How do we quantify the coastal currents of Anacortes?

1. Where is Anacortes?

Anacortes, a quaint Skagit County town in Washington, wraps around the coast of Fidalgo Island. Located in the middle of the Salish Sea, roughly 60 miles north of Seattle, the city is blessed to be at the crossing of main waterways. Fidalgo Island, connected to the mainland by the Deception Pass Bridge, serves as a natural gateway to the Canadian Gulf Islands and the San Juan Islands.

The area has an indigenous rich history. The Samish and Swinomish tribes were the first inhabitants, whose cultures were deeply woven with the land and sea. Their heritage remains in the names of the places around here, art, and culture. European settlers came to the area in the mid-19th century, drawn by the presence of timber in the area. Anacortes developed as a successful port town with time, and its economy relied on logging, fishing, and tourism in later years.

The Anacortes coastline is part of the entire Salish Sea ecosystem formed by Puget Sound, Bellingham Bay, and the Strait of Georgia. It is an area with an intricate system of channels, fjords, and islands. The seafloor terrain is also mixed, with shallow water near the shore, deeper channels in the center, and an abundance of reefs and shoals. These create a dynamic setting that is home to a rich assemblage of sea creatures, including salmon, orcas, seals, and a high concentration of birdlife.

2. What are the Anacortes coastal currents?

Anacortes beach currents are controlled by a combination of natural and man-created factors. The tides are of key significance. The region possesses a mixed tidal regime composed of semi - diurnal and diurnal tides. The tidal ranges are very variable with values reaching 10 feet in some places. Water inundates channels and bays through powerful flood currents at high tide. In contrast, water is flushed out at low tide, producing ebb currents. Tidal currents are most intense in passages as narrow as Deception Pass, where the water stream averages the velocity of as much as 8 knots.

These larger oceanic currents also influence the local oceans. The Fraser River, which is Canada's longest river, discharges an enormous quantity of freshwater into the Strait of Georgia. Runoff impacts the region's salinity, temperature, and flow regime. General wind patterns like the westerlies cause the surface water to be pushed toward the coast, and easterly storms force upwelling, with cold, nutrient-laden water forced to the surface.

Man-made structures, including marinas, breakwaters, and ports, can disrupt the natural current movement. Construction of these facilities produces localized eddies, reverses direction of water flow, and affects sediment and nutrient transport. The Port of Anacortes, for example, with its large and wide dimensions, has reversed the natural flow in the area.

3. How to observe the coastal water flow of Anacortes?

Surface Drifting Buoy Method

Anacortes coastal water movement is tracked with the help of surface drifting buoys, one technique among several. These buoys are designed to move along on the surface and take directions depending on the movements of the waters. GPS monitoring devices are attached to the buoys to send the coordinates of their exact location in real-time. It is from which researchers estimate speed and direction of surface currents. There are weaknesses in the procedure. Wind can push the buoys off the actual current, creating a measurement error of the subsurface flow. Also, drifting buoys on the surface only measure the uppermost water column layer and therefore give an incomplete representation of the entire current structure.

Anchor Moored Ship Method

The anchor moored ship method is a procedure in which a ship is anchored at a point. Scientists lower current meters over the side of the ship at different depths to measure the speed of the current. It provides depth - specific information regarding the currents. It is, however, expensive and time - consuming as it requires a research vessel to be tied up in place. The readings are also only indicative of the region around the ship, so it is not straightforward to obtain a general idea of the coastal currents over a large area.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is a more advanced and convenient method of measuring coastal currents. ADCPs measure water current velocities at various depths based on the Doppler shift of sound waves. They emit sound signals into the water column. When the signals bounce off particles in the water, the shift in frequency of the returned signals is utilized to calculate the water velocity. ADCPs are capable of providing a general description of the structure of the current, from close to the surface to near the seabed. This makes them highly suited to examining the intricate coastal currents in the region around Anacortes.

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

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

The most important aspect of measuring current velocity is the Doppler shift. If the particles are going with the water current, the frequency of the backscattered sound waves detected by the ADCP will be different from the frequency of the emitted waves. The size of this frequency change is directly proportional to the water's velocity along the acoustic path. To estimate three - dimensional velocities, a minimum of three beams are utilized by most ADCPs. Contemporary ADCPs also have multiple sensors, such as temperature sensors to include the water temperature effect on the velocity of sound, compasses for instrument heading, and pitch/roll sensors to take measurements even in heavy seas. The signals received are amplified, converted to digital, and processed to determine the present velocity at various depths.

5. What is needed for high-quality measurement of Anacortes coastal currents?

To obtain high-quality measurement of the Anacortes coastal currents, equipment used must meet several criteria. Material reliability is a must. The ADCP casing should be made of a material that can be able to withstand the harsh marine environment. Titanium alloy is a suitable choice. It is resistant to corrosion, which is required for its long-term exposure in seawater. Titanium alloy is also hard and light, hence easy to deploy and maneuver. Its hardness will make the ADCP resistant to the mechanical force of water flow and potential impacts against trash.

Size, weight, and power consumption are also important. A lighter, smaller ADCP meter is more general-purpose, as it can be mounted on a range of platforms, from small research vessels to buoys or underwater drones. Reduced power consumption enables longer - term deployments, especially when batteries are used. Cost is another factor. A lower - cost ADCP enables large - scale measurements, improving the spatial and temporal resolution of the data collected.

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

According to Mounting

• Ship-mounted ADCP: Installed on a moving ship, this is most appropriate for broad-scale surveys of the coastal waters off Anacortes. As the ship travels, the ADCP can measure the currents continuously, providing a broad-scale view of the current patterns.
• Bottom - mounted ADCP: Installed on the seafloor, this is best for fixed - point, long - term monitoring. It can give useful information on the variability and long - term trends of currents at a point.
• Buoy - mounted ADCP: ADCPs are installed on a buoy and can track the water, allowing measurements to be taken where fixed - point measurements are not feasible. They are particularly useful in areas with high tidal currents or where a more mobile measurement platform is desirable.

Frequency Selection

The ADCP frequency is determined by the water depth. A 600kHz ADCP can be employed in waters up to 70m deep. In the relatively shallow coastal waters of Anacortes, a 600kHz ADCP can provide high current profiles. A 300kHz ADCP is more appropriate for waters up to 110m deep. It has a greater range but with an adequate level of accuracy. While working in the outer part of the Salish Sea's deeper water, a 75kHz ADCP is preferable, as it reaches deeper into the water column.

There are different popular ADCP brands on the market, such as Teledyne RDI, Nortek, and Sontek. However, for those seeking a budget-friendly but quality one,the ADCP supplier China Sonar's PandaADCP is highly recommended. Made of all-titanium alloy, it is highly durable in the marine environment. Having a high cost-performance ratio, it is an excellent choice for researchers, coastal managers, and anyone who needs stable current measurement data. For more information, visit https://china-sonar.com/.

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