NYCDEP Green Infrastructure

The purpose of this paper would be to study both the cost and hydraulic effectiveness of the rain gardens in New York City. In 2012, New York City started to use rain gardens throughout the city as a cost effective method to reduce the water flowing into the sewer system. The rain gardens initially have a higher upfront cost, with some contracts averaging $40,000 per rain garden, compared to the standard practice of piping or detention tanks but the maintenance cost will save in the long term. The current New York City sewer system also overflows during huge rain events so decreasing the amount of water or detaining some of it will help reduce the overflow and allow the system to last longer. Since 2012, there have been over thousands of rain gardens planted and still thousands more that will be constructed this upcoming spring. New York City Department of Environmental Protection has estimated that the first 90 rain gardens planted in Gowanus would be able to absorb over 8 million gallons of water each year. Over the last few years, there have been several design changes to help make them easier to construct and to allow for more stormwater collection. These changes, such as new types of rain gardens, allows the city to place rain gardens in more areas, reducing the amount of impervious area and replacing it with pervious area. The types of rain gardens that New York City currently uses are standard, green-strips, infiltration basins, and stormwater green street (SGS) all differ by their dimensions, siting criteria, amount of filtration, and detention rates. The green-strips are used for areas where there is limited room due to their reduced width. Infiltration basins are used for areas with lots of entrances because they can be designed with concrete tops for people to walk on. SGS are used in the streets where there is adequate space for them (very rare). The rain gardens not only help with increasing pervious area but they also help with water quality, helping remove nitrogen from the water before releasing it in to the sewer system. There have been several studies of areas with high chances of flooding due to the poor state of the sewer infrastructure with how much flooding they have. Recently, there have been rain gardens installed in these areas (such as Jamaica, Queens) and the amount of flooding will be measured to see how much the rain gardens have helped with the reduction of flooding. Knowing the amount of rainfall for each of the storms will also help in estimating the amount of inflow into the rain gardens. NYCDEP has several excel sheets available to calculate nitrogen removal and stormwater detention which can be compared to the experimental data from the field.