The Field

by David Hopman, ASLA, PLA

On August 12, 2018, I attended a meeting of a new committee created by the Environmental Water Research Institute (EWRI) of the American Society of Civil Engineers (ASCE). The task force, comprised of approximately 40 stormwater professionals, is titled: ASLA/EWRI Committee on Plants and Soils Performance in Green Stormwater Infrastructure (GSI). The committee will produce recommendations over the next few years that will be distributed in a booklet and online. This work will be specifically focused on providing better research-based guidelines for soil performance and plant performance as an overlapping, interrelated system rather than as individualized elements. The committee’s goal is to provide guidance on short-term, medium-, and long-term practices to ensure that systems maximize performance.

Additionally, other sub areas such as biodiversity, maintenance, and soil microbial functions will be considered. The landscape architects on the taskforce will take the lead in addressing aesthetics and other social parameters that can support or impede acceptance of Green Infrastructure as an important component of place making.

The first phase of the task force’s efforts is to create an annotated bibliography as an indicator of where research is headed and to reveal significant gaps that should be addressed. The literature review phase is being organized by Harris Trobman, Project Specialist in Green Infrastructure at the Center for Sustainable Development and Resilience, The University of District of Columbia. The committee needs good research-based literature, especially as it relates to the performance of plants in green infrastructure. If you have a favorite book or article that you would like to share, please send it to me by December 1, 2018, and I will format it for inclusion in the bibliography. Currently, the bibliography is reflective of the vast preponderance of research that has traditionally come from engineers and scientists. Please free to contact me with questions and/or comments as well. If you would like to format the citation yourself, I can send an example.

Below is some language from the committee proposal written by Neil Weinstein, ASLA, committee chair and the Executive Director of The Low Impact Development Center, Inc., and others. The prose outlines committee priorities and may help in the selection of appropriate literature:

“A considerable amount of research has been conducted related to the performance of these GSI practices with respect to pollutant removal, especially nutrients and sediment. Much of the research has focused on the composition of the bioretention soil media in an attempt to improve pollutant removal. As a consequence we have seen a developing trend towards the use of various additives to the soil media, such as water treatment residuals, and other specialty media. In addition, we have observed an increasing trend in the use of high flow media (HFM) used primarily in proprietary filtering systems. These systems typically use a mix of sand and peat moss to produce rapid flow systems that serve to reduce the footprint of the treatment facility. More recently, some research has been directed towards the operation and maintenance (O&M) requirements of these systems.

Surprisingly, we have witnessed very little research related to plant performance and survivability. This is understandable since most of the research has been conducted by engineers whose primary focus is water quality performance. However, with the increasing use of these GSI practices and in particular the use of these practices as a component of green streets designs which incorporate curbside bioretention and rain garden systems, the plant materials are being placed in relatively harsh climatic conditions. At this time, we have very little information related to which of the numerous native species available for use perform best and survive under these conditions. This type of information could be very useful to system designers in selecting the most effective plant materials for different type of climatic conditions. In addition, there is a growing realization that some plants are better suited than others to provide uptake and removal of toxic materials, but this type of information is currently not readily available to bioretention designers…

…It is important that both quality soil and vegetation be viewed together as an essential part of a dynamic system used to control stormwater quantity and quality. These practices can mirror natural systems that over time can improve the chemical, biological, and physical properties of soils and allow for improved plant growth. As vegetation grows, it accumulates more organic matter, which can help to increase performance of the practices over time. Proper management of the plant materials and the soils is an important part of this relationship that is currently not being applied.”

International Low Impact Development Conference in Nashville, Tennessee, August 12-15, 2018

After the committee meeting, I participated in the International Low Impact Development Conference in Nashville, sponsored by EWRI. It is very heartening to see the interest in plants that was expressed throughout the conference by the 600 attendees, especially at the session where I presented a short talk on polycultures in Green Infrastructure and answered questions as part of a panel organized by Meredith Upchurch, PE, ASLA. The session was titled “Soils and Plant Symbiosis Considerations in Green Infrastructure Design, Operations and Maintenance, and Life Cycle.” Ann English, RLA, ASLA, LEED AP BD+C, Harris Trobman, and Heather Ambrose were also featured on the panel.

The committee mentioned above is an opportunity to turn the interest expressed for softer biologically-based stormwater solutions by engineers at the conference into more effective tools that both engineers and landscape architects can utilize.

The LID Conference occurs every two years and is certainly worthwhile for any landscape architect seeking the latest thinking on green infrastructure. Of particular interest to landscape architects are the sessions where people with decades of experience with Green Infrastructure discuss their lessons learned. The Washington, DC-Maryland area, Denver, Colorado area, and Portland and Seattle areas were especially well represented in this regard.

We also had a chance to tour some of the GI in the burgeoning city of Nashville. Kim Hawkins, ASLA, principal with Hawkins Partners, Inc. in Nashville, led the charge. Figure 2 shows Hawkins Partners’ design of Deaderick Street, Tennessee’s first ‘green street,’ completed in 2009. This important connection from the State House to the Nashville Metro Courthouse and public square features permeable concrete between tree wells (inset in figure 2), stormwater planters at “bulbouts” (figure 3), 102 shade trees, and many other sustainable features that were new to the Nashville area. The stormwater planters divert approximately 1.2 million gallons of water per year from the Cumberland River.

I look forward to hearing from you and to seeing your literature suggestions. More information will follow as the joint ASLA/ASCE committee continues its work.

David Hopman, ASLA, PLA, is an Associate Professor of Landscape Architecture at The University of Texas at Arlington, a registered landscape architect, and a research associate at The Botanical Research Institute of Texas (BRIT). He is also a member of Environmental Water Research Institute (EWRI) and serves on the joint ASCE/ASLA Committee on Plants and Soils Performance in Green Stormwater Infrastructure.