Top navigation

 

The Art of Integrating Rainwater

by Steven Torgerson

Many of us plan a portion of each day based on rainwater. In my house, we often ask the question, “Is it going to rain today?” before we select our attire or decide our activities. Earlier this month, my daughters asked if we could go to an outdoor pool early next week, and I responded, “We can—if it isn’t raining.” Precipitation from storm events allows the world’s population to survive and thrive. Rain supports the crops that we eat and the water that we drink. Rain can be at once a precious resource and a damaging event; it can be gentle and life-giving one moment, and then powerful and destructive the next.

My daughters prepare for the next rain event. Photo Steven Torgerson

As rainfall intensity increases, the water on the ground picks up velocity that can carve out ravines, transporting sediment that can choke out life in our rivers and oceans. As it flows, it can drag along with it contaminants, such as phosphorous and nitrogen, which pollute drinking water; this polluted water then kills wildlife and can grossly alter the flora-fauna balance in local ecosystems. Large rainwater events can cause significant structural damage to our homes, businesses, roads, public infrastructure, and, ultimately, to the heart and spirit of our communities. In recognition of this danger to plant, animal, and human welfare, the United States Environmental Protection Agency now formally codifies stewardship over this rainwater runoff, categorizing it as “stormwater management” and regulates it as part of the Clean Water Act.

Outfall during a large storm event. Photo: Steven Torgerson

Rainwater is a natural part of the earth’s ecological system. We are powerless to produce it or to make it stop. When, where, and how much rain comes is entirely (and frustratingly) out of our control; however, as design practitioners, we can help direct what happens to that rain once it hits the earth. We are asked to plan for it as part of regulations, as well as health, safety, and welfare standards. Since we are powerless to control the rain itself, we must instead control the way that water moves through the places we design. And as designers, we try to mimic nature by using proven best management practices to capture, store, and infiltrate rainfall.

Blending Function and Beauty

In my practice of designing stormwater solutions over the past decade, I have seen hundreds of implemented projects throughout the Mid-Atlantic region. These stormwater management solutions are often unsightly “holes” in the landscape, and many of them seem like an afterthought, a nuisance that must be dealt with to meet code. They are places that people do not want to visit and that the maintenance staff and owners despise. These spaces are often considered the “cheap” land at the bottom of the site. The objective has often been to make them functionally work as an engineered practice and then belatedly hope that they will become a desirable and aesthetically pleasing place. The fact is that, with proper planning, collaboration, and understanding, another—and better—alternative is available. The very landscapes where we live, work, and play can harmoniously capture, hold, and infiltrate that rainwater. Beauty can also be functional. Brookside Gardens is an example of how to create such a landscape.

Illustrative Site Plan for Brookside Gardens. Image Courtesy of Steven Torgerson & Ching-Fang Chin

Located in Montgomery County, Maryland, Brookside Gardens is an award-winning, 50-acre public garden with a mission to “foster an appreciation for the art of gardening and the science of horticulture through plant collections and displays, learning opportunities, and special events.” AMT Landscape Architecture + Design Division collaborated with the Maryland National Capital Planning Commission’s project manager, Ching-Fang Chin, PLA, to design and permit the first two phases of the 13-phase masterplan for the Gardens. The vision for the project was to support the garden’s stated mission, create a front entry and parking experience that evoked a garden, allow for safe pedestrian access, and develop flexible public spaces that could accommodate intimate discussions and larger gatherings—all while also incorporating rainwater into the design aesthetic. To achieve this last element of the vision for the project, we focused on how to capture, store, and infiltrate precipitation seamlessly into the site design. Following are the winning strategies that we used to achieve this goal.

Blending Function and Beauty

In my practice of designing stormwater solutions over the past decade, I have seen hundreds of implemented projects throughout the Mid-Atlantic region. These stormwater management solutions are often unsightly“holes” in the landscape, and many of them seem like an afterthought, a nuisance that must be dealt with to meet code. They are places that people do not want to visit and that the maintenance staff and owners despise. These spaces are often considered the “cheap” land at the bottom of the site. The objective has often been to make them functionally work as an engineered practice and then belatedly hope that they will become a desirable and aesthetically pleasing place. The fact is that, with proper planning, collaboration, and understanding, another—and better—alternative is available. The very landscapes where we live, work, and play can harmoniously capture, hold, and infiltrate that rainwater. Beauty can also be functional. Brookside Gardens is an example of how to create such a landscape.

Located in Montgomery County, Maryland, Brookside Gardens is an award-winning, 50-acre public garden with a mission to “foster an appreciation for the art of gardening and the science of horticulture through plant collections and displays, learning opportunities, and special events.” AMT Landscape Architecture + Design Division collaborated with the Maryland National Capital Planning Commission’s project manager, Ching-Fang Chin, PLA, to design and permit the first two phases of the 13-phase masterplan for the Gardens. The vision for the project was to support the garden’s stated mission, create a front entry and parking experience that evoked a garden, allow for safe pedestrian access, and develop flexible public spaces that could accommodate intimate discussions and larger gatherings—all while also incorporating rainwater into the design aesthetic. To achieve this last element of the vision for the project, we focused on how to capture, store, and infiltrate precipitation seamlessly into the site design. Following are the winning strategies that we used to achieve this goal.

Designers mimic nature by using the the concepts of capturing, storing, and infiltrating precipitation. Image Courtesy of Steven Torgerson

Design for Rain

From the start of the project, we knew our plan needed to accommodate water through the site; this part of Maryland routinely receives just over 40-inches of annual rainfall, and we recognized that the rain would come regardless of whether or not we designed for it…so we’d better design for it. We used schematic sections to test the feasibility of each alternative and often found that the design would not work. For example, parallel to the main entry, we considered using an infiltration berm that would capture the water before flowing off the site and into the stream. After cutting a quick section, it became clear that we would not be able to integrate the berm into the landscape without disturbing the critical root zones of the trees we were saving. To better use the site, we incorporated permeable pavement that allows for both parking and stormwater to be captured and infiltrated into the ground below.

Installing permeable pavers in the parking lot. Photo: Steven Torgerson

Dream Big

As we worked through the design process, we thought about almost every green infrastructure tool that we knew about and how it could be incorporated into the site design. Our justification was easy as it supported the mission of teaching visitors about how to integrate rain into the landscape. We integrated shortened parking spaces, rain gardens, bioretention, bioswales, permeable pavement, conveyance swales, living walls, and cisterns into the design. We extended the phytoremediation to blend seamlessly into the rest of the planting design. We also used different planting zones to accommodate varying levels of soil moisture. One example of dreaming big during the planning was the integration of the cistern. Our vision was to take water from the roof of the existing building and use it in the water wall on the lower end of the site. This portion of the design ended up being value-engineered during the construction process. The cost of the cistern and pretreatment systems exceeded the overall budget for the project. Although it was difficult to see this portion of the design disappear, our willingness to dream big ensured that other essential design elements remained as part of the garden and visitor experience.

The bioswale with the black locust bridge was one of the design elements that we were able to keep through dreaming big. Photo: Max Kantzer

Collaborate with your Engineer

At Brookside Gardens, we had the benefit of collaborating with our in-house engineers on the project. Through trial and error, we have found that the best way to work with our engineers is to communicate so that we understand what goals they are trying to achieve to meet the stormwater regulations on the site. Once we know what they are trying to accomplish, we can then work with them to achieve these goals in a manner that also embraces a design aesthetic that is consistent with the rest of the site. At Brookside Gardens, we worked closely with our engineers on ways to integrate stormwater management solutions that were both functionally and aesthetically appropriate, often going back and forth with questions and brainstorming when they would recommend a solution that would not work with the site design. This process of open communication and collaboration with our engineers allowed us to come up with solutions that would meet code requirements for stormwater management and integrate virtually seamlessly into the overall design aesthetic and experience that we were seeking to create.

The process of installing a microbioretention in the parking lot. Notice the side slopes are greater than 3:1. Photo: Steven Torgerson

Understand the Tools

Regulatory agencies have already developed the tools that they will accept to treat stormwater on the site. Reviewers have a checklist that they use to check whether a stormwater design meets the minimum requirements. By understanding the language that they use and the tools that are acceptable, we were able to knowledgeably and creatively integrate rainwater into the site. For instance, when we shortened the parking spaces by 1.5-feet and used a shorted curb as the wheel stop, we were able to reduce the water-impervious surface area of the parking lot that would have otherwise needed to be treated for stormwater management. To get the reviewers to accept this solution, we showed the end of the parking lot behind the shortened curb as planted parking. By integrating the shorter bays into the design, we were able to reduce the amount of impermeable surface in the parking lot by almost 2230 square feet, which in turn reduced the total amount of treatment required for the site.

Address Conveyance

There are two ways that rainwater moves through a design site; either it falls directly on the site or it flows down onto the site from a higher elevation. Both of these avenues of rainwater movement must be addressed in the site design. At Brookside Gardens, we had steep slopes along the upper portion of the site that ended at the parking lot. The design called for this off-site water to be routed around the parking lot and into the adjacent amenity pond through the use of conveyance swales. During the construction process, the contractor did not install and stabilize the swales per the design. Then, during a subsequent storm event, the water jumped the erosion control measures and dumped massive amounts of sediment into the permeable pavements. After this incident, the contractor went back and installed the swales per our design, and this solution has worked perfectly ever since. On another area of the site, there is a natural vernal pool and spring that feeds into the amenity pond. We used the vernal pool as an amenity and integrated a boardwalk network to allow pedestrians to safely access the site, creating a new garden experience, and protecting the natural resources.

Boardwalk over the vernal pool. The boardwalk was installed using Diamond Piers to minimize disturbance to the environmentally sensitive areas. Photo: Steven Torgerson

Although each site is different, there is room for practitioners and designers to creatively push the bounds of rainwater integration into our site designs. Ultimately, we are creating spaces in which people will live, work, and play; however, these are also spaces that will receive rainfall, whether we have designed to accommodate it or not. By designing for rain, dreaming big, collaborating with our engineers, understanding the tools, and addressing conveyance, we can seize this opportunity to create spaces that people love and that respect the power of Nature. Our role can make the difference between another despised hole in the landscape and a home for both people and the environment.

The Gateway Plaza…a loved space at Brookside Gardens. Photo: Angela Marchetti

About the Author

Steven Torgerson is a Registered Landscape Architect and the Director of Landscape  Architecture + Design Division at AMT. He has nationwide experience in planning and design within an ecologically resilient framework and is passionate about creating spaces that are catalyst for people to interact with their environment and community. Mr. Torgerson’s multidisciplinary design approach encourages alternative solutions to complex rainwater problems. He delights in community engagement and the opportunity to integrate public preferences into the design outcome. Before coming to AMT, Steve served as the Cultural Landscape Architect at Yosemite National Park and was the lead landscape architect for the Forest Service during the 2002 Winter Olympics. He has won numerous awards for his work in landscape architecture, including the 2018 ASLA Potomac Chapter Honor Award for Brookside Gardens and the 2017 ASLA, Potomac Chapter Honor Award for Greening DC’s Streetscapes. Mr. Torgerson holds a Master in Landscape Architecture from The Pennsylvania State University with an emphasis in watershed planning and a Bachelor of Landscape Architecture from Utah State University.

***

Each author appearing herein retains original copyright. Right to reproduce or disseminate all material herein, including to Columbia University Library’s CAUSEWAY Project, is otherwise reserved by ELA. Please contact ELA for permission to reprint.

Mention of products is not intended to constitute endorsement. Opinions expressed in this newsletter article do not necessarily represent those of ELA’s directors, staff, or members. 

ELA