Alabama. Studying the Sand Cliffs on the Alabama/Florida Gulf Coast
A recent scarp that was more than five-feet-tall occurred on a Florida beach in Perdido Key where there are no engineered or renourished beaches.
Orange Beach, AL – (OBA®) – Whether or not the "sand cliffs" – scientifically known as scarps – are formed during what is called a neap tide is up for debate. But local beachgoers have noticed the steep embankments, some higher than five feet, seem to be more prevalent around the neap tide.
“It’s not something I’ve ever seen in the literature or heard anybody else talk about but I’m not going to tell somebody that they’re wrong if they have made that correlation,” South Alabama Professor Emeritus Scott Douglass said. “But I got to thinking that maybe there is something to it because we have such a mild coast compared to all the other ones in the U.S. We have periods where there’s just nothing happening because the waves are so small.” Douglass is a civil engineer and his area of expertise is coastal engineering.
Orange Beach Coastal Resources Director Phillip West said he doesn’t think neap tides are the cause but he’s keeping an open mind.
“I think somebody just saw a relation, saw the scarp, looked up the tide table and said, ‘oh, it’s a neap tide. It must be causing that,’” West said. “It’s not an unusual way of looking at things. But I doubt it.”
Sometimes scarping is associated with beach renourishment projects after new sands have extended the beach to reclaim what was taken in storms.
“We get those scarps quite frequently right after a beach nourishment project because the method of construction, you’re pumping sand, you’re pushing it with bulldozers, you’re doing grading but you can’t create the natural profile,” West said. “That’s not going to be the final profile because that beach has to undergo a process of equilibration. During that process when the water and wind – mostly water – are pounding that beach, that creates a lot of scarps.”
Douglass said he heard complaints from people following the renourishment projects because of the scarping that eventually occurs after new sand is added to the coastline.
“People criticize beach renourishment projects for that but there are plenty of scarps that aren’t anywhere near a renourishment project,” Douglass said. “I think scarps occur on all beaches naturally and they seem to occur more frequently on nourished beaches that haven’t had the equilibration completed.”
In fact, a recent scarp that was more than five-feet-tall occurred on a Florida beach in Perdido Key where there are no engineered or renourished beaches.
“They’ve never had a beach nourishment project over there so that’s just a natural formation I’d guess probably caused by a pretty sizeable cusp and that crescentic feature,” West said. “We call those beach cusps. For one to be that pronounced it would probably take some ideal conditions over a period of many days or weeks for that to form.”
Another factor raising West’s doubts about neap tides fomenting scarping is simply the force required to make it happen to the shore.
“A neap is the weakest tide period of the month,” West said. “The gravitational forces generally sun and the moon are opposed and at right angles somewhat. They cancel out each other’s force or minimize it. A neap tide translates into less energy and what you’re seeing is a focus of higher energy in an immediate area to have that scarp form.”
More interaction between waves and wind are needed to cut into the coastline.
“That scarp, it’s not a push of sand to form a cliff or scarp,” West said. “It’s a carving out of the upper beach. It’s not so much the tides but at high tide, that wave energy could be further up on the beach and that would exacerbate the scarp creation or facilitate it. But generally, it’s wave energy. Those long periods of groundswell and on top of that you could have wind-driven waves. It’s ideal conditions when they are coming from two different directions.”
Both men said there are noted differences in other ways between the Gulf Coast and other coastlines in the U.S. First, said Douglass, the others are subject to a wider variety of storms.
“We have periods (in the Gulf) where there’s just nothing happening because the waves are so small,” Douglass said. “You usually don't get that in the Atlantic or the Pacific because there’s always some storm somewhere out in the Atlantic or Pacific that occurred a week or two prior that’s sending waves to hit you. That’s not true in the Gulf of Mexico. There’s plenty of times I call it the Lake of Mexico typically in the summer when people would notice that related to the neap tides.”
The tide flow on Gulf coasts is just a little milder because it’s more sheltered from storms from the other side of the world.
“The Gulf’s an anomaly anyway that we only get one high and one low a day,” West said. “Most places get two highs and two lows. Also, the tidal change from low to high is also pretty mild. We just don’t get strong tides. At Perdido Pass when the tide’s moving it looks pretty impressive. It’s a very narrow body for a lot of water to pass through. It creates the garden hose nozzle effect sort of.”