Posted on September 22, 2021
Say “storm drains” to people and their eyes might glaze over.
Talk to them about the flooding that inundated the state after the remnants of Tropical Storm Ida dumped record rainfall on the state and that’s something most can relate to.
Flash flooding from Ida washed away cars, inundanted basements and streets and was blamed for the deaths of 30 people in New Jersey. Can future storm flooding be stopped or at least made less severe?
The essential underground network of pipes and drains that Ida overwhelmed will have to go through massive changes to handle the storms of the future, which will only get worse due to climate change, said experts interviewed.
What needs to be built in Ida’s wake is different than the resiliency projects after Hurricane Sandy that elevated homes and other structures above the level of flood waters.
“This (Ida) was a different event. Sandy was a coastal event, Ida was an extreme rain event,” said Franco Montalto, Drexel University professor of environmental engineering. “This was like (Hurricane) Irene on steroids.”
Ida’s record-breaking rainstorms overwhelmed the ability of stormwater infrastructure to handle the volume of water. Bare ground, which absorbs rainwater, was saturated by previous storms and couldn’t soak up the rainfall, he said.
“The rain fell with such intensity it couldn’t get into the ground,” Montalto said. “Roadways are designed to drain to the edges. If you get intense precipitation there is nowhere (for water) to go.”
Nationally, the country’s stormwater infrastructure got a D grade from the American Society of Civil Engineers annual infrastructure report card this year. Annually, from 2004 to 2014, flooding alone cost communities an average of $9 billion in direct damages and resulted in 71 deaths, the report found.
“In the northeast, we have infrastructure that was designed 60 to 100 years ago, Montalto said. “It’s outlived its life and is need of an upgrade.”
How to upgrade it is the challenge for engineers.
Existing storm drains and sewers were not designed for a storm of Ida’s magnitude, which was considered a 100-year-storm, said Michel Boufadel, a professor in New Jersey Institute of Technology’s Civil and Environmental Engineering department.
“Typical stormwater culverts and structures are designed for the 10-year storm or even the 2-year storm, where the amount of rainfall could be 6 inches (10-year storm) or 4 inches (2-year storm),” he said. “Therefore, it is no surprise that they got overwhelmed.”
Extreme storms such as Ida must be considered when building new drainage systems and development, said Marouane Temimi, an associate professor in Stevens Institute of Technology civil, environmental and ocean engineering department.
“The existing infrastructure was designed using past measurements of rainfall events. As the climate change and the frequency of the extreme increases, the past is no longer a good guide for the future,” he said. “We have to take into account the increasing frequency of extreme events in the region due to climate change.
Does that mean storm drains and sewers systems all need be larger? That might not be a universal solution.
Upgrading existing drainage systems to store stormwater is an option to just building bigger systems to handle the extreme events, Temimi said. One idea is to have underground drainage systems that live above ground detention ponds to hold the excess water and let it slowly drain off.
“It is possible to upgrade the existing (systems) and make it ‘smarter’ by adding sensors and hydraulic devices like pumping stations, gates in the network that can help us optimize the retention capacity of the drainage system,” he said.
Development also plays a role in worsening floods. Rainwater runoff moves faster over paved and built-up surfaces than bare ground, sending it in to rivers faster than it would normally flow, Temimi said.
“To avoid seeing our streets and basements flooded, we can store stormwater as long as possible in the pipelines, underground or aboveground tanks, and other locations in the watershed,” Temimi said.
Designing other solutions is part of the challenge, Montalto said. An option is using portable barriers to channel floodwaters.
Another possibility is designing streets to augment drainage systems and help carry off some stormwater, a concept being done in Copenhagen, Montalto said. Streets are being used to carry four inches of stormwater away from homes and buildings, he said.
Having more green space to allow water to be absorbed could be part of a solution.
“One could always advocate for greening and for allowing percolation of water in the ground, but these would not mitigate a 100-year storm,” Boufadel said. “We might need to think about allowing certain areas to flood to protect other areas, but this could lead to major dilemmas in terms of environmental justice and equity.
The state Department of Environmental Protect has bought up homes in harm’s way in flood-prone areas through a program called Blue Acres.
Under that program homeowners in flood zones voluntarily sell their homes to the state, which demolishes the house. The state has demolished 705 buildings and has funding to buy 1,188 properties and has offers out to owners of 1,126 homes, said Caryn Shinske, a DEP spokeswoman..
Between May 2013 and now, 830 families accepted buy-out offers. Closings have taken place to buy 770 properties in 20 municipalities spanning the state from Cumberland to Bergen County, she said.
