TREES.

CITYgreen computer software is helping cities heighten water quality through increased canopy cover.

Tackle Clean Water Regs

Gary Moll

In the late 1960s and early 1970s the quality of the nation's waterways was so bad that by 1972 Congress passed the Clean Water Act and launched an effort to remove pollution from the nation's waterways, bring back the fish, and make safe swimming possible.

Since the passage of the Clean Water Act, water quality has improved substantially, but the work is far from finished. In 1990 the Environmental Protection Agency (EPA) reported to Congress that one-third of U.S. waterways were impaired by stormwater runoff, which directly affects water quality.

Today the EPA's regulatory efforts continue and are directed at more and different sources of pollution. Continuing the clean-up will engage a wider audience and require more innovative approaches. Locally, cities can employ new strategies such as using trees to help clean water naturally and tying urban greening to property cost-saving incentives. AMERICAN FORESTS' CITYgreen software has been designed as a tool to help people understand how trees affect stormwater and to help them make better planning decisions.

As communities grow, urban infrastructure expands and water quality regulations tighten, and stormwater managers are faced with a difficult challenge. How can they reduce the volume and improve the quality of the water that drains from impervious (impenetrable) surfaces as it makes its way into surrounding waterways? In most cities today, almost all stormwater runs rapidly off roads, sidewalks, parking lots, rooftops, and other impervious surfaces.

The traditional engineering goal has been to move stormwater out of the community as efficiently as possible through a series of gutters, sewers, and drainage ditches. However, experience has shown that moving water quickly from one place to another creates more problems than it solves, including a drop in water quality.

A more modern approach is to move water slowly through cities, allow for infiltration on site, minimizing flooding and maintaining water quality. This shift away from built infrastructure is taking hold; EPA now recognizes nonstructural methods, such as increasing tree canopy cover for slowing stormwater runoff, as a "best management practice" (BMP).

AMERICAN FORESTS has studied the effects of trees on the urban environment for 20 years, utilizing the scientific research and engineering resources of federal agencies and academic institutions. From this research it is apparent that urban forests are indicators of the environmental quality of a community and that they provide measurable benefits, in particular: reducing stormwater flow and improving water quality. These valuable services can be calculated and translated into dollars.

Trees help manage stormwater flow by intercepting rainfall and slowing the rate at which it runs over the surface of the land and seeps into the ground. When trees are present, the flow of water is spread over a greater amount of time (time of concentration), and the impact of a storm on the facilities built to handle it at any one time is smaller.

Reducing the volume of stormwater and its peak flow reduces the size and cost of stormwater structures. By incorporating trees into a city's infrastructure, managers can build a smaller, less expensive stormwater management system.

Trees are also natural pollution filters. Their canopies, trunks, roots, and associated soil and other natural elements of the landscape filter polluted particulate matter out of the flow toward the storm sewers. Reducing the flow of stormwater reduces the amount of pollution that is washed into a drainage area. Trees use nutrients like nitrogen, phosphorus, and potassium--byproducts of urban living--which can pollute streams.

As stormwater management issues have become more complex, communities across the country have found an innovative solution and a way to fulfill regulatory requirements to improve water quality. In Garland, Texas, for example, the city established a stormwater utility in 1991 to fund stormwater management projects for improved flood control, water quality treatment, groundwater recharge, and ecological preservation projects.

The city has mapped all of its impervious surfaces so it can accurately assess the amount of stormwater flowing over a parcel. Instead of linking the stormwater fee to real estate value or charging everyone a flat fee, the property owner's fee is linked to the amount of impervious surface on his or her property and to the volume to stormwater that property generates. The more you have, the more you pay.

Garland, Texas, is expanding its stormwater formula to include information provided by AMERICAN FORESTS' CITYgreen. A recent CITYgreen analysis conducted by AMERICAN FORESTS and The Davey Tree Ex[pert Company showed the value of the city's existing urban forest canopy in terms of stormwater costs and modeled the effects of trees in slowing stormwater given various urban development options.

Finding suggest that if Garland's existing tree canopy cover was removed, the city would have to contend with 19 million additional cubic feet of stormwater. The cost to build retention facilities to handle this additional stormwater would be $38 million (This would be about $2.8 million annually, based on a conservative. $2 per cubic foot cost of constructing retention ponds. These construction costs are based on the assumption that such facilities are rebuilt or that significant maintenance work is performed every 30 years. Annual benefits are essentially treated as avoided annual payments on a 6 percent interest loan over 30 years, which would otherwise be necessary to construct the additional facilities.)

The analysis is based on the Natural Resource Conservation Service's methodology for assessing stormwater flow in small urban water sheds. Known as Technical Release 55, the model is the most widely used for the application in the United States.

The city of Garland has now put all the pieces of the puzzle together toward meeting EPA's clean water program. The city can offer property owners a direct incentive for reducing the amount of stormwater that flows off their property.

By reducing the amount of impervious surface and increasing the number of trees and other vegetation. Citizens can reduce their stormwater utility fee. City managers can now show citizens the dollars saved in doing so, using AMERICAN FORESTS' CITYgreen. With these incentives, the city of Garland will be greener and its waterways cleaner.

Communities across the country must contend with the same stormwater and water quality issues and regulations as Garland, Texas. The city's innovative approach to managing stormwater can be considered a model for others. A comprehensive approach to stormwater management includes nonstructural BMPs--increasing urban tree cover to slow stormwater runoff and improve water quality. Cities can now link a reduction in impervious surfaces to a reduction in stormwater fees. With CITYgreen they can show people the direct relationship between increased tree canopy and reduced stormwater runoff. As the nation works toward improving water quality, every city can employ these strategies so that the goals set by the Clean Water Act a quarter-century ago can become a reality in our lifetime.

Jeff Beattie, Cheryl Kollin, and Gary Moll are part of AMERICAN FORESTS' Urban Forest Center, Beattie as natural resources analyst, Kollin as director, and Moll as vice president.