At the Oct. 1 Sanibel City Council meeting, City officials explained in depth how Hurricane Helene’s approximate 5-foot storm surge caused flooding across the island.

Prior to Helene, which passed about 150 miles west of the islands on Sept. 26, the City opened the island weirs.

“One of the major questions we’re getting a lot of is, ‘Why didn’t you lower the levels before the storm?’ The truth of the matter is we opened the weirs for three or four days beforehand,” said City Engineer Ossin Dolley.

The island’s weirs, located at Tarpon Bay Road and at Beach Road, are structures that help the City achieve surface water management as mandated by the Sanibel Plan — the comprehensive land use plan.

“Our key objectives in managing surface water here on Sanibel are to reduce extreme flooding in developed areas and to use our surface water management as one of several tools for our undeveloped areas to encourage and support wetland communities and native wildlife habitat,” said Holly Milbrandt, Director of Natural Resources.

Dolley played videos that showed how the storm surge overtopped the weirs with back flow of salt water for more than 19 hours due to Helene.

He then explained how it would take days for the surge to drain back out through the open gates of the weirs.

The SCCF Marine Lab provided data and graphs that helped illustrate water levels at the weirs and impacts of Helene.

SCCF CEO James Evans spoke during public comment at the council meeting in support of how the City handled the impacts of Hurricane Helene.

“As you can see from the data that was presented, this was a surge event, not a rainfall driven stormwater event,” said Evans. “The surge from the Gulf and the bay overwhelmed the system with water, driving water into the slough and elevating water levels.”

He also emphasized the challenges posed prior to Helene’s arrival.

“The City was very proactive in lowering water levels prior to the storm, but could only lower as much as they could given the record rainfall and the super moon tides that we experienced the week prior where docks were underwater in the bay,” he said.

Evans also addressed some comments made on social media regarding the reason for the inland flooding.

“Despite the misinformation that’s being posted on social media, the City and SCCF are not holding water levels higher on the island to convert the island from woody vegetation to marsh grass,” he said.

In the opening of her presentation, Milbrandt underscored the value of the island’s 1,600 acres of interior wetlands and the Sanibel River or Slough.

“An invaluable resource to the island-wide natural drainage system is the interior wetlands. This 3,500-acre depression in the central area of the island…plays an important role in terms of stormwater storage during both high frequency as well as more intense storms,” she said, quoting the Sanibel Plan.

Since Hurricane Ian, SCCF has been removing a lot of dead woody vegetation killed by storm surge, primarily because it’s vegetation that can no longer grow in low-lying areas because of the high salt content in the water.

“Our work has actually created more stormwater capacity in the low-lying swales in those interior wetland areas. We’re not advocating for water levels to be increased to support marsh grass,” said Evans.

He added that SCCF supports the City and the work that they do to prevent flooding in our homes and businesses.

“If warranted, SCCF would support an independent engineering assessment by the City to evaluate the City’s actions and how we can optimize stormwater management to protect our residential properties and our businesses from flooding,” he added.

Incremental sea level rise, estimated at eight inches since 1965, is also making it more challenging to drop water levels during these storm events. Higher sea levels reduce our ability to drain stormwater from the island. However, having 70 percent conservation lands on the island helps mitigate that.

“I know when we start talking about wetlands and water and flooding that it might be tempting to think that because of the amount of conservation land that we have and because of the protection of large areas of wetlands on Sanibel, that that hurts us,” said Milbrandt. “But it really is helpful. That is a tremendous part of our stormwater drainage infrastructure on Sanibel and we manage it both in a natural function and then as well as part of a formal stormwater drainage system.”

Captiva also experienced a significant storm surge, with flooding and sand on Captiva Drive.

Below are more images from the City officials’ presentation at the City Council meeting.

Click here to watch the meeting on Facebook Live. The stormwater discussion begins at 20:30.