Christopher Cox realized before dawn on Sunday that his family might not be able to stay in their Baton Rouge home much longer.

They lived 10 minutes away from the Amite River, which was swelling with the continuous rainfall. Cox, 21, had been checking the water level periodically all weekend, and when he saw it had crept up to the front door, his family decided it was time to leave. Volunteers from a neighboring parish were bringing in boats to help evacuate people, and he helped his parents and grandmother—who had left her own flooded house the day before—wade through the murky water to the canoe.

“Most of what we were going through was sewage,” he recalled. “There was debris and trash everywhere. It’s terrible for you. We were told that after coming into contact with the water, we would have to find a place to bathe as soon as possible.”

Louisiana witnessed unprecedented flooding over the weekend that caused 11 deaths and necessitated more than 30,000 rescues. According to the National Weather Service, more than 20 inches of rainfall deluged some parts of Baton Rouge within 72 hours. And across the region, newspaper accounts told of sewage overflow of the type Cox experienced.

Experts say Baton Rouge’s sewage system—an intricate network of piping, lift stations and booster pumps built nearly a century ago—was unable to handle the weekend’s torrential downpour, leading to what is known as a “sanitary sewer overflow.” It’s a threat facing many U.S. cities with older sewage networks that are eroded by growing urban populations, tree roots, debris and illegal connections. Unexpected heavy rainfalls introduce too much water into the system and can cause pump stations and treatment plants to break down, as well as untreated sewage to overflow from manhole covers and pour into water bodies.

Climate change, and the heavier rainfall it is expected to bring, could make things worse. According to the National Climate Assessment, U.S. average precipitation per year has increased by 2 inches between 1895 and 2011 and is projected to continue rising across the northern part of the country. Experts say this could create a sewage burden that cities need to plan for.

“With increased precipitation, even more runoff is going to be making its way into these systems and reaching a volume that could create an overflow. If we don’t do something to engineer our way out of this, we’re going to see it become a bigger problem,” said Anne Jefferson, assistant professor at Kent State University’s Department of Geology.

Take Ellicott City. A few weeks ago, flooding in that Maryland town broke a pipe that released millions of gallons of untreated sewage and stormwater into the Patapsco River. The problem is compounded in areas like New York and Washington, D.C., which have common pipes for sewage and stormwater, called combined sewer systems. The District of Columbia Water and Sewer Authority estimates that anything more than an inch of rainfall in D.C. could lead to a “combined sewer overflow” that contaminates the water bodies around it for up to three days.

Increased rainfall could lead to overflows in cities that have combined sewer systems, as well as those that do not, but according to Jefferson, the former will face the brunt of the problem.

“Cities that don’t have combined systems still end up with stormwater in their sewers through infiltration and inflow, which can cause overflows and backups. But it’s much more of an issue in cities which do have them,” she said.

Green solutions

Combined sewer systems are a product of centuries-old planning and development. Prior to their development, urban populations disposed of sewage by dumping it in streams and rivers. Later, they began to bury these streams and connect them with drains, which collected rainwater and sewage and were released into larger water bodies.

“As technology arose to treat wastewater in the late 1800s, there was already a legacy of pipes and streams, and it was a natural evolution to take these pipes and have them lead to newly built wastewater treatment plants,” explained Jefferson. According to her, 772 communities in the United States have combined sewer systems. It’s difficult to estimate the quantum of overflows they lead to, but a 2004 U.S. EPA report pegged it at about 850 billion gallons being discharged into American waterways.

Municipalities across the country are employing different approaches to grapple with the issue. Broadly, they fall under two categories: investing in pre-existing “gray” infrastructure—like expanding pipes, building storage tunnels and treatment plant capacities—and opting for green infrastructure, which essentially tries to keep rainwater out of sewage systems using pervious street surfaces, rain gardens and bio-retention.

These approaches are defined in consent decrees signed between municipal authorities and EPA under the Clean Water Act. Cleveland’s consent decree, which was signed in 2010, was the first to allocate a budget for green infrastructure, Jefferson said, adding that other cities have followed suit and are opting for a combination of gray plus green solutions.

Cities like Kansas City, Mo.; Cincinnati; Philadelphia; and Pittsburgh are all veering toward greener solutions, which might be more sustainable in the long run, according to experts including Tim Duggan, a landscape architect who helped design Kansas City’s green infrastructure sewage model. Pipes, storage tunnels and treatment plants are designed with fixed volumes in mind, meaning increased precipitation patterns could pose a problem over time. “If you build a concrete box, you’re going to have to make another one eventually. But green infrastructure has flexibility and resilience. We don’t have a crystal ball to forecast climate change, but if we design a flexible, adaptable system, it will be resilient,” said Duggan.

In D.C., which has a partly combined system, sewage outfall points exist on the Potomac and Anacostia rivers, as well as Rock Creek. About two-thirds of the outfall quantity is released into the Anacostia, and because it has a shallow slope that doesn’t allow for toxins to easily flush out, it’s the most affected water body in the district.

“In 2005, the city signed a consent decree with the EPA that was gray-infrastructure-based. At the beginning of this year, we formally modified it to allow for both gray and green infrastructure,” said Bethany Bezak, green infrastructure manager with the D.C. Water Clean Rivers Project. She said a potential 20 percent increase in rainfall has been factored into their engineering designs.

“We feel that’ll help us deal with any effects of increased rainfall or climate change,” Bezak added.

New York City, on the other hand, has an entirely combined system and currently releases billions of gallons of sewage into the harbor.

“There are 450 outfall pipes that release untreated sewage and stormwater when there are rain events of a significant size. This doesn’t necessarily mean monster floods—even a quarter-inch can make a difference,” said Willis Elkins, program manager of the Newtown Creek Alliance.

The city doesn’t track outfalls, but according to Elkins, estimates indicate that 3 billion gallons are released into one stream, Newtown Creek, annually. The municipal authority is constructing additional capacity in treatment plants and storage facilities but is also trying to find ways to use natural solutions like water catchment systems.

“These are more cost-effective and have the added benefits of providing habitats for animals and improving air quality,” said Wilkins.

King County in Seattle is also focusing on a combination of gray and green solutions to reduce its current annual outflow of 1.5 billion gallons. John Phillips, water quality planner at the county, said it has designed a system to carry 2.25 times the average wet weather flow. “In addition to this, we’re focusing on bio-retention, which means we can infiltrate the flow into the ground—either at the surface or at a deep depth under the soil,” he said. “If we can infiltrate the water deeper, there are a lot of positives, because it can merge with the groundwater and improve groundwater conditions.”

King County has also created an interactive map to keep residents aware of where overflows are taking place and how to avoid them.

Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. E&E provides daily coverage of essential energy and environmental news at Click here for the original story.