Understanding the causes of erosion on Gasparilla Island and other beaches helps us understand how to respond effectively to it.
In order to fix a problem, you must know what causes it. This applies to coastal erosion in spades. But there's no single cause for sand moving away from your coastline.
Erosion is like other "natural" occurrences such as fires, tornadoes, hurricanes and earthquakes - it lands on our collective radar only when it begins to impact people and their property. Erosion happened once again on Gasparilla Island right after Tropical Storm Debby hit June 27.
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So what causes erosion? Here are some of the agents, and what can be done about them:
Littoral transport: Sand moves along the coastline, pushed by waves and tides. When more sand leaves than arrives, the beach erodes. This can be addressed by putting more sand back into your system the right kind of sand, in the right places, at the right time, sometimes with the right assistance to help it stay in place longer.
Sea level rise: When the level of the sea rises relative to the land, shorelines retreat and beaches erode to keep up with the rising sea. Beaches will actually rise to match the level of the rise of sea level but sand is lost to the offshore in the process. The good news is that the rate of sea level rise is slow and small amounts of sand added at regular intervals can counter the effects of sea level rise.
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Ken or Kate Gooderham, American Shore & Beach Preservation Association executive directors, can be reached at (239) 489-2616.
Coastal structures: In the case of jetties and groins, these physically reduce the normal flow of sand along a shoreline, often capturing more here but keeping less from going there. In the case of seawalls and revetments, these often replace the sandy beach in protecting upland infrastructure but may make it impossible for sand to accumulate in front of them due to higher wave action and scour. After an era when all structures were deemed bad, coastal experts now suggest a more nuanced approach involves realizing structures as part of a larger engineered design can serve a purpose to anchor beaches and address hot spots.
Inlets: Sand can be intercepted by coastal inlets and retained by jetties or deposited by tides and currents in shoals. Bypassing can move sand across the coastal opening, or shoals can be scooped up and put on the downdrift beach to allow the sand to continue its natural migration.
Subsidence: Not a common issue but where it comes into play it has a huge impact (think the Louisiana Mississippi River Delta region). Here, the land is sinking due to compaction of deltaic muds exacerbated by extraction of oil and gas. Diversion of sediment from rivers as well as dredge and fill projects can counteract these processes.
There are other aspects to erosion too numerous to detail here. Suffice it to say that coastlines are highly dynamic environments with many forces - natural and man-made alike - able to have a significant impact. Understanding the causes of erosion is essential to understanding how to respond to it in a way that engenders more harmony between the coast and the people who want to enjoy it for a lifetime.
Ken or Kate Gooderham, American Shore & Beach Preservation Association executive directors, can be reached at (239) 489-2616.
