Kill the South Jetty Extension Project
Mike Clancy
(This article appeared in the Daytona Beach News Journal in February of 2012)
Although I live in Northern California, the proposed South Jetty Extension Project at Ponce de Leon Inlet is of great interest to me. I grew up in New Smyrna Beach and began surfing at the Inlet in the mid-1960s, and I return there often to surf with my fellow Smyrna Surfari Club members.
I watched the construction of the jetties in the late 1960s, and like many local residents was dismayed as the project failed to meet its goals. Considering the cost to taxpayers, it was disheartening to see approximately 2600 feet of the south jetty disappear under sand, and thus have no impact on navigability of the Inlet, as the sand simply overran the jetty and followed it seaward. Today, only about 100 feet of the original 2700-foot south jetty extends into the ocean.
More than 40 years after construction of the jetties, the Inlet remains a relatively dangerous waterway, as buildup of a sandbar on the south side of the Inlet forces boats into a narrow channel adjacent to the north jetty that is subject to strong tidal currents and choppy waves. The South Jetty Extension Project proposed by the Army Corps of Engineers would attempt to solve this problem by extending the south jetty another 900 feet into the ocean at a cost of approximately $15 million. The Army Corps proposal assumes that the sandbar on the south side of the Inlet is produced by waterborne transport of sand. I think this assumption is wrong and that an additional 900 feet of jetty will have no more impact on the safety of the Inlet than the original 2700 feet had.
I believe there are two long-term processes at work in the Inlet that have nothing to do with the south jetty, but control the width of the navigable channel and thus the safety of the Inlet. The first is the persistent northwestward migration of sand driven into the Inlet from Smyrna Dunes Park by the prevailing southeasterly winds. This northwestward windborne sand migration is demonstrated by its burying of the south jetty, and is clearly the source of sand for the sandbar on the south side of the Inlet. The second process is the scouring of sand away from the northern edge of the sandbar due mainly to strong tidal currents flowing in and out of the Inlet through the channel.
In the absence of tidal currents, the northwestward windborne sand migration would eventually close off the Inlet. In the absence of this sand migration, the tidal currents would maintain a wide and safe channel. With both processes at work, a balance is maintained, with the sand transported into the sandbar by the winds balanced by the sand scoured away from the bar by the tidal currents. If the northwestward windborne sand migration increases over a long period of time, the sandbar encroaches farther into the Inlet. This narrows the channel, which causes the speed of the tidal currents in the channel and their resulting scouring effect to increase until the northward encroachment of the sandbar is halted and balance is reestablished. If the northwestward windborne sand migration decreases, the opposite effects occur until the balance is again reestablished. Sand is continually replenished in the Smyrna Dunes Park source region through the normal process of building dunes from sand washed ashore on beaches, with some of the sand scoured from the sandbar in the inlet eventually finding its way back into the park to complete a full cycle in this very dynamic environment. I think this simple description captures the key forces at play in the Inlet and clearly shows that extension of the south jetty would not have the desired effect.
Google Earth image of Ponce de Leon Inlet, with annotations indicating windborne sand migration into the Inlet from Smyrna Dunes Park and region of tidal scouring of the resulting sandbar. The extension of the south jetty proposed by the Army Corps of Engineers is shown in red.
Finally, the proposed 900-foot eastward extension of the south jetty would degrade surfing conditions at the surf spot adjacent to the jetty, as it would block waves coming from a northeasterly direction. This is not a trivial consideration. This surf spot is widely regarded as one of the best on the entire East Coast, and its existence led to New Smyrna Beach being named one of the Top 10 American Surf Towns by Surfer Magazine. In addition to providing a significant recreational outlet for all of Central Florida, the Inlet surf spot supports a local surfing industry that pumps millions of dollars into the Volusia County economy.
The South Jetty Extension Project would have no impact on the safety of navigation through the Inlet, degrade a tremendous recreational resource, and damage an important component of the local economy. It should be killed.
Mike Clancy is the former Technical and Scientific Director of the U.S. Navy’s Fleet Numerical Meteorology and Oceanography Center in Monterey, CA, and a recipient of the Navy’s highest civilian award.