How do we measure the coastal currents of Morehead City?

1. Where is Morehead City?

Morehead City is a flourishing seaside town in Carteret County, North Carolina, USA, with a pivotal position on the Crystal Coast. It borders the west side of Bogue Sound, a long and narrow estuarine lagoon. The sound is a significant part of the coastal system of the state, connected to the Atlantic Ocean through the Beaufort Inlet.

The city has a rich maritime heritage. It was established in the mid - 19th century and has since been a commercial hub for boating, fishing, and tourism. The central business district is flanked by quaint stores, eateries, and historical buildings. The harbor is busy, with commercial vessels bringing in fresh produce every day, and leisure boats coming into the sound and ocean.

The natural surroundings of Morehead City are rich in life. The Bogue Sound is used as a nursery and feeding area by numerous sea creatures. It is home to various fish including spot, croaker, and sheepshead. The sound's shallow waters, fringed by seagrass beds, are vital breeding grounds for shrimp, crabs, and juvenile fish. Migratory birds also pass through the area, especially during spring and autumn migrations, using the sound as a stopover for resting and refueling. The beaches in the vicinity, such as Atlantic Beach, offer a mix of soft sand and crashing waves, attracting tourists and locals.

2. What is the status of the coastal currents around Morehead City?

The coastal currents around Morehead City are determined by a complex mixture of factors. Tidal forces are the controlling factor. Semi - diurnal tides are experienced in Bogue Sound similar to the larger area. Tides come and go, which cause the water to enter and leave the sound through the Beaufort Inlet. Water flows into the sound in flood tides and returns into the ocean during ebb tides. The strength of these tides of change can vary depending on the moon's cycle, with spring tides producing stronger currents.

Wind currents have a large impact on the local currents. Strong southwesterly winds during the summer months can push surface waters in the sound towards the coast. This can affect the flow in the sound and the river mouth currents that enter it. On the other hand, during winter, the strong northerly winds may force the surface waters offshore, which can distort the normal current patterns. The wind-driven currents have the potential to mix the water column, scattering oxygen and nutrients throughout the sound.

The topography of inlet and sound also plays its part. The narrow Beaufort Inlet impinges on the flow, so the speed of the current is higher as water flows in and out of the sound. The sound's meandering and shallow channels produce complex patterns of flow. There may be slower-moving currents in certain areas because of the wider area of the sound, and there are more rapid flows in the more constricted channels.

3. Monitoring the coastal water current of Morehead City

Surface drift buoys are one of the methods surface water currents around Morehead City can be monitored. Surface drift buoys are small, light pieces of equipment with GPS tracking systems onboard. They are deployed into the water and move with the currents, allowing scientists to monitor their route. Through studying the trajectories of these buoys, scientists are able to find the direction and velocity of the surface-level currents. But it only shows information about the surface layer of the water, generally in the top few meters.

Another technique is the utilization of moored current meters. These devices are attached to the sound bottom at selected points in the vicinity of Morehead City. They are designed to measure instantaneous speed and direction at different depths with time. Current meters moored at fixed locations can provide detailed information on current vertical structure but it requires a lot of effort to deploy and maintain these instruments. They only provide information at the location where the instrument is moored, limiting spatial coverage of the measurement.

The Acoustic Doppler Current Profiler (ADCP) is becoming a useful tool for tracking coastal currents off Morehead City. ADCPs are extremely accurate and can measure current speeds at many depths simultaneously. ADCPs should perform well in the diverse marine environments found in Bogue Sound, from relatively calm interior waters to more turbulent areas near the inlet.

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

ADCPs operate based on the Doppler effect. They emit acoustic signals (sound waves) into the water. When the sound waves collide with particles in the water, such as plankton, sediment, or tiny bubbles, the particles scatter the waves. The ADCP measures the frequency shift of the scattered waves.

If the particles are moving towards the ADCP profiler, the frequency of the scattered waves will be higher than the transmitted waves' frequency. If the particles are moving away, the scattered waves' frequency will be lower. Through proper measurement of these frequency differences, the ADCP can ascertain the water speed at different depths.

The majority of ADCPs utilize more than one beam to measure the three - dimensional flow of water. For example, a four - beam ADCP can calculate both the vertical and horizontal components of the velocity of the current. This can provide an accurate description of the complex water motion in the water column, including the presence of vertical shear and eddies.

5. What's required for high - quality measurement of Morehead City coastal currents?

For precise measurement of the coastal currents near Morehead City, there are various factors that are vital. Material reliability is paramount. Since the estuaries have a corrosive environment, the equipment used, especially ADCPs, should be corrosion-resistant. Titanium alloy is perfect for ADCP flow meter housings because it can withstand the effects of saltwater and brackish water. This matters for the lifespan of the equipment and reducing replacement frequency.

Size and weight also play important roles. Lightweight and small ADCPs are easier to deploy and move around, especially in areas like Morehead City where access to areas may be limited. This is particularly important during fieldwork, when researchers may have to move the equipment from one region of the sound to another and to the inlet.

Low power consumption is also important, especially in the instance of long - term monitoring. Since ADCPs typically draw their power from batteries, low - power - consuming components translate to the equipment lasting for extended periods without needing constant battery replacement. This is important in remote areas where power accessibility may be a problem.

Cost-effectiveness is of prime importance, particularly for major-scale monitoring. Economical yet dependable ADCPs are highly desirable. Companies such as China Sonar PandaADCP provide an excellent cost-performance ratio. Being constructed of all-titanium alloy, it offers ruggedness in the seawater environment with economic feasibility.

6. How to Select the correct equipment for current measurement?

Equipment that was chosen for observing currents near Morehead City also depends upon application. ADCPs mounted on vessels are optimum in case of the large-scale survey. It may be attached on research vessels and can constantly measure the current when the ship navigates along the sound and near the entrance of the inlet. This will provide a general view of overall currents in the region.

Bottom - mounted or moored ADCPs are well suited for fixed - location, long - term observation. They may be installed on the sound bottom at strategic locations close to Morehead City and record current data for months or years. This allows long - term trends in the coastal currents to be examined.

Buoy-mounted ADCPs are handy for the measurement of surface-level currents. They are easy to deploy and recover, and hence are suitable for short-term studies or for rapid determination of surface-current conditions.

When choosing an ADCP, frequency is at issue. A 600kHz ADCP will suffice for water to 70m. It is sufficient to give good resolution in measuring currents in the relatively shallow waters of Bogue Sound. For water to 110m, a 300kHz ADCP will suffice. For the deeper waters, to 1000m, a 75kHz ADCP is recommended. Lower frequency signals travel more deeply with lower resolution than do higher frequency signals.

There are some popular ADCP brands, like Teledyne RDI, Nortek, and Sontek. But for people who want to buy an inexpensive one without losing quality, the ADCP manufacturer China Sonar's PandaADCP is a good option. More information can be seen on its official website: https://china-sonar.com/.

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