[Note that this article is a transcript of the video embedded above.]

On September 28, 2022, Hurricane Ian made landfall on the western coast of Florida as a Category 4 storm, bringing enormous volumes of rainfall and extreme winds to the state. Ian was the deadliest hurricane to hit Florida since 1935. Over 100 people died as a result of flooding and over 2 million people lost power at some point during the storm. The fierce winds that sucked water out of Tampa Bay, also forced storm surge inland on the south side of the hurricane, causing the sea to swell upwards of 13 feet or 4 meters above high-tide. And that doesn’t include the height of the crashing waves. One of the worst hit parts of the state became a symbol for the hurricane’s destruction: the barrier island of Sanibel off the coast of Fort Myers. The island’s single connection to the mainland, the Sanibel Causeway, was devastated by Hurricane Ian to the point where it was completely impassable to vehicles. Incredibly, two weeks after hiring a contractor to perform repairs, the causeway was back open to traffic. But this fix might not last as long as you’d expect. How did they do it? And why can’t all road work be finished so quickly? Let’s discuss. I’m Grady, and this is Practical Engineering. In today’s episode, we’re talking about the Sanibel Causeway Hurricane Repairs.

What is a causeway anyway? You might think the only two options to get a road across a body of water are a bridge or a tunnel, but there’s actually a third option. You can build an embankment from compacted soil or rock that sits directly on the seabed and then construct a roadway on top of that. A path along reclaimed land like this is called a causeway, and the one between Fort Meyers and Sanibel Island in Florida was first built in 1963 and rebuilt in 2007. But, a causeway has a major limitation compared to a bridge or tunnel: it doesn’t allow crossing of maritime traffic because it divides the waterway in two. So, the Sanibel Causeway has some bridges. And actually, for a structure called a causeway, it’s mostly bridges, three to be exact. Bridges C and B are long, multi-span structures that sit relatively low above the water. Bridge A, closest to the mainland, is a high-span structure to allow for tall sailboats to pass underneath. Islands 1 and 2 are the actual causeway parts of the causeway where the road sits at grade (or on the ground). Overall, the causeway is about 3 miles or 5 kilometers long, carries over three million vehicles a year, on average, and, critically, is the only way to drive a vehicle on or off Sanibel Island, which is home to about 6,000 people.

Each of the two causeway islands serves as a county park with beaches and places for fishing. The islands aren’t natural. They were built up in the 1960s by dredging sand and silt from the bay and piling it up above the water level. It’s pretty easy to see this on the aerial photos of the islands. They really are just slender stretches of dredged sediment sitting in the middle of the bay. But, they didn’t pile the sediment that high above the water. The top of the roadway along the islands is only around 7 feet or 2 meters above sea level. And here’s the thing about sand and silt. If you look at the range of earthen materials by particle size, the large ones like gravel and even coarse sand don’t erode quickly because they’re heavy, and the tiny ones like clay don’t erode quickly either because they’re sticky (they have cohesion), but right in the middle are the fine sands and silts that aren’t heavy or sticky, so they easily wash away. The storm surge and waves brought on by Hurricane Ian breached both of the causeway islands, violently eroding huge volumes of sand out to sea and leaving the roadways on top completely destroyed. But that wasn’t the only damage.

In between the island sections of roadway and the bridges are the approach ramps: compacted soil structures that transition from the low causeway islands up to and down from the elevated sections. Instead of using traditional earthen embankments as the approaches for each bridge, the 2007 project included retaining walls built using mechanically stabilized earth, or MSE. I have a few videos about how these walls work you can check out after this if you want to learn more. Basically, reinforcing elements within the soil allow the slopes to stand vertically on the bridge approaches, saving precious space on the small causeway islands and reducing the total load on the dredged sand below each approach. Concrete panels are used as a facing system to protect the vulnerable earthen structures from erosion. But, you know, these are meant to protect against rainfall and strong winds, not hurricane force waves and 10 foot storm surge. With the full force of Hurricane Ian bearing down on them, three of the causeway’s approach ramps were heavily damaged. The one on the mainland side, and the ones on the north side of each causeway island. The bridges themselves largely withstood the hurricane with minimal damage, thanks to good engineering. But, with the approaches and causeway sections ruined, Sanibel Island was completely cut off from vehicle access, making rescue operations, power grid repairs, and resupplies practically impossible.

Within only a few days of the hurricane’s passing, state and county officials managed to pull together a procurement package to solicit a contractor for the repairs. On October 10, they announced their pick of Superior Construction and Ajax Paving and their target completion date of October 31st. Construction crews immediately sprang into action with a huge mobilization of resources, including hundreds of trucks, earth moving machines, cranes, barges, dredges, and more than 150 people. Major sections of the job were inaccessible by vehicle, so crews and equipment had to be ferried to various damaged locations along the causeway. The power was still out in many places, and cell phone and internet coverage were spotty. Even coordinating meals and places to sleep for the crew was a challenge.

For the most part, the repairs were earthwork projects, replacing the lost soil and sand along the causeway islands and bridge approaches. A lot of the material was dredged back from the seabed to rebuild each of the two islands, but over 2,000 loads of rock and 4,000 tons (3,600 metric tons) of asphalt were brought in from the mainland. Just coordinating that many crews and resources was an enormous challenge both for FDOT and the contractor. Both made extensive use of drones to track the quantities of materials being transported and placed and to keep an eye on the progress across the 3-mile-long construction site. Progress continued at a breakneck pace at each of the damaged areas of the causeway to bring the subgrade back up to the correct level. Once the eroded soil was replaced, all the damaged sections were paved with asphalt to provide a durable driving surface. With the incredible effort and hard work of the contractor and its crews, the designers, FDOT and their representatives, emergency responders, relief workers, and many more, the causeway was reopened to the public on October 19th, a short 15 days after the project started and well ahead of the original estimated completion date.

You might be wondering, “If they can fix a hurricane-damaged road in two weeks, why does the road construction along my commute last for years?” And it’s a good question, because you actually sacrifice quite a lot to get road work done so quickly. First, you sacrifice the quality of the work. And that's not a dig on the contractor, but a simple reality of the project. These temporary repairs aren’t built to last; they’re built to a bare minimum level needed to get vehicles safely across the bay. Look closely and you won’t see the conveniences and safety features of modern roadways like pavement markings and stripes, guard rails, or shoulders.

These embankments constructed as bridge approaches are also not permanent. Something happens when you make a big pile of soil like this (even if you do a good job with compaction and keeping the soil moisture content just right): it settles. Over time and under the weight of the embankment, the grains of soil compress together and force out water, causing the top of the embankment to sink. But the bridge sits on piles that aren’t subjected to these same forces. So, over time, you end up with a mismatch in elevation between the approach and bridge. If you’ve ever felt a bump going up to or off a bridge, you know what I mean. In fact, this is one of the many reasons why you might see a construction site sitting empty. They’re waiting for the embankments to settle before paving the roadway. Oftentimes, a concrete approach slab is used to try and bridge the gap that forms over time, but I don’t see any approach slabs in the photos of the repair projects. That means it’s likely these approaches will have to be replaced or repaired fairly soon. In addition, the slopes of the approaches are just bare soil right now, susceptible to erosion and weathering until they get protected with grass or hard armoring.

The other sacrifice you make for a fast-track project like this is cost. We don’t know the details of the contract right now, but just looking at all the equipment at the site, we know it wasn’t cheap. It’s expensive to mobilize and operate that much heavy equipment, and the rental fees come due whether they sit idle or not. It’s expensive to pay overtime crews to maintain double shifts. It’s expensive to get priority from material suppliers, equipment rentals, work crews, fuel, et cetera, especially in a setting like a hurricane recovery where all those things are already in exceptionally high demand. And, it’s expensive to keep people and equipment on standby so that they can start working as soon as the crew before them is finished. Put simply, we pay a major premium for fast-tracked construction and an even bigger one for emergency repairs where the conditions require significant resources under high demands.

Of course, it wasn’t just the roadways damaged on Sanibel Island. The power infrastructure and many many buildings were damaged or destroyed as well. And it wasn't just Sanibel Island affected, but huge swaths of coastal Florida too (including nearby Pine Island that had an emergency bridge project of its own). There’s a long way to go to restore not just the roadway to Sanibel Island, but also the island itself. And that will involve a lot of tough decisions about where, how much, and how strong to rebuild. After all, Sanibel is a barrier island, a constantly changing deposit of sand formed by wind and waves. These islands are critical to protecting mainland coasts by absorbing wave energy and bearing the brunt of storms. In fact, many consider barrier islands to be critical infrastructure, but development on the islands negates that critical purpose. That doesn’t mean the community doesn’t belong there; nearly every developed area is subject to disproportionate risk from some kind of destructive natural phenomenon. But it does obligate the planners and engineers involved in rebuilding to be thoughtful about the impacts hurricanes can have and how infrastructure can be made more resilient to them in the future.