How something called a 'marine mattress' is crucial for fortifying the Sanibel causeway

After Hurricane Ian slammed Southwest Florida on Sept. 28, 2022 and caused catastrophic damage to the iconic Sanibel causeway, there was unprecedented urgency to get the 3-mile stretch of road to be functional again.

In other words, providing essential vehicle access from the island to the Lee County mainland at Punt Rassa.

Remarkably, thanks to emergency repairs opening the causeway again took only days and not months. Sections of the causeway that were washed away by Ian's historic storm surge were fixed marking the beginning of what will be a lengthy comeback.

Now, fast forward 18 months.

Like other mega restoration projects, the causeway work is happening in phases with work is being done to fortify the structure so if another powerful Category 4 storm like Ian comes along the causeway will have a much better chance of withstand punishing wind and waves.

According to the Florida Department of Transportation (FDOT), resiliency features are being incorporated into the Sanibel Causeway restoration. Recently, on its Facebook page, FDOT posted a photo that caught our attention − the placement of what are known as marine mattresses. These mattresses are one component of making the causeway more resilient.

We connected with FDOT to learn more about this fascinating aspect of the restoration project.

Sanibel causeway restoration: A closer look at a unique resiliency feature

Q. What is a marine mattress?

FDOT: The marine mattresses are rock-filled geotextile mattresses. They are placed between the sheet pile walls and the roadway to help diffuse wave energy. They are also used anywhere else on the project where there is a need to prevent shoreline erosion.

Q. When did this phase of the project begin?

FDOT: The Sanibel Causeway restoration has been two projects that have run sequentially with overlap.

Emergency repairs were completed October 2022.

Permanent repairs began immediately following restoration of island access.

Installation of marine mattresses began in late February 2024, but teams had been filling the mattress forms since the summer of 2023. The stockpiles are visible on the causeway islands.

Q. How many marine mattresses are being placed?

FDOT: 180,000 square feet of marine mattresses are being placed.

Q. Where are the marine mattresses made? Where do they come from?

FDOT: We are using the Baselok marine mattress system out of Houston, Texas.

The empty geotextile mattress frames are filled and closed by onsite teams.

Q. Are there any more details on the process of placing them and how it is done?

FDOT: It’s a pretty simple process – an empty mattress is placed within a frame that holds it open for filling.

Spacers are placed within each mattress cell and are removed when the cell is about halfway full of rocks. Once each cell is completely full, the mattress is laced shut, removed from the frame and moved to a storage area until it is ready for final placement.

This article originally appeared on Fort Myers News-Press: When will the Sanibel florida causeway restoration be completed