Tool Helps Cities Use Trees for Stormwater Mgmt

OKI, US Forest Service and Partners Launch Site to Help Decision Makers

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Phillip Rodbell is program leader for the USDA Forest Service Urban and Community Forestry’s Northeast Region with offices at Newtown Square, Pa.

Larry Wiseman is an urban forestry consultant for Centerline Strategy in Washington, D.C.

David Rutter is senior environmental planner for the Ohio Kentucky Indiana Regional Council of Governments (OKI), based in Cincinnati.

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Posted: Wednesday, February 14, 2018 2:24 pm

Communities wrestling with critical stormwater management issues have a new tool to help local decision makers throughout the U.S. integrate trees into facility design regulations and policies for new and retro-fitted installations. developed by the Ohio Kentucky Indiana Regional Council of Governments (OKI), the USDA Forest Service and other national partners, was created specifically to help overcome the widespread lack of understanding, acceptance and credibility of using trees for green infrastructure to manage stormwater.

The site includes a document builder, hundreds of case studies, videos, methods and best practices, benefit calculators and other tools on how adding trees can boost overall system performance, often at lower costs.

Phillip Rodbell, program leader for the Forest Service Urban and Community Forestry’s Northeast Region with offices at Newtown Square, Pa., said that OKI had been dealing with stormwater issues in a big way throughout its territory and approached the Forest Service in 2015 to fund a website for its members.

“OKI wanted to capture lessons learned and share them with national groups," Rodbell said. "One thing led to another and we all agreed that the site should serve the entire country. A lot of effort went into it and we received input from many local, regional and national sources."

According to, traditional “gray” water infrastructure — concrete and metal pipes, holding tanks, pumps and water tunnels — have long supported cities and towns as they grew and developed. “However, as leaders grapple with shrinking budgets and deteriorating local infrastructure, the resilience and multi-functionality of trees and other green sites continues to broaden its appeal as a fiscally responsible investment for the long-term health and vibrancy of an area,” Rodbell said.

He noted that stormwater sewer systems are often combined with sanitary sewer lines, which can be quickly overwhelmed by storm runoff and result in combined sewer overflows (CSO), particularly with the increasing intensity of today’s storms due to climate change. “There is a sense of urgency to dealing with this problem. Larger cities are mostly located at the mouths of rivers which are seeing much larger flows from upstream due to more and more impervious development runoff, which inundates infrastructure,” he said.

Trees offer numerous benefits, according to the Penn State Extension, including:

• Canopy Interception: Working like large umbrellas intercepting and evaporating rainfall, average interception by deciduous trees can range from 700 to 1,000 gallons of rainwater annually; an evergreen can intercept 4,000 gallons. A recent Forest Service study found New York City’s street trees reduced stormwater runoff by 8,980.6 million gallons a year, with a value of $35.6 million in stormwater management costs. The average tree in New York City intercepted 1,432 gallons of rainfall every year.

• Infiltration: Trees and forests provide for infiltration into the soil to recharge groundwater. In forest soils, infiltration ranges from 10 to 18 inches an hour depending on soil composition.

• Water Consumption: Trees absorb and use tremendous amounts of water for growth and photosynthesis. A single mature oak can transpire more than 40,000 gallons of water every year.

• Pollutant Removal: Trees are very good at using nitrates, phosphates and other nutrients and removing contaminates such as heavy metals, pesticides, solvents, oils and hydrocarbons from water and soil. The process is phytoremediation. One single roadside maple is credited with removing and storing 60 mg of cadmium, 140 mg of chromium, 820 mg of nickel and 5,200 mg of lead in a single season. Philadelphia’s 25-year Green City, Clean Waters program is expected to reduce stormwater pollution entering its waterways by 85 percent.

• Stream Stabilizers: Riparian forest buffers filter stream sediment during storms, remove nitrogen and phosphorous leached from adjacent lands, stabilize stream banks, shade streams and modify their temperatures, provide aquatic and wildlife habitats and reduce velocity and downstream flooding.

Green infrastructure can also help to alleviate increasing regulatory pressure. “Many still misunderstand the full benefit of trees," Rodbell said. "Most think only about air quality and shade." He said a study to determine the impact of EPA regulations on Philadelphia determined that the value of trees and green infrastructure was significant. Not only did they help the city meet stricter regulations, but the trees also helped enhance the quality of life for citizens.

The National Pollutant Discharge Elimination System (NPDES) under the Clean Water Act is the primary federal vehicle regulating the quality of U.S. water bodies. It was developed initially to reduce pollutants from industrial process wastewater and municipal sewage discharges. Congress brought stormwater control into NPDES in 1987.

EPA issued Phase 1 Stormwater Rules in 1990, requiring NPDES permits for operators of municipal separate storm sewer systems (MS4s) serving populations of over 100,000 and for runoff associated with industry, including construction sites five acres and larger. In 1999, EPA issued its Phase II Stormwater Rule to expand requirements to small MS4s and construction sites between one and five acres.

According to the National Research Council, America’s stormwater program “has suffered from poor accountability and uncertain effectiveness at improving the quality of the nation’s waters.” One reason is that EPA estimates the total number of permitees under the stormwater program at any one time exceeds 500,000. For comparison, there are fewer than 100,000 non-stormwater (wastewater) permits covered by the NPDES program. Thus, to manage the large number of permit holders, the stormwater program relies heavily on the use of general permits.

The National Research Council also said that although stormwater has been recognized for contributing to water quality impairment for decades, federal regulations to deal with stormwater quality have occurred only within the last 30 years. Thus, regulation is expected to grow, making trees and green infrastructure even more attractive, said Rodbell.

The Trees and Stormwater Project was made possible in part by funding from the U.S. Forest Service National Urban and Community Forestry Challenge Cost-Share Grant Program. The National Urban and Community Forestry Advisory Council (NUCFAC) sets categories for the grants based on the Ten-Year Urban Forestry Action Plan. Other key participants included the National Association of Regional Councils (NARC) the Davey Resource Group and Centerline Strategy LLC.

Urban Forestry Consultant Larry Wiseman, Centerline Strategy, Washington, D.C.; David Rutter, senior environmental planner for OKI based in Cincinnati; and members of the OKI staff were key architects of the TreesAndStormwater website.

Rutter said making the site useful nationwide was a big priority. “We relied on a national advisory committee; we were able to develop a highly detailed resources guide with more than 350 documents," he said, adding that users can create a password-protected place to gather and store all the information about their individual stormwater programs.

"Armed with all of their site data, they can easily put together white papers and other documents to make the case for buy-in of elected officials and decision makers,” he said.

Rutter said that best management practices include identifying existing trees and what benefits they provide; equating the number of trees with the number of parking spaces in a given development; retaining rather than cutting down trees in a new developments; assuring that trees have enough soil to survive to maturity; working with foresters; and coordinating tree care among all municipal departments.

Wiseman is the retired CEO of the American Forest Foundation, steward for the country’s privately owned forests, and he had access to many stakeholders, research and other government agencies. He now develops programs for all aspects of urban forestry policy and practice.

Wiseman said his involvement in the project got him "obsessed" with trees as a vital tool in stormwater management. "I think a problem is still that enough people don’t fully appreciate trees, including a lot of community planners who don’t understand the role trees play in public health,” he said.

“Using the logical Document Builder, someone can make the case to policy makers that trees are important to stormwater systems and find the tools they need to create a plan that incorporates nature,” Wiseman added. “They can also scour regulations and remove conflicts.”

Visitors who register on the site take a brief tutorial, provide some basic information about their community, and are then directed to a variety of tools that help them with understanding opportunities, tree planting, stormwater best practices, design specifications, stormwater modeling, funding sources and return on investment. They can choose and save relevant documents from the resources library, which includes data for 138 entities covering 12 regions of North America.

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