August 14, 2012
Contact: Ken or Kate Gooderham, ASBPA executive directors -- (239) 489-2616
Harry Simmons, ASBPA president -- (910) 200-7867
What causes erosion?
Understanding its causes helps us understand how to respond effectively to it
In order to fix a problem, it usually helps to know what causes it. This applies to coastal management, of course, particularly when the issue of erosion. In order to address coastal erosion, you need to know what’s behind it – since there’s no single cause for sand moving away from your coastline.
Erosion is like other “natural” occurrences such as fires, tornadoes, hurricanes, earthquakes and more – it lands on our collective radar only when it begins to impact people and their property. When it happens out in the middle of nowhere, nobody notices. When it happens where people live and work, it gets noticed – a lot.
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.
- 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… realizing that 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.
Of course, 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 manmade 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 day, a week, a month or a lifetime.
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ABOUT ASBPA: Founded in 1926, the ASBPA promotes the integration of science, policies and actions that maintain, protect and enhance the coasts of America. For more information on ASBPA, go to www.asbpa.org, facebook or www.twitter.com/asbpa.