Pontilly Stormwater Management

by Dana Brown, FASLA, PLA, AICP, LEED AP

Streetscape design for stormwater runoff
Street basins receive runoff from along the curbs and gutters and detains the water. These curb extensions have the added benefit of reducing the distance pedestrians must cross street, resulting in traffic calming and improved pedestrian safety. / image: Dana Brown & Associates

The 900-acre Pontilly area of New Orleans is composed of two moderate-income, minority-majority neighborhoods—Pontchartrain Park and Gentilly Woods. For decades, these neighborhoods have repeatedly experienced losses due to flooding and both were severely damaged by Hurricane Katrina with hundreds of homes destroyed.

In response, the neighborhoods collaborated to form the Pontilly Disaster Collaborative (PDC) that seeks solutions to localized flooding issues caused by rainfall events. PDC approached the New Orleans Redevelopment Authority (NORA), who had received ownership of many residential properties in Pontilly following Katrina, to utilize vacant lots for managing stormwater. A landscape architect at NORA recognized the value of the community organization’s idea and began seeking funding through the FEMA Hazard Mitigation Grant Program (HMGP).

The Pontilly Hazard Mitigation Project is funded through FEMA’s Hazard Mitigation Grant Program. It took enormous efforts by the NORA landscape architect and a FEMA representative to convince FEMA funders that green infrastructure should be constructed, not the administration’s standard catch basins, pipes, and canals. These women’s insistence on a higher standard The insistence by these women to set a higher standard resulted in the first FEMA project to employ green infrastructure as mitigation. NORA was awarded $15M for design and construction of this project.

Depths of flood levels in modeled 10-25-100 year storm events  / image: CDM Smith

Winners of the project include the engineering company CDM Smith serving as lead consultant with landscape architects Dana Brown & Associates (DBA) as sub-consultant. The project team analyzed the land cover, topography, and drainage system; modeled hydrologic and hydraulic processes; and designed stormwater management system alternatives to manage rainwater as close as possible to where it falls. This approach called for a distributed but connected series of green infrastructure facilities that detain, filter, and infiltrate stormwater runoff. The alternatives were evaluated for efficacy of flood risk reduction as well as providing many other benefits. HMGP funding requires proof through modeling that the economic value of benefits would equal or exceed the level of grant funding, which was provided through benefit-cost analysis (BCA).

Graph shows 10-year storm events (short, intermediate, and long events) over 24 hours in comparison to the rate at which the massive pump systems can pump the water out of the below sea-level city. A May 8, 1995 rainstorm produced 12.25 inches of rain in seven hours. During peak hour, 3.75 inches of rain fell. / image: CDM Smith
The mid-level concept for green infrastructure interventions was selected during preliminary design for modeling and further evaluation. / image: Dana Brown & Associates
The mid-level concept for green infrastructure interventions substantially reduces flood levels as indicated by the hydrologic and hydraulic modeling performed by CDM Smith. / image: CDM Smith

The HMGP grant is currently funding $13.5 M in construction of stormwater management interventions as retrofits in these older neighborhoods. Issues addressed include heavy clay soils, severe soil subsidence, and drainage pipes and pumps taxed beyond their capacity. Working with CDM Smith water resource engineers, DBA designed stormwater detention areas on residential lots on which owners did not want to rebuild, creating small open space areas known as stormwater parks. Bioretention cells at intersections in curb extensions, also known as street basins, and urban bioswales between curbs and sidewalks are being constructed. Parallel parking lanes on key streets are also being reconstructed with pervious pavers.

Stormwater lots receive runoff from the street and from drainage pipes in the street, detaining the water until the drainage pipes can accept more rainfall. During this time, the pollutants are removed from the runoff, plants take up the water, and the groundwater is recharged. / image: Dana Brown & Associates
Pervious paving in the parallel parking aisles serve as inlets and provide subsurface storage for groundwater infiltration. / image: Dana Brown & Associates

Models show significant reductions in flood water levels and in the number of properties potentially damaged. The BCA captured the value of air quality improvement, water quality improvement, and forthcoming tangible benefits such as strengthening of the social community, reduced air temperatures, and improved neighborhood walkability.

Dana Brown is a native of New Orleans, and has worked tirelessly to address the U.S. Environmental Protection Agency and Louisiana Department of Environment Quality requirements for water quality. She has written and revised chapters of the development code for several municipalities and parishes. She authored a manual to guide developers and design professionals in designing and implementing stormwater best management practices and organizes and leads dozens of stormwater workshops each year.

Advertisements

2 thoughts on “Pontilly Stormwater Management

  1. Clara E Aleman March 31, 2019 / 10:24 am

    Ms Brown, thank you for contributing this article. I have found that working on water quality issues, is not just a career, it is a mission. The information is clear, concise and has beautiful visuals. My question is about the graphics, can you please share what software you use to produce the graphics? And again, I thank you for all your efforts.

    • sihui April 11, 2019 / 2:39 am

      i want to know too

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.