Authors

Noah Tobinsky, Sabrina Fang, Ayesha Islam

Research Question

How can NYC leverage a stormwater charge and credit program to promote on-site stormwater management on private property?

Background

Rainfall events are becoming more frequent and severe due to climate change. NYC's drainage network consisting of combined sewer and separate stormwater sewers have performed sufficiently for most of New York's history but were designed based on historical precipitation data from the beginning of the 20th century. For NYC to manage the storms of today and tomorrow, NYC DEP needs to continue to invest in both green and gray stormwater infrastructure.

Over 70% of NYC is covered in impervious surfaces. Stormwater from these areas can cause street flooding and overwhelm the sewer system. DEP is leading stormwater management efforts on city-owned property, and through private property incentive programs and policy regulations. However over 50% of land in areas targeted for GI is privately owned. DEP is interested in implementing a stormwater charge to incentivize GI on private property. This project aims to analyze existing stormwater charge policies in the U.S., analyze sites for SW management in mixed development areas, and recommend guidelines for a potential stormwater credit program in NYC.

DEP is currently investigating the benefits and feasibility of a stormwater charge to fund its stormwater management efforts. Under this hypothetical charge, customers will be charged for their usage of the stormwater system using the amount of impervious area on their property. Additionally, if this charge were to be enacted, DEP would offer discounts to customers if they manage stormwater on their property through impervious area removal or implementation of stormwater management practices (SMPs) like rain gardens, green roofs, cisterns, etc.

Methodology

This project will include a review of existing stormwater charge/credit programs from other utilities, including strategies leveraging community partnerships to administer the credit program and/or stormwater grants. Additionally, a SMP siting analysis will be performed on non-residential properties in mixed development areas using our impervious data layer. This analysis includes hydrological modeling, ROI calculations considering a hypothetical stormwater charge, and recommendations for siting infrastructure. Deliverables for this project would include a literature review of stormwater credit policies and technical write up on the SMP site analysis.

Deliverables

• Literature review of selected peer cities: stormwater charge/credit policy, strategies to increase credit participation, leveraging community groups/non-profits, program impacts and best practices
• Site Analysis within mixed development areas: SMP recommendations/typologies for credit program, return of Investment of SMPs under stormwater charge and credit scenario, recommendations for siting SMPs based on building/location characteristics.
• Credit Explorer / Website and Stormwater charge calculator including the ability to pick out parcels, and model how different SWM would impact runoff.
• Potential for machine learning component, through training a model to suggest SWM projects / Suggest parcels that are feasible/ideal for SMPs.

Data Sources

• NYC Department of Environmental Protection (DEP): Stormwater Charge and Crediting Information and Impervious Surface Layer on NYC Open Data