New Public LID Projects for Tulsa, Norman

Part of the American Recovery and and Reinvestment Act of 2009 (ARRA) included provisions for clean water projects in Oklahoma. All in all, Oklahoma was granted access to $31,662,100 in funds to improve water quality within the state. One of the stipulations of the ARRA is that 20% of these funds, or about $6.3MM, be used for "green" infrastructure projects.


Three projects that have been funded as part of the "green reserve" are an experimental green roof at the National Weather Center in Norman, Oklahoma, redevelopment of the dry pools into roof gardens at the downtown Tulsa City/County Library, and development of raingardens at the Tulsa City/County Library location in Sperry.



At the National Weather Center, a section of roof has been set apart for installation of a green roof system. The purpose of this roof section, as with many aspects of the NWC, is to educate the public. According the Oklahoma Water Resources Board, "Wide spread adoption of green roof technology remains absent in Oklahoma due to a limited local knowledge. This roof will be the first step to correct market deficiencies through knowledge creation and dissemination."


At the Tulsa City/County downtown library, we've all seen the "reflecting pools" located south of the library in the roof of the parking garage. The pools have been dry for as long as I can remember due to maintenance and structural issues and are something of an embarrassment, considering their location next to the Convention Center. The new green roof garden will be an asset and far more aesthetically pleasing.



The last LID project currently funded is installation of raingardens at the Sperry library. Sperry has had significant flooding issues in the past and the library continues to have a wet spot outside the front door. Why not a raingarden? This installation should address about 50% of the runoff from the facility and provide an educational opportunity as well.

Permeable Pavement for Oklahoma

Over the past few years I've fielded a number of questions about the use of permeable pavement in Oklahoma. Permeable pavements are an alternative to conventional concrete and asphalt paving that allow for infiltration of stormwater through the pavement and into a subsurface storage area or drain. Recently, there have been some significant installations, including Chicago's U.S. Cellular Field parking lot consisting of 6 acres of interlocking pavers. Its important to look into the advantages and limitations for its use on local sites.

Initially, I began by looking into the ratings for permeable pavement provided by the EPA. EPA showed permeable pavements to have a failure rate of about 75%1,2. That was not encouraging. I looked into the studies behind these findings and found that they were from 1992. Well, a lot has happened in the LID world since 1992, so what about more recent studies?

My inquiries took me to states like North Carolina and Georgia, where water quality regulation is intense, and to the EPA's LID Development Center in Portland, Oregon. As you may know, some advantage of permeable pavement include:

* The lifespan of a northern parking lot is typically 15 years for conventional pavements due to freeze/thaw stress, which is also common in Oklahoma. Porous asphalt or concrete parking lots can have a lifespan of more than 30 years because saturation during freeze/thaw is reduced3.

* Permeable pavement transforms areas that were a source of stormwater runoff to a system that can reduce or eliminate runoff that would have been generated from traditional paving. Studies show stormwater retention rates ranging from 25-100% depending upon storm intensity. http://www.thewaterchannel.tv/index.php?option=com_hwdvideoshare&task=viewvideo&Itemid=53&video_id=349

* Permeable pavement can reduce the amount of pollutants in stormwater runoff and can address suspended solids (high removal rates), acid rain (some types effective), phosphorous (moderate removal), nitrogen (moderate removal), and metals pollution (best in vegetated systems).

So what's not to like? There are some drawbacks and limitations to use including:

* Permeable pavement is not recommended, or in some states even allowed, where surface soils are silt or clay. That's most of northeastern Oklahoma. Generally, permeable pavement is only recommended in areas with sandy surface soil, like the western part of the State, or where stormwater has been pretreated.

* Even when properly sited, maintenance requirements are critical for the success of permeable pavement. Proper maintenance includes vacuum sweeping or high-pressure water washing at regular intervals and inspections after each storm. If you can't commit to maintenance, there are better options.

* Porous pavement has reduced strength compared to conventional materials and isn't appropriate for applications with high volumes, high speeds, or heavy loads.

So how might permeable pavement be used in Oklahoma? Walkways, driveways, alleyways, and overflow parking are some options. And consideration should be given to preventing sediment from reaching the pavement, especially during construction, which can trouble a pavement system before it's even in use.

Finally, we have a responsibility to put our best foot forward for LID as these topics are being introduced in local communities, to hit the ground with practices we know have positive reproducible results. Who wants to hear, "More of my tax dollars gone to waste." again? The future of LID is in our hands!

1 Schueler, T.R., P.A. Kumble and M.A. Heraty. 1992. A Current Assessment of Urban Best Management Practices. Metropolitan Washington Council of Governments, Washington, DC.

2 J. Galli. 1992. Analysis of Urban BMP Performance and Longevity In Prince George's County, Maryland. Prepared for Department of Environmental Resources, Prince George's County, MD.

3 Gunderson, J., Pervious Pavements: New Findings About Their Functionality and Performance in Cold Climates, Stormwater, September 2008.

Canopy Economics - The Power of Trees

During a news conference seven years ago this week, American Forests (americanforests.org) unveiled one my favorite studies - it showed that urban tree deficits were costing tax payers billions of dollars each year in air and water benefits. At that point, San Antonio, Texas, Charlotte, North Carolina and San Diego, California joined in as the first cities in the nation to take action to reverse the tree loss trend by incorporating tree cover data into their infrastructure database - considering trees on the same level as roads, bridges, and treatment plants.

The connection between tree canopy and stormwater may not be immediately clear. Trees reduce the volume of stormwater runoff by capturing some rain on their leaves and branches, which then evaporates back into the atmosphere. Other water infiltrates into the soil rather than running off the land, which must be managed. For example, San Antonio’s urban forest manages 974 million cubic feet of stormwater, valued at $624 million using a $0.64 per cubic foot value based on local engineering, construction, and land costs (Pape-Dawson Engineers).

The findings from American Forests showed that San Antonio had 27 percent tree canopy, seven percent open space, 64 percent impervious/bare urban land, and one percent water. However, if tree cover were increased from 27 to 35 percent citywide, 2.5 million pounds more air pollutants would be removed each year and stormwater runoff would be reduced by 103 million cubic feet during an average 2-year, 24-hour storm event. This service would be worth an additional $200 million in avoided stormwater facility construction.

"Flooding in San Antonio is an age-old issue," said Carol Haywood, a planner with San Antonio's neighborhood and urban design department. "Most folks think we need more concrete culverts to simply whisk the water away as fast as possible. We will use this green (infrastructure) data to model and demonstrate the ability of trees to perform a similar function without adding new concrete."

For its part, the City of Tulsa began a tree planting program in 2007, after that year's devastating ice storm. For comparison, that storm destroyed or damaged as many trees as Up With Trees had planted in its entire 30 year history. Since that time over 5,000 trees have been replanted, with a goal of 20,000 trees by 2010 through ReGreen Tulsa. The City, through its Tree Advisory Oversight Committee, seeks to increase tree canopy by 3% year over year through 2013. Overall, the American Forests recommend 35% canopy coverage in urban areas.

When municipalities are looking to control long-term stormwater infrastructure costs, it should be clear that canopy cover can be a key element. What if we designed for the 2-year 24-hour event with both concrete and canopy? How much less would taxpayers have to spend? And how much more we would enjoy our new public infrastructure.

Tulsa Raingardens: The Clyde Home

This week we're featuring a local raingarden designed and installed by Tony and Jen Clyde in midtown Tulsa. I've been talking with Tony about his raingarden plans for a couple of years now. Their garden was planted in the summer of 2008, so I was curious as to how it was coming along. The answer is, "Great!", as you can see from these photos.


Tony designed this raingarden to address runoff from one section of their home encompassing about 170 square feet of roof. The location sits off the southwest corner of the home, in full sun, and is just off a stone sitting area. To begin his garden design, Tony performed a permeability test at the proposed raingarden location and found he had loamy soil with good infiltration.



The roof section selected for this garden has two downspouts that were disconnected from the storm sewer and rerouted, as shown in these photos. The first shows the downspout connection. The second photo shows the inlet into the raingarden.


Tony then began to dig out the raingarden. He excavated about 1.5 cubic yards of dirt, which has since been used in other yard projects. The garden is kidney-shaped, measuring about 4.5' x 10', or 45 square feet, and is 6" deep.


As an overflow outlet, a rut left by a utility truck was purposefully not filled in. The rut is barely noticeable in the grassy yard but functions regardless, channelling water out of the raingarden and into the street (and storm sewer) during high rainfall events. The overflow is located in the bottom left corner of this photo. Every raingarden needs an overflow.


The garden was then planted with facultative wetland plants - that is, plants that can handle periodic flooding. For this garden, Tony selected swamp milkweed, swamp verbena, sawtooth sunflower, and leadplant. The plants were obtained from Pine Ridge Gardens in Arkansas, which specializes in native plant materials. The plants were shipped directly to his home and cost about $110. To finish it off, Tony selected a good cypress mulch.

When I visited, there were numerous different species of butterflies and bees present. Although the plants were not chosen to attract pollinators, it is certainly effective. The garden looks like a natural, but planned, part of the landscape.

I asked Tony about comments from neighbors. He said the most common have been regarding the garden's attractiveness. But he did tell about one visitor who remarked, "You know your pond doesn't hold water." Some things take a while to catch on. :)

Dealing with Off-site Runoff

I remember the first big storm that occurred after we moved into our current home: a river carved its way under the fence and through the newly sodded backyard. Where did it come from? A peek over the fence showed me something I hadn't noticed before. The adjacent backyard was a concrete slab, funnelling runoff from the house, outbuildings, and pavement through our yard. Granted, it wasn't my neighbor's fault. The problem had been there for decades and they inherited it just like us.

A number of people have similar experiences, though, when neighbors add on or developers substitute McMansions for bungalows. New guidance being developed by the City should address some of those infill issues, but what can you do about "run-on" short of legal action? In this case we looked at redirecting the river and decreasing its energy. And the application may give you ideas about how to handle your own off-site problem.

First, we talked with our neighbors about what we were observing. They made some changes to their yard, including switching two parking spaces to loose gravel. Tremendous! And it looks great too.

On our side of the fence, we used recycled concrete, which came from tearing out our own paved yard, to provide energy dissipation for the flow entering from the fenceline. Basically, that means putting something in the way of the stream to smack it around and is provided by the larger stone in the middle of the garden to the left. We then used the same materials to edge a planting bed along the fence and provided spaces between the concrete to allow water flow. The water then enters a horizontal gravel filter, made up of river rock, which dissipates the flow further and allows it to pass through the yard without being seen. The filter also acts as a walkway from the house to the play yard. On the downstream side of the walkway, I added a raingarden that is a few inches lower than the gravel bed.

Overall, the system dissipates the energy of the water entering the yard, filters the water, conveys it, and provides some infiltration. Afterwards, water exits into the alley. During high rainfall events, water flows through this system as well as overflows to the yard and a shallow lined channel directly to the alley.

I mentioned the design to someone recently and they asked "Isn't that just a walkway?" And I thought, "Yes, and No." I'll highlight again that stormwater controls don't have to look different, they just have to work different. And if it is mistaken for a walkway, great. That tells me its a job well done.

What's Up With Rats?

It seems each time I talk about raingardens, someone has to ask about vermin. You know, squirrels without the cute fuzzy tails: rats and mice. The question is usually, "Do raingardens bring in vermin?". My standard answer is, "No". But after hearing it so many times, I decided to get some additional advice on the topic.

I talked with both a horticulturist and a biologist about this question. On my list were Jay Ross, Horticulture Curator at the Tulsa Zoo, and Stephanie Rainwater, a biologist at URS. Jay and Stephanie both noted that any garden with dense vegetation can provide a nesting area for all types of critters, from songbirds to cats to, you know. The key to what critters you attract is what food supply is nearby. If you have insects, you should get birds that eat insects, and so on.

In the public arena, a community might consider whether the garden is located near areas of animal feeding (advised or not), such as a duck pond or petting zoo. Likewise the residential homeowner should consider whether they leave dog, cat, or bird food where other animals can access it. In my own yard, I've found the compost heap to be a problem.

But are there features that make raingardens uniquely less prone to being used by vermin than other landscaping? The answer is yes. Raingardens are designed to flood - every time it rains. There aren't a lot of critters that will put up with being flooded on a regular basis - they'll pick somewhere else to nest.

So, what does all this mean? Raingardens should be less likely to house these unwanted guests than other types of gardens and landscaping, a fact that should encourage others to bring stormwater controls into their landscaping.

Rainwater Harvesting: How Much is Enough?

This week's poll has to do with what people want to use rainwater collection for, whether it be watering lawns or running the commode. Even ambitious LIDers won't be using rainwater to wash clothes anytime soon b/c they don't have dual plumbing systems (potable/non-potable) in their homes. So that leaves most us looking at outside uses, watering the lawn and the like.

Rain barrels are becoming more and more popular. But it seems the minute most people put one in they want it bigger: a 55-gallon barrel doesn't go very far. How far you might ask? Well, I use a 55-gallon barrel for air conditioner condensate collection and am able to water my container plants for about week from one barrel. How much water do you need?

A traditional lawn needs about 1-inch of water per week during the summer. That's 0.623 gallons per week per square foot. (Sometimes I just call it a half-gallon per foot to make it easy.) If you have a lawn that is 20' x 50', that's 1,000 square feet of lawn. It would take 623 gallons of water per week. During the summer, let's say that it doesn't rain for a month. Over those four weeks your lawn would need 4 x 623 gallons = 2,480 gallons. If your lawn is bigger, you'll need more, maybe much more!

So, here's where reason kicks in. Are you ready for a 2,500 gallon (or larger) tank? Do you have the space? (A 2,500 gallon-tank is about 8 feet in diameter and 7 feet tall.) Does your neighborhood allow these kinds of appurtenances?

There are a number of factors to consider when evaluating "How Much is Enough?". Maybe for you it is a rain barrel to refill the fish pond, maybe it's finding out if the old cistern in the backyard still holds water, or maybe its having a system engineered for your specific needs. Whatever you decide, there's an opportunity every time the rain falls.