Philadelphia’s green infrastructure plan will turn one-third of the city’s impervious asphalt surface, or 4,000 acres, into absorptive green spaces. The goal is to move from grey to green infrastructure. Grey infrastructure includes “man-made single purpose systems.” Green infrastructure is defined as “man-made structures that mimic natural systems.” As an example, green roofs, bioswales, networks of man-made wetlands, restored flood plains, or infiltration basins would all qualify as green infrastructure. The benefits of such systems include: evaporation, transpiration, enhanced water quality, reduced erosion / sedimentation, and restoration. Some grey / green infrastructure feature integrated systems that create hybrid detention ponds or holding tanks, which are designed to slow water’s release into stormwater management systems.
Set clear, ambitious targets and deadlines for reducing stormwater runoff in the District and measure progress against targets. Like New York City and Philadelphia, develop a robust green infrastructure action plan that leverages existing grey infrastructure systems. Enact green infrastructure rules that enable the use of fines for private properties that don’t store their own runoff.
According to the U.S. Environmental Protection Agency, the average family of four uses 400 gallons of water every day, and some 70 percent of that water is used indoors. Of indoor use, some 16 percent is consumed by showers, 16 percent by faucets, and 22 percent by clothes washers. These numbers are highlighted because these are all forms of greywater that can be reused.
Washington, D.C., should develop more stringent guidelines and rules that encourage commercial owners and homeowners to use appropriate (native and adapted) plants and develop systems that infiltrate, store, and recycle water, limiting the use of valuable potable water for landscapes. Residential systems such as bioswales / bioretention ponds, rainwater gardens, and water recycling and drip irrigation can all be used to efficiently conserve water. Commercial owners and homeowners should be allowed to use “Living Machines,” or constructed wetlands, which are systems that recycle and reuse greywater (and even blackwater), for landscape maintenance and other safe re-uses like toilet-flushing and car-washing.
Separately, Washington D.C. should also ensure all parks and public green spaces meet the highest standards of water efficiency. This can be achieved in part by requiring parks and public green spaces to use appropriate (native and adapted) plants. The Sustainable Sites Initiative (SITES) presents a model for achieving these goals. New York City and other cities have also created local guidelines. Washington, D.C. should also use its own parks to undertake a broad public education campaign about water efficiency in the city.
Washington D.C. should incentivize water efficiency measures by requiring the use of appropriate plants in public and residential landscapes, and enabling filtered or treated greywater (and even blackwater) reuse for landscape irrigation.
As city managers know, green roofs are necessary for taking pressure off of over-worked combined water / sewage systems. The EPA cites some powerful data: Green roofs can catch 40-60 percent of stormwater, reducing flow into a city’s sewers. Ken Sandler, with the Office of Federal High Performance Green Buildings at the General Services Administration, adds that recent U.S. government research shows that green roofs retain 1.5 inches of stormwater runoff. Also, Steven Peck, Honorary ASLA, head of Green Roofs for Healthy Cities, says all that retained stormwater has great financial benefits: The average stormwater mitigation benefit is $4.26 per square foot. Like Philadelphia, Washington, D.C., should get the word out on the benefits and create a public education program on how to use green roofs for residential stormwater management.
In addition, Washington, D.C., has the opportunity to be an innovator by enabling the use of rooftop rainwater cisterns to water green roofs during the hotter months, saving on any potable water use for watering purposes.
D.C. should follow Toronto’s lead and mandate the use of green roofs in all new buildings. To address older structures, the District can follow Philadelphia’s lead an introduce a stormwater runoff fine, which will incentivize the use of green roofs, bioswales and permeable pavements — systems that not only cool but also store stormwater. The city can also incentivize the use of green roofs in older buildings by providing tax breaks for feasibility studies and other preliminary design assessment costs.
As city park managers already know, a park may look green but not actually be green. Many cities are investing in ensuring park lawns are actually pervious and store water in plant roots and soils. According to one study, regular lawn is about 80 percent as impervious as asphalt, so not all green spaces are pervious. To ensure D.C.’s green spaces maximize their ability to mitigate stormwater runoff, Sustainable Sites Initiative (SITES) guidelines on soils, vegetation, and hydrology should be applied.
Improve the permeability of the District’s parks and improve their ability to capture and store water.
Some cities like Toronto have invested in innovative multi-use infrastructure. As an example, Sherbourne Commons is not only a remarkable public space but also a water treatment facility. In a marvel of thoughtful design and engineering, the new 3.6-acre, $30 million park commissioned by Waterfront Toronto and designed by a team led by landscape architecture firm Phillips Farevaag Smallenberg uses ultraviolet light to clean polluted water coming in from Lake Ontario.
Create multi-use infrastructure — parks with rain gardens and bio-retention systems along with water treatment systems — turning them into smart green infrastructure.
At an event at the National Building Museum, Jennifer Toole, ASLA, the designer of Washington, D.C.’s bicycle infrastructure, said that the city should come up with a plan for integrating bicycle and green stormwater management infrastructure together into one system. Other cities like Portland have used curbs as locations for bioswales.
Washington, D.C. ,has experimented with green street pilot projects in the past. Using lessons learned from those pilots, the city should create permanent green street corridors in multiple neighborhoods, just as Vancouver and San Francisco have done to great success. In the case of San Francisco, the city agencies addressed the coordination challenges between the agencies by basically throwing out the code for the first corridor and then building a new framework from the experience. One such location for a green street corridor would be on Eye Street (in front of the ASLA headquarters) from 6th through the new CityCenter development. ASLA would provide the public education component for this green street.
The city could experiment with carefully redesigning components of the city’s many historic circles so they become circular stormwater management systems. Also, like Chicago, Washington, D.C. should start a green alley program using the latest permeable pavement and asphalt technologies.
Increase the use of bioswales near transportation systems (like bike lanes), add in permanent green street corridors in areas where the traditional combined water / sewage system is under heavy strain, and develop a green alley program.
As city officials already know, trees provide excellent stormwater management benefits as they capture rainfall with their leaves and through their roots and leaf litter create soil conditions that enable water absorption.
However, at last year’s GreenBuild, Peter MacDonagh, the Kestrel Design Group, made the case that larger, older trees are far more valuable than younger ones in terms of stormwater management, so work needs to be done to preserve these and use new techniques to enable younger trees to stay in place longer. Citing data, he argued that a tree with a 30-inch diameter provides 70 times the ecological benefits of a 3-inch diameter tree. For example, a large tree intercepts 79 percent of rain hitting the ground, providing the “best green infrastructure you can find.”
Washington, D.C., should further invest in ensuring the current 6 percent tree mortality rate is further lowered and larger, older trees are kept healthy. One way to do this would be to use larger tree boxes with structured soils and add permeable pavements around the trees, which would enable the tree to both grow and get enough water, capturing stormwater in the process.
Continue to expand urban tree canopy and preserve larger trees to manage stormwater runoff. Spread use of tree boxes and permeable pavements for stormwater capture.
Separately, Washington, D.C., should also ensure all parks and public green spaces meet the highest standards of water efficiency. This can be achieved in part by requiring parks and public green spaces to use appropriate (native and adapted) plants. The Sustainable Sites Initiative (SITES) presents a model for achieving these goals. New York City and other cities have also created local guidelines. Washington, D.C., should also use its own parks to undertake a broad public education campaign about water efficiency in the city.
As part of a public education campaign, parks and public green space should follow the highest water efficiency standards.