preferred hard & durable surface with pervious concrete. Pervious concrete allows storm water and pollution to filter in and infiltrate, allowing microbes and soil to be the filter that they are for the rest of nature. Pervious concrete mitigates the heat island effect in 2 ways, having a high solar reflectivity index as well as allowing a water and air exchange between the soil below and air above the pavement.

But given that codes are still being written, and some building and design professionals do not know about pervious concrete and its benefits we must still use the Rational Method. So I propose a stand-in coefficient.

To review the Rational Method for those of you who don't use this equation frequently,

RationalEquation1

Q = the necessary size of the pipe to capture the runoff being generated by C, I and A.

A = The area whose runoff is being measured.
I = The rate of rainfall in a given time horizon.
C = The coefficient that is determined by the type of ground covering being measured, below you can see one version of the chart referenced.

cValues-RationalEquation


As you can see in the above chart, [impervious] paved surfaces gave a runoff coefficient of 0.94 for the 5-year storm event. Toward the bottom of this chart, "Lawn" and "Parks/Golf Courses/Cemeteries, 8% impervious" have a runoff coefficient of 0.21.

As far as I know, there is no such coefficient for pervious concrete to be used in the Rational Method. On the one hand, it isn't really necessary, as infiltration hardscapes may make the Rational Method less necessary. Or, perhaps the Rational Method will be adapted to vet and verify successful implementations of LID measures. In the meantime, it seems that a stand-in number is necessary - what if we were to use the "Parks/Golf Courses/Cemeteries, 8% impervious" 0.21 as a reference, and then include the >0.21, as it is less then 0.21, however it is unknown how much less at this point, for research has not yet been completed.

What do you think? Is this a reasonable way to discuss the Rational Method and pervious concrete?

** The limiting factor when dealing with pervious concrete is the subbase soil’s infiltration rate. Given enough area and enough reservoir base, it is possible to infiltrate a serious storm.

To chat directly with the author of this post, you can email me at Lauren@BayAreaPerviousConcrete.com

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Sources: chart http://www.iowadot.gov/design/dmanual/04a-05.pdf
conversation and cocktail napkin - inspiration to post

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Stormwater Sleuthing - Episode 1

David Liguori went out into the field, during the last rain, to see what the stormwater runoff situation looked like in Woodside, California. Watch the video below to see what did and didn't run off!



What did you think? Do you have a Stormwater Sleuthing location (in the Bay Area) that you would like David to investigate the next time it rains? Let us know in the comments below or contact us here. Thanks!
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More Pervious Concrete in New Jersey Thanks to Assembly Member Rumana

Assembly Republican Whip Scott T. Rumana is a great advocate of pervious concrete. He spoke at a hearing of the Assembly Environment and Solid Waste Committee, encouraging New Jersey to utilize pervious concrete for "building walkways, access roads and parking lots"(Rumana, Dec. 10).

From the article:
“The bill, A-1912, would require any state agency to use pervious concrete “wherever appropriate” including access roads, pathways, roadways and parking lots. The New Jersey Department of Environmental Protection would be charged with adopting criteria for the use of pervious concrete on state projects.”

We, here at Bay Area Pervious Concrete, completely agree with State Assemblymember Rumana! By properly planning with and installing pervious concrete well will save construction costs, reduce storm water runoff and reduce storm water pollution! Contact us for more information, and please click here for the great article featuring State Assemblymember Rumana!
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We install GraniteCrete!

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Have you heard about GraniteCrete? GraniteCrete has the natural look and feel of decomposed granite or crushed rock but it holds up with the strength and durability of cementitious material. GraniteCrete is porous, and so has stormwater management and heat island benefits. We recently installed some GraniteCrete in the Golden Gate Bridge visitor area, see pictures above and below. If you have an application of GraniteCrete where you would like a certified installer to give you an estimate, contact us!

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Pervious concrete has an industry magazine!


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Check out the most recent thinking about pervious concrete across the United States with great photos, articles and advertisements from local pervious experts in your area. PerviousPro is the brainchild of Dale Fisher and the people over at the NPCPA - the National Pervious Concrete Pavement Association. We even have an article written by Bay Area Pervious Concrete's own Lauren Wray.

Check out this issue here:

http://viewer.epaperflip.com/Viewer.aspx?docid=85d951d5-33b1-47c8-b174-a05200d37fc9

Let us know what you think!

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4 Layers for Stormwater Management


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We at Bay Area Pervious Concrete have come a long way towards developing the Pervious Concrete as a viable Stormwater Management System. Going through this diagram, you can see where the water goes -- one of our most frequently asked questions.

Starting at the bottom-SOIL
We do soil infiltration tests before our jobs so we can understand how fast the water will soak in, underneath the pervious concrete. Once we understand the infiltration rates and soil composition, we can engineer the appropriate depths to excavate for the next layer, the drain rock.

Before we lay the drain rock we sometimes will lay a layer of GEOTECH Fabric, which adds a helpful barrier against some less porous soil types. We determine the need for this during the soil composition and infiltration tests.

Now for the DRAIN ROCK!
Drain rock is laid several to many inches thick, depending on the rain event to be captured, the soil type below, and how much impervious surface is draining into this slab. It is a very specific type of drain rock, not the typical base used under concrete which is impervious - we want to maintain about 40% air space to both allow water to pass through and give it place to "hang out" if the soil has a slow infiltration rate.

Finally the PERVIOUS CONCRETE
The pervious concrete is then laid on top of the drain rock, screeded and rolled into place and covered in plastic, where it will cure for at least a week.
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Redwood Avenue - Driveway

The Situation:
The client had flooding in the back and front of the house due to an uneven grade of the lot and excessive roof runoff.

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Why Pervious Concrete?
He initially wanted a pervious concrete driveway because of impervious ground cover limitations in his city.

The Solution:
We designed a pervious concrete driveway and side yard that is also the retention pond for all of the roof and yard runoff.The pervious concrete water retention system captures 100% of their runoff from the roof AND the lot. They now have a dry front yard, back yard and they can grill just off the kitchen without puddles!

redwood-after1redwood side yard after
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