Re-imagining sea level rise is more than an academic exercise

From An Inconvenient Truth to the present, much of our understanding of climate change has come in the form of stark graphs and scientific models depicting CO2 levels and global temperature increases, global temperature rises and rising sea levels. Surely, the graphs and models are important, but they tend to make climate change feel abstract, or removed from our daily experiences.

But climate change – or one aspect of it – sea level rise, is not abstract at all, especially not for residents of St. Petersburg. The consequences of sea level rise show up in our newspapers, on our televisions, in our backyards and in the rusting pipes beneath our homes, explained Gary Mitchum, Professor and Associate Dean at the USF College of Marine Science, and Claude Tankersley, Public Works Administrator at the City of St. Petersburg.

Mitchum, a scientist, and Tankersley, a practitioner, joined forces to explain and re-imagine the tangible consequences of sea level rise – sunny-day flooding and extreme rainfall – in the latest installment of the St. Petersburg Downtown Partnership and Kate Tiedemann College of Business’ ongoing Sunny Side Up Lecture Series.

The duo started working together when Mitchum reached out to Tankersley to see if his research on predicting extreme high tides (which peak twice each year) could help the City of St. Petersburg dealing with the sunny-day/high tide flooding seen in many low-elevation neighborhoods in St. Petersburg. Fifty percent of St. Petersburg’s population lives below 10 feet of elevation, Mitchum explained. So even minor rises in sea level can pose major problems.

According to Mitchum, sunny day or high-tide flooding is becoming more frequent, and though the costs may be small with each event, they can end up cumulatively more expensive than a large event like a major hurricane. “It’s the ‘death by a thousand cuts’ problem,” Mitchum explained.

Mitchum and Tankersley began to look at how Mitchum’s research could help plan for and predict some of the costs of those events, like planning overtime for city employees.

But it isn’t the sunny day and high-tide flooding that has caused the most headaches for the city, Tankersley explained. Of the numerous consequences that climate change has for public infrastructure in St. Petersburg, extreme rainfall events are actually the most destructive. Extreme rainfall events have increased 300 percent nationwide since the 1960s, Mitchum said. Yet most of the piping in St. Petersburg was designed to handle rainwater rates from the 1950s and ’60s.

“When trying to drain water off, the rate at which you can drain it depends purely on the diameter of the pipe,” said Mitchum. “We put in pipes in the ’50s and ’60s based on the rain rates we were getting then, and the rain rates that we’re getting now are much higher. Even if we’re getting the same amount of rain – the same number of cubic feet – we just can’t move it fast enough.”

How those pipes move water also has implications for the city’s wastewater treatment systems. Most of the highly publicized and controversial sewer overflows in the City of St. Petersburg in 2015-2016 were due to stormwater and rainwater getting into the wastewater system, said Tankersley. With every wastewater treatment plant at less than 10 feet of elevation, even the six inches of sea level rise St. Petersburg has experienced since World War II has led to impacts on St. Petersburg’s sewer system.

“Our wastewater systems have been around for about 100 years. When they were first put in, the intent of the wastewater systems was not to treat the water. We didn’t know how to do it back then, but we knew that we wanted to get the wastewater away from the human population,” Tankersley explained. “How do you get wastewater away from people? You move it by gravity; water runs downhill.” Before the time of wastewater treatment, the wastewater would go directly into the bay, which is why all of St. Petersburg’s wastewater treatment facilities are located right next to the water. They could be moved to higher elevations, Tankersley said, but such a move would pose other problems, like building pump systems and ensuring power to those pump systems in the case of a power outage or major hurricane.

Sea level rise poses a number of other problems for the city as well. Sea walls are particularly difficult for the city to address, said Tankersley. St. Petersburg is home to more than 60 miles of coastline. While there is sea wall along most of that, the vast majority of the sea walls in St. Pete are privately owned. “We could raise the sea walls throughout the city, but we’ve got to get everybody to do it,” he explained. “You could have a neighborhood where 99 out of a hundred raise their sea walls, and then there’s that one person who doesn’t want to, can’t afford to, or doesn’t realize it, if that one person doesn’t raise their sea wall and you’ve got that gap, it doesn’t do any good.”

Rising seas also affect infrastructure like roads and buried utilities. “One thing most people don’t think about is that sea level and your groundwater table are connected,” Tankersley said. “You may not be close to water, you may be a mile or two away but as the sea level rises so does the water under your home.” That rising groundwater then surrounds buried utilities, often made out of metals, that were designed under the assumption that they would remain dry. “Now they’re exposed to water,” he explained. “Water and metal means rust.”

That higher groundwater table combined with higher intensity rainfalls also has major consequences for roads. It deteriorates the road base, which lies underneath the pavement and is composed of compacted rock or limestone. “When the roads were designed and the water table wasn’t near the base, it was no big deal,” said Tankersley. “But now you’ll notice after a heavy rain or a big storm, there are more potholes -that’s because the road base is deteriorating.”

Tankersley pointed to numerous initiatives and programs that the City of St. Petersburg is undertaking to fortify against climate change and sea-level rise, including the creation of the Office of Sustainability & Resiliency, the Integrated Sustainability Action Plan, The Coastal High Hazard Plan and the STAR Communities assessment.

In the end, Tankersley and Mitchum agree, there are two responses: retreat, or adapt and fortify. “The cost of action is billions of dollars, but the cost of inaction is even more,” Tankersley said.