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Planning Commission approves erosion control structure

By Staff | Jul 6, 2016

The City of Sanibel Planning Commission approved an application that would provide an upland installation of an erosion control structure for 100 linear feet of rip-rap material off of Bayview Drive.

The conditional use permit, as well as the development permit application, that were brought before the Planning Commission last week was a joint one between the City of Sanibel and property owners James and Karen Hall.

Roy Gibson, City of Sanibel senior planner, said it is a joint application because the property includes privately owned shoreline, as well as city owned parcel. The piece of property is located on the western end of the Bailey Beach area, also known as the Bayview Park.

A current survey of the property, the findings of progressive erosion along the area of the bay front property, as well as specific and general use requirements for erosion control structures have been addressed by Hans Wilson & Associates.

According to a staff report the property is located along San Carlos Bay, which has been experiencing ongoing beach erosion for many years due to the wake action from boats, as well as wind and wave action generated from northerly influenced weather fronts and tropical storms.

Hans Wilson, a registered engineer for Florida, said a vertical seawall holds the land and deflects the wave energy. He said the problem with deflecting the wave energy is that the incoming wave goes in two directions either up in the air, or down. When going down it begins to erode the seawall. If the wave goes up into the air it erodes the land behind the seawall.

“We wondered what we could do to minimize the impact to the shoreline and try to taper that erosion effect,” Wilson said.

Immediately offshore there is a pretty extensive sea grass bed that exists off the vertical wall. He said there is a fairly significant differential when going further offshore in the area that is mostly highly eroded because the sand is being washed offshore and covering the sea grass.

City of Sanibel Natural Resource Director James Evans said for the past six or seven months they have monitored shoreline erosion that is occurring to the west of Bayview Park in front of and adjacent to the Hall property.

He said Mr. Hall’s property, which is a very small portion of the shoreline that comes to a point in the area, has water coming around the existing seawall eroding his property, as well as the city’s adjacent property.

“We looked at ways to potentially mitigate the problem with vegetation,” Evans said, adding because of the nature of the erosion in the area, the amount of surface area between the open water and the land area is getting a lot of erosion. “We didn’t think we could address it through vegetation alone. In this case we feel that revetment with vegetation would be the best and most effective way to address the shoreline erosion in this area.”

He said their plan is to put in a plant shelf, which will provide structure for red mangroves to establish in the shoreline.

“Our plan is also to taper off with vegetation to the east from Bailey Beach Park. To the east we will also have extensive vegetation that we hope will stabilize that shoreline,” Evans said.

Wilson said they are going to be digging out the sand to get the rip rap placed down below the elevations that exist today. He said once the structure is built the sand will be placed back over the top.

Commissioner Holly Smith asked what the time factor would be after the barrier is put into the water before the mangrove starts to grow and become successful. She also asked if there is a manmade barrier that can be put up for additional protection.

“That’s one of the reasons we are planting this planter,” Evans said. “It’s going to take years for the red mangroves to establish, that’s one of the reasons why they need to be stabilized.”

Wilson said the planter is holding enough soil for the mangrove roots to become established, but the idea is to get them established outside of the planter.

In answering a question from the planning commission, Evans also addressed if other areas of the island are experiencing that type of erosion.

The city is seeing erosion along the bay side, but they do not know if it’s because of the sea level rise.

“Being a barrier island it’s something we certainly need to consider and so we will be looking at measures to help mitigate whether it is sea level rise, or erosion coming from other factors along our bay beach zone,” he said.

Evans said the idea of implementing living shorelines would incorporate the use of vegetation and oyster shells, or mangrove planters as a tool to help mitigate some of the impacts.

Areas adjacent to seawalls, he said are typically where they see a lot of erosion.

The City Council approved a budget amendment for $25,000 for this project, which has a cost share of 64 percent from the city and 36 percent from the applicant.

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