Water quality director speaks on green infrastructure, stormwater management in Gentilly
Brady Skaggs, Ph.D., introduced and discussed green infrastructure and its applicability at a lecture at the Lake Pontchartrain Basin Foundation office on Wednesday, July 12.
According to Skaggs, the Water Quality Program Director for the foundation, green infrastructure is a way to manage rainwater through non-energy-intensive means and vegetation. Green infrastructure is found in best management practices and stormwater ordinances, he says.
Managing rainwater is important in New Orleans, a city that receives 64 inches of rain every year—third most in the United States according to WeatherBill.com.
After massive rains in August 2016 overflowed 10 rivers, 20 parishes experienced flooding. It is likely to happen again, Skaggs said, so cities should be prepared to handle excessive rainfall.
“The probability for an event like this to happen again anywhere in this region is one in 30 years,” he said.
Green infrastructure can have a substantial impact on flooding, because flooding occurs when the grey infrastructure–pipes and pumps–are unable to handle the water coming in. Green infrastructure, in its various forms, is intended to impede the amount of water that reaches the pipes.
According to the City of New Orleans’ Comprehensive Zoning Ordinance Article 23, Storm Water Management Plans have to have Best Management Practices that include “primarily green stormwater infrastructure features for the purpose of extending the time of concentration to the drainage system, filtering runoff through plants and soil, and reducing total runoff.”
In order to appreciate what green infrastructure can mean, Skaggs made it clear what effect a property’s size has on water runoff.
“A 1500-square foot house in a 1-inch rain event can contribute 925 gallons. A 1000-square foot driveway can have as much as 617 gallons of runoff,” Skaggs said. “2500 square feet of other impervious surfaces can contribute to 1500 gallons of rainwater runoff.”
The City of New Orleans’ Comprehensive Zoning Ordinance Article 23 lays out 21 different forms of green infrastructure that have to be included in developments or redevelopments of 5,000 square feet, or one acre. These include detention/retention basins, rain gardens and bioswales. Some of these can already be found in the city. In the neutral ground on Fillmore Avenue is a bioswale. Skaggs explains how it works:
“[The Fillmore avenue neutral ground] looks like a park but is specifically designed to retain stormwater. Water will build up around that middle island and flow into this box and into the storm drain. If you have a rain event that is less than 1.2 inches, most of that rainwater is going to be captured and retained on site. The overflow will go into the storm drain system.”
Skaggs and his colleagues are trying different various best management practices at different bodies of water around the Greater New Orleans area. The first is the St. Tammany stormwater pond-sampling project.
They are using three lakes in three different neighborhoods in St. Tammany, Del Sol, Casa Bella and La Barre. In each pond, they tried a different practice. The data on these studies is not available yet.
“At Del Sol we worked with another organization that constructed a floating wetlands system. There’s PVC pipe that’s floating on the surface and plants are structured around that,” Skaggs said. “It’s floating so it moves with the height of the lake.”
“The initial design of the study was to look at the comparison between the means and the variability of what is going into the lake and coming out of the lake,” Skaggs added.
Skaggs and his colleagues at the foundation are also working on a project in the Pontilly Neighborhood Stormwater Network in New Orleans’ Gentilly neighborhood. The network is part of the Gentilly Resilience District, and the project in Gentilly has just begun.
“Pre-construction sampling activities have commenced. They’re going through the process of building those BMPs (best management practices) now. Once construction is complete, we’ll be back out there sampling those areas and looking at the data,” Skaggs said.