3. Minimize street flooding and end sewer back-ups by tackling their root causes
Guaranteeing Infrastructure Investments > Recommendations
The causes of street flooding and sewer back-ups are not as obvious as they might first appear. There are neighborhoods far from the area of interest, such as parts of Downtown Brooklyn, Prospect Heights, Carroll Gardens, and Boerum Hill, where the storm and waste water management of these areas deeply impact the Gowanus neighborhood. Meanwhile there are closer areas, such as Park Slope, where the sewage management capacity does not affect Gowanus’ sewer back-ups (see Fig. 1). To address the Gowanus neighborhood’s flooding and sewer back-up problems, interventions must be strategic and encompass both upland and neighborhood actions.
Ground action in science and engineering
Through the community planning process, strong concern has been expressed about the need to better understand how site-by-site interventions to mitigate flooding from rain and storm surges impact the area’s hydrology. Any intervention should not create adverse hydrological impacts within the area, either by exacerbating flooding for surrounding property owners or impeding drainage further inland and uphill. As noted above, as a result of input gained through the Bridging Gowanus process, the de Blasio Administration agreed to broaden the flood gate feasibility study to include storm water management, run-off, water-flow, and coastal protection issues. It will now investigate how storm surge barriers would impact nearby properties and infrastructure, as well as drainage. Attention should also be paid to synergy with Red Hook, where the State and the City will develop a comprehensive flood management system, and where the community has proposed conducting a drainage study to analyze existing conditions related to frequent flooding. Clear, accurate, and comprehensive information about the hydrology should help guide decision making about flood management in Gowanus. This study must be completed, and whether or not floodgates make sense, a plan must be developed to address both coastal protection and storm water flooding.
Upland: Improve storm water management
Upland interventions are measures aimed at decreasing the amount of waste water and storm water generated in neighborhoods that drain into Gowanus via the combined sewer system, from Downtown Brooklyn, Prospect Heights, Carroll Gardens, and Boerum Hill. Meaningful interventions in those neighborhoods will reduce system overloads and improve conditions around the entire canal. This should be through design practices for new development, retrofits of existing sites, and the installation of green infrastructure. DEP’s efforts through its GI Bioswale Construction Project, which will bring dozens of bioswales to the Gowanus watershed in 2015, are a great step in the right direction.
Gowanus Neighborhood: Restore the waterfront ecosystem
New, water-absorbent park space along the canal and wetland restoration projects should strongly support storm water management goals. There are many projects and proposals for these types of multi-functional spaces in the area, such as Sponge Park and the 6th Street Green Corridor. All such efforts could be connected to the Superfund remedy and/or brownfield remediation efforts. Their benefits should be quantified and integrated into the plans for achieving storm water management goals for the area.
Identify sites for storm water controls, leading by example on public sites
City-owned land in the areas that drain to CSO outfalls along the Gowanus Canal including parks and schools should be considered as potential sites for additional green infrastructure projects (such as green roofs and water plazas) to minimize storm water run-off. There should also be attention given to matching new green infrastructure projects to the historical structural patterns of where water flows and drains. The Environmental Quality Partnership (see recommendation 10 in this section) can serve as a venue for identifying a variety of funding sources. A plan to phase in storm water capture improvements on public sites can synch up with the Long Term Control Plan goals and timeline. It is estimated that improvements to the public sites alone in areas that feed in to the Gowanus Pump Station could reduce storm water runoff by 5%.
Shape new development in the Gowanus sewer-sheds
New development sites should aspire to produce zero storm water run-off. Developments should be incentivized to exceed DEP’s existing Performance Standards, especially through green infrastructure, grey water reclamation, and rainwater harvesting. For substantially sized development sites close to major sewer lines, the installation of retention tanks to absorb excess storm/waste water would provide a major benefit to the system and should be explored.
Gowanus is not the only New York City neighborhood that bears the burden of accepting runoff from surrounding neighborhoods. To solve the downstream problem, there must be an effective coordination mechanism that guides storm water planning across neighborhoods, Community Boards and other jurisdictions. The Environmental Quality Partnership (recommendation 10 in this section) provides an opportunity to design effective management models; the knowledge that emerges from such an effort should be further developed to inform a DEP pilot program. If effective, this could be a model that is extended to other sewersheds facing the same issues.