WEIRd Jetty Earthcache EarthCache
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The technical definition of a jetty is: any of a variety of engineering structures connected with river, harbor, and coastal works designed to influence the current or tide or to protect a harbor or beach from waves. If you have spent any time around the water then you have probably seen one, or even walked out onto one.
Jetties are built along coastal waters for one main reason: to interrupt the normal movement of sediments along the coast caused by waves, currents and tides. That being said, the two main practical applications are meant to perform this task to opposite ends. Jetties built perpendicular to the coast (i.e., those piles of rocks that stick straight out into the surf from the beach) are meant to catch the sediment in order to retain or widen the beach. On the other hand, jetties built on either side of an inlet are meant to reduce the amount of sediment deposited in the channel that could hamper navigation. What you see before you is the northern half of the Masonboro Inlet Jetty. It is the latter type of jetty - meant to keep the inlet from being clogged by sand and sediment.
Depending on the height of the tide, the first 1000' of the jetty may be completely under water - this is by design. This is known as a Weir jetty (hence the cache name). The Weir section, which is typically less than 1000' long, is a depressed region of the jetty that permits waves and currents to carry sediments to a deposit zone located in the lee of the weir. In other words, it allows the sand and sediment to settle in a particular spot - in this case, the area to the south of the weir section (from your perspective, this is to the right of the jetty) - rather than wherever it wants to.
Masonboro Inlet has been open continuously since 1733 - however, in 1909 it was actually located 4000' south of its present location. To stabilize the location of the inlet and reduce the need for dredging, the north jetty was built in 1965 using the weir design. It has worked extremely well, as the channel has only needed to be dredged every 3 to 4 years.
To log this EarthCache, please email answers to the following (no answers in your log, please):
- Approximately how much of the weir section, if any, was above the water when you visited?
- Near the posted coordinates is a sign - what advice does it give regarding the jetty?
- Based on what you know about this weir jetty, can you surmise which way the coastal current runs on this stretch of the beach?
- Although optional, this is a terrific picture spot, so posting pictures with your Found It log is always welcome and encouraged.
Additional Hints
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