“Let it Rain” — a raingarden project in Central Ohio
(from an engineer’s perspective)
Joseph C. Tribble; PE, CPESC
Stormwater Consultants, LLC
I was fortunate to have had the recent opportunity to work on a raingarden design and installation project with Amy Dutt, of Urban Wild, and members of the First Unitarian Universalist (First UU) Church of Columbus (Ohio). Both Amy and I donated much time and effort on this project, but members of the church donated a good deal of time and effort as well. In addition, they gave us trust and patience — and that was very much appreciated. Without that, the efforts of Amy and myself would have been much more difficult. There were many other contributors on this project and they are mentioned below.
Raingardens – a new stormwater management tool
After over two decades of designing subdivisions, commercial sites and roadways in central Ohio, I thought I had mastered the art of stormwater management design. Paving the landscape and piping the runoff, with a little detention (to slow flowrates down a bit) and some treatment (to remove a few pollutants) had always been a good recipe. It was fast and efficient — and getting stormwater to the rivers as quickly as possible, after all, had always been the main goal. A little erosion, especially where no one would notice, wasn’t going to hurt anything, and, if it did, we could always just add a little more rock channel protection.
It took a while for the raingarden concept to catch on with me. At first, I wasn’t too impressed with the “landscaped holes in the ground” that didn’t drain anywhere. I couldn’t envision how they would be anything more than a mere “drop in the bucket” in the overall stormwater management scheme. But, I humored my raingarden friends and, in the process, began to come around. Maybe draining stormwater into a system of “engineered” filters could remove pollutants as effectively as conventional methods. Maybe giving stormwater an opportunity to recharge the groundwater system (reducing nuisance flooding and hard costs along the way) might be beneficial as well. If we put some thought and effort into this concept, maybe raingardens could become an effective tool to manage runoff, pollution and construction costs. It could be a win-win-win scenario.
When you get down to it, raingardens are nothing more than “sexy” bioretention filters (engineered depressions that treat first-flush runoff and allow managed infiltration) anyway. But, that sexy part of raingardens (ornamental plants, dry streams, etc.) is important. In order for them to catch on as a mainstream stormwater management tool, they have to provide aesthetic appeal. Equally important, however, is the ability to get them designed and constructed efficiently. If the design-build community could find ways to aesthetically, efficiently and cost-effectively incorporate raingardens (in lieu of traditional landscaping) into site-scapes, we might be able to use them to make a positive difference in “stormwater sustainability”.
A Raingarden Opportunity
In March 2009, when Heather Dean of FLOW (Friends of the Lower Olentangy Watershed) and I became aware of grants, from MillerCoors and River Network, to create sustainability demonstration projects, we jumped at the opportunity to create a raingarden project in the Olentangy River watershed — and we knew just the place to do it. Through another endeavor, we had become familiar with the First UU Church in the Clintonville area. They were good neighbors in the community, interested in environmental stewardship and, best of all, had a property that would allow a great demonstration raingarden to be installed. With the help of Amy Dutt, Heather partnered with First UU, prepared a winning proposal (complete with a project budget and concept plan) and received one of the MillerCoors/River Network grants. The concept plan included a stone wall and native plant material, both of which matched the surrounding landscaping, and a decorative “dry stream”. Winning this proposal was exciting for me. I’d be able to work with Amy, participate in the design and construction process — and see this raingarden concept develop first-hand.
Although I was familiar with raingardens, I had never been involved in the design or construction of one before. A successful proposal and a concept plan were a good start, but there was also the issue of making it work — and trying to get it constructed before winter. Those issues made me a little nervous. This project would require retrofitting an existing roof drainage/storm piping system and those types of projects did not always go smoothly. I didn’t know it at the time, but building this raingarden was going to require a monumental effort on the part of the church and the design team — and significant coordination and cooperation with the City of Columbus, Columbia Gas, Igel Construction and others. I didn’t know it at the time, but building this raingarden was going to be an educational experience.
The location of the raingarden was a given. The green space on the north side of the First UU property had been a perfect spot from the beginning. Rainwater from the roof area was convenient, the location was highly visible to surrounding streets and there was plenty of unencumbered area (or so we thought) to work in. Our first assignment, however, was to determine the size of the raingarden. Although there are easy equations to compute raingarden size, this calculation wasn’t that straightforward. The configuration of the existing roof and pipe system(s) created a scenario where, if designed conventionally, we would have had either a very small garden (serving only a small part of the roof area) or a very large and expensive garden (serving the much larger roof area). Neither option was consistent with our project goals and budget.
We settled on a unique design. Our approach was to construct a manageably-sized raingarden and take the entire roof area to it, but incorporate two major deviations from conventional raingarden designs. The first deviation was to inlet stormwater from the roof and pipe system into a sub-surface aggregate trench, immediately below and integral with the dry stream. This gave us some much-needed elevation difference and would allow diffusion of the concentrated pipe system flows, keeping them from eroding the raingarden surface during heavier rains. The second deviation was to provide an overflow device (in an existing upstream manhole) that would allow excess roof runoff to bypass the raingarden when it reached capacity during storms that produced more rain volume than it could handle. This would keep the raingarden from being “flooded out” on a regular basis. Both of these deviations allowed us to treat the larger amount of roof area while protecting the raingarden as well. I hope these concepts can serve as a model for future projects (Raingarden System Schematic).
With our unique design approach in hand, the next task was to get City of Columbus approval of our concept, including the required modification to the existing sewer plan for the property. As many will attest, modifying an existing plan, even without a unique design approach, was normally a time-consuming process. In this case, however, working with the City could not have been easier. With the sustainability effort in mind, they took the time to understand what we were trying to accomplish — and worked with us as we obtained the necessary construction permit. The only major requirement was that we use a licensed contractor to retrofit the existing system. The City’s final and biggest help, however, was waiving the $2000 inspection fee. Without that, starting the project may have not been possible.
Raingarden Retrofitting — expect the unexpected
Retrofitting anything, especially when it’s old and background information is sketchy, can be a challenge. Our First UU Raingarden project would certainly prove that to be true. Before construction, we were aware that there would be conflicts with an existing irrigation system, but we had no idea that a 20-year-old gas service line would become our main roadblock. One of our project partners, Greenworks Ecological, was scheduled to begin garden excavation, but they had not been on the job thirty minutes before the discovery of the line in our work area brought everything to a complete halt. As it turns out, the gas service line had been constructed improperly, which had made it impossible to locate prior to beginning work. Regardless, a muddy mess had been created in a very visible location and we were stopped dead in our tracks. We knew people at the City who could help us with our plan approval, but finding someone to work with at the gas company was another matter.
I can’t say enough about the effort Amy Dutt put forth in making the First UU Raingarden project a reality. In addition to donating her time for design and installation project management, she worked tirelessly to stay on top of, and resolve, any problems that arose. Amy’s work with gas company representatives paid off almost immediately. Columbia Gas became a willing partner in our project, relocating the gas service in a very timely manner and at no cost to us. Without that, continuing the project may not have been possible.
With the gas service relocation completed, we were left with one last hurdle — finding a licensed contractor to retrofit the existing manhole with the bypass device and construct the new pipe system to the garden. Once again, Amy came through. She contacted her friend Joe Igel, who graciously volunteered his company to help us out. Igel Construction completed this last piece of the raingarden infrastructure, along with some of the remaining site grading, and did so in a timely and professional manner as well. As before, this work was done at no cost to the project, allowing us to complete it within our grant budget.
Having completed the raingarden infrastructure, all that remained now was installation of the interior stone wall, dry stream and raingarden plants. For a “normal” raingarden, this step would have been major, but, for us, it was no big deal. We had already overcome several hurdles and were now in the home stretch. The raingarden gods, however, weren’t finished with our project yet — not without sending a little rain our way. Ironic, don’t you think, that, after all that effort, we could not complete the last step because the ground surface was too wet.
Being a part of the First UU Raingarden project was a great experience — not only from the knowledge I gained, but from the people I had the opportunity to work with. I was surprised at the level of cooperation we received from many parties. Cooperation that, in this economy, was unexpected. Although we were successful, I caution anyone who wants to retrofit a raingarden into any existing system. Expect the unexpected — and allow for time delays and additional costs. “Stuff Happens”!!!
With that said, I’m convinced that raingardens can have a prominent place in existing system and new-build stormwater management. For new-builds, raingarden networks, if properly planned at the beginning of a project, can be a very useful tool. As with conventional designs, however, they must be strategically placed on, and interfaced with other elements of, the site. Raingardens are not appropriate in all soil situations, should be kept away from building foundations, basements and heavily-trafficked or heavily-loaded areas and, as with other stormwater management methods, should be designed to consider and avoid water back-up and freeze-thaw issues. With these precautions in mind, however, raingardens, can, in my opinion, become a viable stormwater management tool.
After over two decades, it is possible to learn something new.
© 2005 – 2014 FLOW all rights reserved.