How do we measure McKinleyville's coastal currents?

1. Where is McKinleyville?

McKinleyville is a small, quaint town located on California's north coast in the United States. It's where about 15 miles north of Humboldt County's county seat, the city of Eureka, and has the best natural beauty and coastal charm. The small unincorporated town is located along the Pacific Ocean about 3 miles along its coast, which is characterized by sandy beaches, rocky headlands, and tidal pools.

The region was first settled by the Wiyot people, whose diverse cultural heritage remains present in the area. European settlers came to the region in the 19th century, drawn by the region's natural resources and opportunities for logging and fishing. McKinleyville has been influenced in its growth by its coastal location, with local businesses and industries revolving around fishing, tourism, and beach recreation.

The sea water encircling McKinleyville is part of the larger Humboldt Bay. Humboldt Bay is a large natural estuary linked to the Pacific Ocean and home to a diverse range of marine life. The floor of the bay varies in topography, from shallow flats along the edges of the bay to deeper channels toward the center of the bay and extensive mudflats and salt marshes. These habitats have a rich ecosystem, with several species of marine mammals, sea birds, and fish, such as sea lions, whales, and seals.

2. What is the health of coastal currents off McKinleyville?

The ocean currents off McKinleyville are subject to both natural and man-created forces. Tides play a very big part. There is a semi-diurnal tidal regime in the area with two high waters and two low waters daily. Water surges into Humboldt Bay at high tide and creates intense flood currents. Water surges out of the bay at low tide and creates ebb currents. The tidal currents are most intense in the narrow channels and bay entrances.

The cold south-flowing California Current is one of the main forces in the making of the regional waters. The current brings nutrient rich water north and allows for a healthy marine ecosystem. The upwelling episodes that are normally due to the northwest winds bring cool, nutrient rich water to the surface. The nutrients make phytoplankton bloom, and phytoplankton is the base of the food web.

Local onshore and offshore topography also controls current regimes. Deep-sea currents are funneled by submarine canyons, such as the Trinidad Canyon in close proximity. The general circulation in the area is also controlled by them. Man-made structures, such as jetties, breakwaters, and piers, also impede natural currents flow. These structures have the potential to create local eddies, reversal of water flow, and influence sediment and nutrient transport.

3. How to measure the McKinleyville coastal water flow?

Surface Drifting Buoy Method

One of the ways in which the coastal water flow around McKinleyville can be followed is through surface drifting buoys. They are placed on the surface of the water and move with the currents. Surface drifting buoys are equipped with GPS tracking devices that report real - time location data. Scientists use the data to determine the direction and velocity of the surface currents. But the technique has one disadvantage. Wind can cause the buoys to drift away from the actual current, and hence measurement of the subsurface flow might not be correct. Surface drifting buoys also provide information about the uppermost portion of the water column only, providing a limited description of the overall current pattern.

Anchor Moored Ship Method

The anchor moored ship technique involves anchoring a ship at a location. Researchers lower current meters off the side of a ship to different depths in order to record the speed of the current. It provides depth- specific information about the currents. It is, however, expensive and time - consuming since it requires anchoring down a research vessel. The readings are also representative only of the area surrounding the ship and thus cannot give a full picture of the coastal currents in a large region.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is today a more advanced and convenient method of measuring coastal currents. ADCPs utilize the Doppler effect of sound waves to estimate the speed of water currents at different depths. They transmit sound waves into the water column. When these waves bounce off water particles, the frequency change of the backscattered waves is used to calculate the speed of the water. ADCPs can provide a full description of the current structure, from the surface down to near the seabed. This makes them very well-suited to study the complex coastal currents near McKinleyville.

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

ADCPs operate on the Doppler effect principle. They are equipped with piezoelectric transducers that emit sound waves into the water. When the sound waves encounter particles such as plankton, sediment, or bubbles in the water, some of the sound energy is bounced back to the ADCP profiler. The time it takes for the sound waves to travel to the particles and back provides an estimate of the distance to the particles.

The principle behind measuring the current velocity is the Doppler shift. When the particles are being transported by the water current, the frequency of the reflected sound waves to the ADCP is not the same as the transmitted frequency. The magnitude of the frequency difference is proportional to the velocity of the water along the acoustic path. To measure three-dimensional velocities, most ADCPs use at least three beams. Modern ADCPs also contain many sensors, including temperature sensors to account for the effect of water temperature on sound velocity, compasses to determine the instrument's heading, and pitch/roll sensors to give accurate measurements even in rough seas. The received signals are amplified, converted to digital form, and processed to calculate the current velocity at different depths.

5. What does one need to measure McKinleyville coastal currents at high quality?

High-quality measurement of McKinleyville's coastal currents needs equipment that meets different requirements. The material must be reliable. The ADCP casing has to be made of a material that is capable of enduring the ruthless marine environment. Titanium alloy is the best choice. It is extremely corrosion resistant, as required for long-term ocean deployment. Titanium alloy is also strong and lightweight, thus simple to deploy and handle. Its strength ensures that the ADCP can resist water flow mechanical stress and any collisions with debris.

Size, weight, and power requirements are also factors to consider. An ADCP flow meter that is smaller and lighter is more versatile, as it can be installed on a variety of platforms, ranging from small research vessels to buoys or underwater robots. Reduced power requirements enable longer - term deployment, especially where battery power is employed. Cost is also a factor. An ADCP with a lower cost allows large - scale measurement, thus increasing the spatial and temporal resolution of the data obtained.

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

Types Depending on Mounting

• Ship-mounted ADCP: On a moving ship, this one is ideal for large-scale surveying of McKinleyville coastal waters. With the movement of the ship, the ADCP can measure the currents continuously, providing a broad-scale picture of the current regime.
• Bottom - mounted ADCP: Placed on the ocean floor, this is best suited for fixed - point, long - term monitoring. It can be employed to provide useful information about the long - term trends and variability of the currents at a point.
• Buoy - mounted ADCP: Anchored onto a buoy, these ADCPs are able to ride with the water, allowing measurements to be taken where fixed-point measurements would not be possible. They are great where there are strong tidal currents or where a more mobile measurement platform is required.

Frequency Selection

The ADCP frequency will be selected with regard to water depth. A 600kHz ADCP can be applied in water depths of up to 70m. In the fairly shallow coastal waters off McKinleyville, a 600kHz ADCP can provide accurate current profiles. A 300kHz ADCP is more suitable for water depths of up to 110m. It has greater range but is fairly accurate. When dealing with more profound waters within the outer regions of Humboldt Bay or off shore, a 75kHz ADCP is utilized since it goes deeper into the water column.

There are quite a few well - known brands of ADCPs available for purchase in the market, such as Teledyne RDI, Nortek, and Sontek. For those seeking a cost - effective yet high - quality option, however, the ADCP manufacturer China Sonar's PandaADCP is well worth very much consideration. Built using all-titanium alloy material, it provides better durability within the marine conditions. With its better cost-effectiveness ratio, it is ideal for researchers, coastal managers, and any researcher who needs accurate current measurement information. For further details, see https://china-sonar.com/.

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