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Welcome to Sebastian Inlet State Park. The Sebastian Inlet marks the border between Indian River County and Brevard County. It is one of the premier saltwater fishing spots on the east coast of Florida to catch redfish, bluefish, snook, and Spanish mackerel. Northeast swells smack into the inlet's curved north jetty creating a powerful wedge effect that surfers have dubbed “First Peak”. Surfers from around the world visit the inlet to surf First Peak and several surfing competitions are held in the park every year. On the north side of the inlet, just west of the A1A bridge is a small swim cove. The sheltered waters of the cove are especially popular with families that have young children. Two museums offer many fascinating exhibits about the area. The Sebastian Fishing Museum provides a detailed history of the fishing industry and commemorates three of Sebastian’s early families that operated fish houses. The McLarty Treasure Museum features history and artifacts from the 1715 Spanish Plate Fleet. Eleven Spanish treasure galleons sunk along the east central coast of Florida during a hurricane. Gold, silver and jewelry are still being recovered from the wrecks. Sebastian Inlet State Park has three miles of beautiful beaches along the Atlantic Ocean, a full facility campground and a boat ramp on the lagoon. Canoeing and kayaking in the Indian River Lagoon gives paddlers a chance to view young sea turtles, dolphin, manatee and a huge variety of shoreline birds.
The first known attempt to create an inlet in the vicinity of present day Sebastian Inlet was in 1885. Captain David Gibson, a turpentine baron from Georgia, organized a band of volunteers to open an inlet that would serve his land holdings on the Indian River Lagoon near Malabar. Using shovels and wheelbarrows, the volunteers dug an opening across a 260 foot wide section of the barrier island. The channel was completed by 1895 only to be closed by a Category 3 hurricane a few months later.
Over the years other individuals and government agencies attempted to create and maintain a stable inlet spending hundreds of thousands of dollars along the way. “Gibson’s Folly” eventually became Sebastian Inlet, a permanent opening about three miles north of Gibson’s first cut. The inlet would fill with sand and continue to close if it was not protected by two parallel jetties and shoreline armor like rip rap and seawalls. The north jetty is approximately 1,600 feet long and the southern jetty is about 1,200 feet. The inlet and extended jetties interrupt the normal movement of sand being carried south by Florida’s longshore current. Sand from updrift beaches is pulled into the inlet instead of moving along to more southern beaches. The sand is trapped where the inlet widens into the Indian River Lagoon and the current is slower. Sediment deposited in this area must be dredged up periodically and placed on the down-drift beach to counter erosion.
When the jetties were constructed in 1955, a district engineer for Sebastian Inlet recommended that the width of the inlet be narrowed from 600 feet to 500 feet. This would increase the velocity of the current through the inlet and reduce the need for maintenance dredging. Today the inlet is about ¾ miles long and has been cleared down to an Anastasia Rock formation which is the familiar orangish brown coquina found along Florida’s coast. Coquina is made up of mollusk shell fragments in a sand matrix cemented by calcite. The hard rocky bottom and armored sides of the inlet help stabilize the opening and also increases the rate of flow through the inlet. Nearly twice the volume of water is forced through the inlet than what would be produced by a similar size inlet with a sandy bottom and sides.
Coastal engineers gather information on tides and currents to investigate the tidal hydraulics of an inlet. These measurements will change over time as the inlet is altered by the accumulation of sand or construction activity. One of the most noteworthy studies of the Sebastian Inlet was conducted by the Coastal Engineering Laboratory at the University of Florida. They measured surface currents and tidal ranges in the inlet from July 1963-April 1964. Over this time period, their data reflected an average ocean tidal range at the inlet of 3.5 feet. From data obtained at the west end of the inlet, they calculated an average lagoon tidal range of 0.23 feet. The incoming tide through the inlet, call the flood, reached a peak velocity that averaged about 7.2 feet/sec. The current will then slow to a slack and reverse it's direction. The outgoing tide,or ebb, reached a higher peak velocity that averaged about 9.7 feet/sec.
Why is the tide in the lagoon so small compared to ocean tides? The Indian River Lagoon is 156 miles long and averages 3 feet in depth. In comparison the Inlet is like the tiny opening in an hourglass. The ratio of surface water in the lagoon compared to the flow area through the inlet is very small. The lagoon is just too large to fill up during a 12 hour tidal cycle and the inlet is too small for any significant amount of water to leave. As the surface water area of a lagoon system increases, the tidal range would approach zero.
Logging Requirements: Email your answers to the following question.
Stage 1: N 27 ° 51.576 W 080 ° 26.887 will bring you to a small fishing catwalk under the bridge.
1. Note the time of day and the direction, estimated in degrees, of the tidal flow through the inlet.
2. What was the most common item you observed passing through the inlet during your visit?
Stage 2: N 27 ° 51.622 W 080 °26.987 will bring you to an area call the swim cove. The size of the swimming area changes throughout the day as the tide ebbs and floods.
3. Walk the perimeter of the swimming area staying just at the water’s edge. Begin at the rip rap and continue north around the cove until you reach the other side of the rip rap. You do not need to enter the water. Use your GPS to measure the distance you traveled. Note this distance when you log your find for this cache so that others can see how it compares to their measurement. You might also want to upload a track log of your walk. All other logging requirements should be submitted by email; do not include them in your online logs.
4. Based on the direction of tidal flow you observed at stage 1, do you think the area of the swim cove is expanding or decreasing right now?
5. When data was collected by the University of Florida, the ebb flow was significantly faster than the incoming flood stage of the tidal cycle. Why do you think this difference existed? Use the following topographic diagram to explain your answer.
6. How might heavy rainfall on the mainland affect the ebb and flow rates through the inlet?
Please include any pictures you would like to share of the inlet when you log this cache as well as any interesting wildlife you observed.
The above information and photos were compiled from the following sources:
Historical timeline for Sebastian Inlet: http://research.fit.edu/zarillo/sebhist.htm
Historical pictures of Sebastian Inlet: http://www.sebastianinletdistrict.com/Inlet_History.html
Tidal hydraulic characteristics of the inlet: http://bcs.dep.state.fl.us/reports/sitidhyd.pdf
Florida State Parks: http://www.dep.state.fl.us/coastal/sites/gtm/quick_facts.htm
Congratulations to MollyMap for First To Log!