Sanibel’s Short Term Solution Against Erosion:
Beach renourishment is common in places with significant sand movement. Since Sanibel Island is a place with a large amount of longshore drift, sand is constantly being transported in a north to south direction. On top of this, rough waves and storms can erode substantial portions of sand from the beach. As a result, every 9-10 years, the City of Sanibel Island has conducted beach nourishment projects. During this process, sand is sucked off of the sea floor a couple of miles off-shore and loaded into a large container. This sand is then transported to the shore, where it is pumped through large pipes. Bulldozers are used to spread the sand over the beaches. Beach replenishment in Sanibel is not a sufficient long-term solution. Over a few years, erosion and longshore drift continue to move sand away from the beach or to other beaches entirely. Renourishment also leads to the creation of unnaturally large sand bars, disrupting the oceanic environment.
Image 1: A bulldozer near the shoreline
A Long-term Solution:
Living shorelines maintain the balance of protecting the beach from erosion and promoting an ecologically sustainable solution. Lighthouse Beach Park has become a prototype of this type of shoreline. The City of Sanibel has used a combination of plants, aquatic vegetation, and rock rip-rap to armor the shoreline from harsh weather, tides, and current. Mangroves in particular help reduce sand erosion by anchoring in sediment using their root systems. Mangroves are also a natural barrier against the surf. During large storms, tides, and hurricanes, mangroves can slow down water flow. Seagrasses are also a common form of aquatic vegetation utilized for living shorelines. They are common in bays and prevent salt marshes from eroding by dissipating wave energy.
Image 2: Living shoreline infographic by NOAA
Parts of a Living Shoreline:
Image 3: Living shoreline profile
Logging Tasks:
- At the GZ, you will be standing on a walkway and observing one of Sanibel’s first implementations of a living shoreline. Do you spot any structures, plants (such as mangroves or seagrass), etc. that help prevent this part of the island from erosion?
- Utilizing Image 3 and what you notice at the GZ, what part of the living shoreline are you standing on?
- Walk down to the beach. Do you observe any significant sand erosion?
In Southwest Florida, common signs of erosion include small-scale “cliffs” of sand like this:
- Make a final conclusion based on what you’ve learned in the description and your observations at the GZ. Is this prototype of a living shoreline at the GZ effectively preventing this area from coastal erosion? Should more measures be taken to stave off erosion?
- As of June 2019, earthcaches now contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. Please post this in your log.
Sources:
https://www.vims.edu/ccrm/outreach/living_shorelines/index.php
http://www.seafriends.org.nz/oceano/beacheng.htm
https://sanibelrealestateguide.com/sanibel-beach-erosion-prevention/
https://www.habitatblueprint.noaa.gov/living-shorelines/leading/
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