It could cost more than $4.7 billion to fortify Tampa Bay’s most important roads from the flooding that might come during a major storm in 2045, according to a draft study from local planning agencies.
Investing now, planners say, is prudent and potentially cheaper than waiting for a hurricane to do damage. It would harden key roadways like the approaches to the Gandy Bridge and part of U.S. 19 in Pasco County.
“Our big goal with this report was to draw attention to the risk of not making some basic investments to reduce our road network’s vulnerability,” said Beth Alden, executive director of the Hillsborough Metropolitan Planning Organization. “What are the chances that we are not going to be hit by a Category 3 storm between now and 2045? ... I’m not willing to roll the dice.”
The planners modeled the most severe flooding from a Category 3 hurricane with high sea level rise in 2045, as well as a storm that would drop nine inches of rain in one day. In such scenarios, models show, streets could temporarily look like rivers in downtown St. Petersburg and downtown Tampa. Across Hillsborough, Pinellas and Pasco counties, hundreds of miles of roads would be vulnerable to flooding.
The effort, called the “Resilient Tampa Bay: Transportation Pilot Program Project,” was supported by a $250,000 grant from the Federal Highway Administration, Alden said. It was part of the planning process for local agencies that handle transportation and included officials from Pinellas, Pasco, the Tampa Bay Regional Planning Council and consultants.
They focused on a sea level rise projection from the National Oceanic and Atmospheric Administration that calls for about a foot more water by 2040 — not the most extreme, but a high estimate. The report used a model also from the agency that relies on hurricane simulations to show the greatest potential surge for different categories of storms.
The point was to look at extreme weather, but those involved said the scenarios are plausible for Tampa Bay, with a geography that puts it at serious risk to storm surge and flooding.
“To ignore the weather science will only lead to the potential failure of the transportation network,” said Sean Sullivan, executive director of the Tampa Bay Regional Planning Council. “You can always put things off and kick the can down the road. The problem is at some point that can is going to explode.”
Officials simulated a day with nine inches of rain based on historical data, which showed the biggest one-day storm in Tampa Bay dropped 11.45 inches in 1979. As recently as 2015, a multi-day rain event dumped between four and 11 inches.
Improvements described in the report vary from raising the streets, at a cost of as much as $16 million per mile, to planting vegetation that could combat erosion for less than $16,000 per mile. The goal is to keep water off the roads, or to harden the pavement so it is not scoured in a flood.
Among the ideas is raising parts of the approaches to the Gandy Bridge that models show could be inundated by a Category 3 storm. The cost? More than $70 million.
A nearly 5-mile stretch of Gulf Boulevard in Pinellas is similarly at risk, according to the report, but it is surrounded by businesses, making it difficult to widen or elevate the street. The planners suggest bolstering the natural shoreline and adding drains at a combined cost of more than $12 million.
In Pasco, part of U.S. 19 near New Port Richey could be elevated to avoid flooding, according to the planners. Such a project might have the added benefit of creating a de facto storm surge barrier for neighborhoods east of the highway. The cost could exceed $136 million.
Rodney Chatman, planning division manager at Forward Pinellas, said to tackle every issue in the county would take about $3 billion.
“It’s not like you can just work within your existing budgets to carve out an extra $3 billion to make your road network more resilient,” he said.
Planners looked for ways to make the bill less imposing by using a matrix to highlight priority roads at the greatest risk. They considered how much traffic a street carries, whether it is an evacuation route and how close it is to important service centers like hospitals. For vulnerability, they broke out flooding by levels, with the highest risk being 11 feet or more, and moderate risk being about 6 to 10 feet of inundation.
About 245 miles across the three counties are considered highly critical and either highly or moderately vulnerable to flooding, according to the report.
Alden said officials in Hillsborough would need to boost the money budgeted for stormwater by about $22 million a year for the next 20 years to address critical and at-risk roads. She said the $84 million a year spent on road surfacing, with modifications like hardening the asphalt or putting in more permeable surfaces, would need to nearly double. She hopes the report helps leaders “focus particularly on areas where there is the greatest return on investment.”
Sullivan, of the Regional Planning Council, said resilience planning will be key to securing federal funding for road projects going forward. Recovery after a storm will only get more costly, he said.
“We have a lot to protect in terms of transportation and our economy.”