New York City’s Green Infrastructure Plan is a bold initiative to leverage multiple benefits of using vegetated green stormwater management. Their plan lays out three big goals: 1) Reduce the city’s combined sewer overflow (CSO) volume by an additional 3.8 billion gallons a year (about 2 billion gallons a year more than the all-Grey Strategy); 2) Capture rainfall from 10% of impervious surfaces in CSO areas through green infrastructure and other source controls; and 3) Provide substantial, quantifiable sustainability benefits, such as cooling the city, reducing energy use, increasing property values and cleaning the air that the current all-Grey Strategy doesn’t provide. Grey infrastructure is vital to the city moving forward, but it will take a less important role and be combined with green infrastructure using “distributed assets.”
Derick Tonning, New York City Department of Environmental Protection Office of Green Infrastructure, shared insights into the city’s journey during the LID Conference in Portland, Maine, last fall. Most, about 90% of New York City’s green infrastructure stormwater management program, will be carried out in the right of way (ROW), he explained.
At the time of Derick’s presentation, about 150 to 200 ROW practices were under contract. “All [stormwater] practices have plants, most have trees.” Installation is ideally timed during the planting season.
The New York City team has learned critical lessons in writing the contracts for rain garden installation. For instance, to be sure to include language covering traffic management, litter removal and safety barriers during construction. Quantifying expectations is also critical: How much is the contractor responsible for? In New York City, the contractor must guarantee the hardscape for one year; plants for two years.
Litter is a main issue, Derick said. It’s not good for the city when citizens see rain gardens continually filled up with trash. One very important observation is that the longer a practice stays with the contractor, the less attention is paid to maintenance. The city’s goal is to flip them over to their own maintenance teams quickly.
Communicating with city residents is important to success of the program. “With so many distributed assets, it’s hard to have signs at each location,” he said. Neighborhood communication includes door hangers in neighborhoods where construction will be taking place and a city hotline to field questions. DEP also assigns staff construction liaisons.
Coordinating with other city stakeholders is also critical, especially the Departments of Transportation, Buildings and Sanitation. For instance, DOT street milling and resurfacing can destroy BMP functionality. The solution has been communication and design modifications to make it easier for DOT to go around aprons.
Another solution has been to enter the location of bioswales in the Department of Buildings database so that construction scaffolding doesn’t get placed in the rain garden. Derick’s team has learned that the city’s departments track assets differently: DOT tracks between intersections, while the Department of Buildings does it by lot, and DEP works by GPS.
Construction sequencing is very important, he said. In the beginning, the city didn’t include instruction on construction sequencing in contracts. Contractors would put the hardscape in first and then excavate. Contractors must also precisely measure to meet design specs so that facilities meet DOT requirements. Specific contractors may be accustomed to specializing in an aspect of what’s needed to correctly construct a NYC raingarden — for instance asphalt, trenching or landscaping. However, these green infrastructure distributed assets require knowledge of all of it.
Tree guards go around all plants, Derick said. A stone strip at the edge accommodates people getting into or out of cars on the street. Epoxy has been added to the specs to hold them in place. They’ve also improved the design in of inlets to accommodate random foot traffic.
DEP has also become aware of watching how many sites an individual contractor keeps open at once. In the beginning, a contractor would partially complete five sites and move on. Those sites became litter baskets and deteriorated. “They need to pay attention to it at all times.” (In the next issue, look for insights into NYC rain garden maintenance).
• New York City Green Infrastructure Plan
• Standard Designs and Guidelines for Green Infrastructure Practices
• Report for Post-Construction Monitoring Green Infrastructure Neighborhood Demonstration Areas
February 1, 2017 NewTerrain