City of Plattsburgh Stormwater Conveyance System & Green Infrastructure Planning. Technical Report #79.

Farrington, K. (2015). City of Plattsburgh Stormwater Conveyance System & Green Infrastructure Planning (Technical Report No. 79). Grand Isle, VT: Lake Champlain Basin Program.

The City of Plattsburgh (City) is the most urbanized area within the New York State Lake Champlain Basin. Land-use varies from residential areas with small and large parks and schools to the industrial sections and the highly commercialized downtown. All of these areas contribute to the imperviousness of the land within the City, which creates a large amount of stormwater runoff that is conveyed through the City’s sub-surface separate stormwater sewer system to 41 outfalls that discharge directly to Lake Champlain, the Saranac River and their tributaries within the City.

In an effort to fully understand the conveyance of stormwater within the City and identify vulnerabilities within the stormwater system, the City undertook an extensive mapping project that included identification and data collection for all stormwater trunklines. Information was digitized from existing paper maps, as well as collected by City staff throughout the summer of 2013, and includes data on storm sewer manholes, catch basins, storm sewer mains and combined sewer mains. This information was then utilized within the US EPA SWMM computer model to complete sub-sewershed mapping, which ultimately identified 54 principle sub-sewersheds within the City’s system, and identify areas within the City that are or will be prone to flooding during 5-year, 10-year, 25-year, 50-year and 100-year design storm scenarios. Outcomes of the modeling include the identification of the manholes that surcharge above rim elevation and identification of the areas with an increase in flood volume
throughout the City as the higher intense storms transpire.

Information obtained from the modeling was then used to identify 12 City or school district owned sites directly within or adjacent to flood prone areas that can be used as sites for green infrastructure retrofit project implementation. The sites were ranked based on a matrix created by the project partners that takes into consideration project achievability, stormwater volume reduction potential and stormwater quality impacts. Of the 12 projects, the US Oval parking lot was ranked as the highest for implementation, and use of green infrastructure practice ranking matrix indicated that a bioretention area would reduce water quantity while improving water quality at the site.

In the spring of 2015 the City constructed a bioswale and bioretention basin at the US Oval that was designed to collect stormwater from 2.5 acres, of which 1.5 acres is impervious surface. The bioswale was constructed to convey at least 4.6 cfs, and is connected to the bioretention basin via an underground pipe. A basin area of 1200 square feet with total volume of 9700 cubic feet was constructed to receive 8300 cubic feet of water quality volume. The basin also contains several New York native plant species, and two educational signs have been installed at the site.

On July 27, 2015, a ribbon cutting was held at the basin to mark the opening of the first green infrastructure project within the City of Plattsburgh. Members of the press, as well as residents, attended the event to learn about the project and become educated on the City’s plans to continue addressing stormwater runoff in the future.