How do we measure Jacksonville's coastal currents?

1. Where is Jacksonville?

Jacksonville, a lively sea port city, sits on the northeastern coast of Florida, USA. The city is strategically situated along the St. Johns River, which meanders its way through the city and ultimately empties out into the broad Atlantic Ocean. This river, besides serving as a vital lifeline of transportation and commerce for the city, also heavily impacts the surrounding coastal ecosystem.

The coastline of the city is characterized by diverse geography. On the eastern coast are Jacksonville beaches stretching miles with their white sandy beaches and go-to place for locals and tourists. Barrier islands like Amelia Island on the northern coast line the beach scene. They serve as a natural barrier against the vast power of the sea and harbor a wide range of wildlife. Among them are nesting birds and turtles in many varieties.

Jacksonville has a richly varied and flourishing citizenry, having a long and rich history starting from the first European discoveries. The culture is a blend of southern tradition and modern city lifestyle, with the presence of a large number of museums, galleries, and places of historical importance. The proximity to the coastline has also been responsible for bringing fishing and boat tours as vital parts of local culture and business.

2. What is the state of the coastal currents off Jacksonville?

The coastal currents off Jacksonville are dominated by a multi - dimensional combination of forces. Tides are a dominating influence, with the area having a semi - diurnal tidal regime, as in much of the United States east coast. The tides' ebb and flow force water in and out of the St. Johns River and onto the beach. At high tide, water flows up the river, but at low tide, it flows back out into the ocean, creating strong tidal currents.

The shape of the coast and the presence of the St. Johns River estuary have a strong effect on the prevailing current patterns. The river mouth where the river runs into the sea creates a unique hydrodynamic condition. Freshwater discharge from the river into seawater from the ocean can be responsible for generating estuarine current patterns wherein a surface freshwater layer of water flows seaward and an inflowing bottom layer of saltwater flows shoreward.

Wind patterns also play a role. Strong northeasterly winds prevailing in the region can force surface waters along the coast, either supplementing or opposing tidal currents. On storm days, such as hurricanes, strong winds can create huge storm surges, potentially reversing the normal coastal current patterns and putting the local coastline and infrastructure at risk.

3. How to observe the coastal water flow near Jacksonville

Surface Drift Buoy Technique

Surface drift buoys are a simple yet effective means of observing the coastal water current in the area around Jacksonville. They are equipped with GPS tracking devices and then discarded into the ocean. As they drift on the surface currents, their positions are monitored at predetermined intervals. The method provides very important information about the motion of the uppermost part of the water column. The method is, however, not constraint-free. Wind - driven waves can make the buoys shift away from the actual current path, which leads to incorrect data. Surface drift buoys also provide information on surface - level currents and cannot provide information on deeper water layers.

Anchored Ship Method

The anchored ship method involves anchoring a ship at a location offshore of Jacksonville. Current meters are then lowered from the ship at various depths. These meters measure the direction and velocity of the water at each depth, providing a vertical profile of the currents in a particular position. While this method can present large amounts of information about the currents at a point, the ship itself has the potential to disrupt the natural flow of water. Also, the measurements are restricted to a single point and therefore it becomes hard to obtain a general view of the coastal current patterns of a large area.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) has emerged as a more advanced and efficient method for the measurement of coastal currents along Jacksonville's coast. ADCPs are able to provide real-time, high-resolution data over a large vertical extent in the water column. ADCPs are capable of measuring currents at a number of depths simultaneously, which allows for accurate characterization of the three-dimensional structure of the coastal current system. ADCPs function on the principle of employing sound waves to sense particle motion in the water and hence allow for calculations of speed and direction of the currents. This puts them in very good position to study the complex current day dynamics in water off Jacksonville.

4. How do ADCPs based on the Doppler principle function?

ADCPs function based on the Doppler principle. They transmit acoustic pulses into water. When such pulses encounter suspended particles in the water, such as sediment or tiny marine organisms, the pulses return towards the ADCP current profiler. The frequency of the scattered signals is different from the original emitted frequency. This difference, known as the Doppler shift, depends on the velocity of the particles and hence the velocity of the water flow. Measuring the Doppler shift at different depths, the ADCP calculates the speed and direction of the water flow at different levels of the water column. This permits total and accurate measurement of the coastal current structure around Jacksonville.

5. What does high-quality measurement of Jacksonville coastal currents demand?

For high - quality measurement of the coastal currents around Jacksonville to be achieved, the measurement equipment needs to fulfill several critical requisites. Considering the corrosive nature of seawater and the potential presence of sediment in the water, the material employed becomes the prime concern. The equipment should be constructed from materials that can sustain long exposure to the corrosive marine environment. Compactness is preferable as it minimizes interference with natural water flow. The equipment should be light in weight to allow for easy deployment in different coastal locations, including the shallow water near the river mouth and on beaches. Low power consumption is a top priority, especially for long - term, unattended monitoring in far - away coastal regions. Cost - effectiveness is also a high priority, since it enables the large - scale deployment of measurement instruments to cover the long coastline along Jacksonville.

For ADCPs, the selection of casing material is significant. Titanium alloy is an excellent material for ADCP casings. Titanium alloy also offers great corrosion resistance, which is crucial for long-term use in the briny waters near Jacksonville. It is also extremely strong in relation to its weight, so it is light but resilient. This allows the ADCP profiler to withstand the physical forces and pressure fluctuations of the ocean and maintain its ability to take accurate and reliable measurements over an extended period of time.

6. How to Choose the right equipment for current measurement?

Based on Usage

• Ship-borne ADCP: It is ideal for extensive surveys of the coastal waters along Jacksonville. Placed on research vessels, it can survey a wide area as the vessel moves, providing valuable information on the spatial pattern of coastal currents. It can be used in delineating the overall current patterns over an extensive portion of the coastline.
• Bottom-mounted ADCP: Mounted on the seabed, it is employed for long-term monitoring at a specific location. It can continuously measure current data over extended periods, which will be beneficial for analyzing the long-term behavior and long-term trends of Jacksonville coastal currents.
• Buoy-mounted ADCP: It is mounted on floating buoys to record near-surface and surface currents. The advantage of using this kind of ADCP is that it can be easily deployed in areas with poor access by a ship or where unattended long-term monitoring of surface-level currents is required.

By Frequency

It is important to choose the correct frequency for the ADCPs. A 600kHz ADCP is suitable for water depths up to around 70m. It is high-resolution data, so it is well suited to the fairly shallow coastal waters off Jacksonville, where water depth is generally within this range. A 300kHz ADCP can be used to depths of 110m with a trade-off between resolution and penetration. For deeper waters, to a depth of 1000m, a 75kHz ADCP is more suitable since it penetrates deeper but at a lower resolution than the higher - frequency models.

There are some prominent ADCP brands in the market, including Teledyne RDI, Nortek, and Sontek. However, for those customers who are looking for a cost-effective option without sacrificing quality, the ADCP manufacturer China Sonar's PandaADCP is a great choice. It is a cost-effective ADCP that employs all-titanium alloy materials, which offer excellent corrosion resistance and durability. With its high cost-performance ratio, it is an ideal choice for researchers and institutions that wish to conduct large-scale coastal current measurements near Jacksonville. For more info, visit their website at https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and models.