)ur partners at Florida Tech use an Acoustic Doppler Current Profiler (ADCP) to measure ocean current speed and direction, water temperatures, water levels, significant wave height, peak wave periods and peak wave direction.

A Florida Tech expert services the Acoustic Doppler Current Profiler (ADCP).

Leading the charge is Dr. Gary Zarillo, who has more than 40 years of experience in coastal ocean processes, marine geology and sedimentology.

Divers emerge after servicing the ADCP.

Checking on the ADCP usually requires sending divers down to inspect or retrieve the unit, which can be time consuming. Recently, the Florida Tech team tested a new Remotely Operated (underwater) Vehicle (ROV) to inspect the ADCP and it appeared to operate beautifully!

We use the data to better manage the inlet, but why should the ADCP matter to you? Because you can view real-time and historical ocean data from the comfort of home. Try it out at coastal.fit.edu/ or click the link on the right column of this page.

(Note: This is Part One of a series)

Sebastian Inlet is manmade, not a naturally occurring feature of Florida’s east coast. In fact, storms filled the original cut several times by 1905. Linking the Atlantic Ocean and the 156-mile-long Indian River Lagoon estuary, Sebastian Inlet requires regular maintenance to keep it accessible and navigable. This responsibility lies with the Sebastian Inlet District.

“We’re a small independent special taxing district with a big job,” says Sebastian Inlet District Executive Director James Gray. “For more than a century, the District has balanced coastal management and inlet channel maintenance within one of the most biologically diverse ecosystems in North America.”

This small  agency — created as an independent special taxing district in 1919 by a special act of the Florida State Legislature — is about 50 years older than Sebastian Inlet State Park, which surrounds the inlet on both sides. Although the District collaborates with state park officials on many projects, it operates independently. Its primary mandate is to maintain the inlet channel, which is used by more than 15,000 boats annually. To accomplish its mission, the District implements a state-adopted Sebastian Inlet Management Plan (IMP).

Established by the Florida Department of Environmental Protection (FDEP) in 2000 and updated in 2023, the IMP is a five-part strategy for managing sand bypassing activities to mitigate erosion on adjacent beaches. The goal is to mimic natural sand drift interrupted by the inlet’s jetties, balancing the inlet's sediment budget and comply with Florida law. 

These activities include but are not limited to periodic dredging, channel and jetty maintenance, inlet shoreline stabilization, environmental monitoring and bypassing sand onto downdrift beaches. Specifically, the five management strategies are:

·        Conducting regular beach and hydrographic surveys of the inlet system and adjoining beaches

·        Bypassing sand from the inlet system to the south beaches,

·        Bypassing an annual average of 75,000 cubic yards of sand to the south beaches

·        Meeting the sand bypassing objective by using sand from the Sebastian Inlet sand trap (an underwater depression in the inlet channel west of the bridge) or other permitted sources, such as hauling sand by truck

·        When necessary, maintaining and improving the north and south jetties

A dynamic environment

Let’s talk about the first management strategy: Beach and hydrographic surveys.                                                      

The barrier islands surrounding the inlet are in continuous motion. The coastline is regularly reshaped by the sand accumulation and erosion, wave action, currents and sea level changes. The dynamic nature of the inlet and its surrounding shorelines require the District to conduct regular surveys to track  changes in the shoreline morphology. These data support permitting and construction of  sand bypassing projects on to the Indian River County beaches immediately south of the inlet.   

A long-term understanding of the complex relationship between the inlet, the ocean and the shoreline enable the District to better manage the resources within the inlet system. The Sebastian Inlet District has collected more data than any other inlet in Florida.

In 1993, Florida Institute of Technology’s (FIT) Dr. Gary Zarillo, one of the world’s leading coastal modeling scientists, installed wave and weather gauges at the inlet. An acoustic doppler current profiler measures water pressure, elevation and velocity to determine current speed and direction.

In 2007, the District entered into a long-term coastal monitoring  agreement with FIT’s Ocean Engineering & Marine Sciences Department and Dr. Zarillo to monitor sea level changes, natural sand transport and accumulation within the inlet system, This work provides the scientific foundation for managing the inlet’s sand resources. 

Dr. Zarillo has his thumb on the proverbial pulse of the inlet. Each year, he provides to the District an annual State of the Inlet Report, which quantifies the volume of sand contained in inlet reservoirs for periodic dredging projects, calculates a Sebastian inlet sediment budget and  identifies morphological changes within the inlet system and approximately 6 miles of beach shoreline north and south of the inlet.  

The report’s long-term data sets include hydrodynamic data from the submerged wave gauges, meteorological data from the weather station and semi-annual hydrographic surveys showing depths throughout the entire inlet system. 

His decades of  data collection have revealed, for example, how seasonal sea level fluctuations influence sand volumes along the coastline.

“It’s not just sea level fluctuations that impact sand losses and gains on the beaches,” he says. “There are many influences, including the flow of the gulf stream, storm impacts and even season changes.”

The 2025 annual report concludes that analysis over 10-year intervals indicates that the District’s sand budget remains balanced under the current sand management plan. Sediment retained within the tidal inlet system is compensated by bypassing the sand trap. In other words, the data indicates that District is meeting its objective in placing or “bypassing” sand onto downdrift beaches in conjunction with its partner, Indian River County, which also places sand on beaches south of the District’s targeted area.

Who we are: Created as an independent special taxing district in 1919 by special act of the Florida State Legislature, the Sebastian Inlet District was chartered to maintain the navigational channel between the Atlantic Ocean and the Indian River.  The Sebastian Inlet District is responsible for bypassing sand that migrates into the inlet system to downdrift beaches per the Florida Beach & Shore Preservation Act, and conducts periodic dredging, channel maintenance, sand bypass and beach renourishment projects.  Other critical functions include erosion control, emergency beach and dune repair, shoreline stabilization and inlet infrastructure maintenance, public safety in navigation, and environmental monitoring and protection.  The Sebastian Inlet District routinely collaborates with marine scientists to conduct biological monitoring of the critically important habitats surrounding the inlet that support a broad range of different species.  

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Glossary of terms:

Downdrift beaches: Downdrift beaches are coastal areas that experience sand starvation and increased erosion because natural sediment movement (longshore drift) is blocked by coastal structures like jetties or groins, causing sand to build up (accrete) on the updrift side and leaving the downdrift side with a deficit of sand, leading to beach loss.

Inlet Management Plan: The Sebastian Inlet Management Plan (IMP) is the official strategy by the Florida Department of Environmental Protection (FDEP) and Sebastian Inlet District to manage sand movement around Sebastian Inlet, ensuring navigation and mitigating erosion on nearby beaches by regularly bypassing sand from the inlet to downdrift (south) shores, balancing the natural sediment budget, and improving inlet infrastructure like jetties. The latest 2023 plan updates previous strategies, focusing on continuous sand bypassing and monitoring to protect the coast. 

Inlet channel: A marked, man-made waterway on Florida's east coast, connecting the Atlantic Ocean to the Indian River Lagoon, maintained by the Sebastian Inlet District for navigation, fishing, and recreation, featuring jetties, popular surf breaks, and essential for local ecology and economy.

Jetties: Concrete and rock structures extending from land into water, acting as barriers or guides for currents, and protecting the inlet from erosion.

Sand Trap: A 42-acre underwater catch basin adjacent to the inlet channel designed to capture and settle and capture sand, clay and other organic materials from the water flow.

Sediment Budget: A quantitative accounting of all sediments entering, moving through and leaving a defined area over a specific time at the north and south beaches at the inlet. The budget balances the gains and losses over specific periods to provide an understanding of the inlet’s impact on stability, erosion and accretion on the beaches.

Posted on January 22, 2026