How do we measure Edmonds' coastal currents?

1. Where is Edmonds?

Edmonds is a charming Snohomish County city in the state of Washington, located along Puget Sound, approximately 18 miles north of Seattle. The small yet vibrant city is renowned for its beautiful beaches, water front parks, and historical marine heritage. The soundside position of the city provides ease of access to a diverse array of marine habitats, and as such, it is a top destination for boat tours, fishing, and wildlife watching.

The area was initially occupied by the Snohomish tribe, and their existence was heavily rooted in the water and land. Their legacy is seen in local names, art, and tradition. The European settlers arrived in the mid - 19th century, attracted by the area's natural beauty and economic prospects. Edmonds was shaped by the logging and fishing industries, and the port as a prime trading center.

The ocean waters off the coast of Edmonds are part of the broader ecosystem of the Puget Sound. The sound itself is a complex network of channels, inlets, and bays with diverse underwater geography. Rocky and sandy shallows near the shore yield to deeper basins and channels a considerable distance from the shore. The presence of numerous reefs and islands in the sound creates a dynamic environment that accommodates a long list of sea life, including salmon, herring, seals, sea lions, and various bird species.

2. What is the status of the coastal currents near Edmonds?

The coastal currents near Edmonds are shaped by a combination of natural and human - caused influences. Tides are an important component. The Puget Sound possesses a mixed tidal regime with semi - diurnal (two highs and two lows each day) and diurnal (one high and one low per day) features. The range of tides is quite diverse and can extend up to 15 feet in places. At high tide, water inundates the Edmonds' area bays and channels, filling high flood currents. Conversely, when tides are low, water tends to flow outward, forming ebb currents. The tidal currents are most effective in the constrained channels and across the islands of the sound.

The greater ocean currents in the region also impact the regional waters. Water flow through the Strait of Juan de Fuca, which connects the Puget Sound to the Pacific Ocean, affects the temperature, salinity, and current in the region. Wind regimes, such as the westerlies, can force surface waters onshore, whereas strong easterly winds can cause upwelling, pushing cold, nutrient - filled water to the surface.

Human-made constructions such as ports, marinas, and breakwaters may disrupt the natural flow of currents. Edmonds Marina, being a complex one, has disrupted the natural circulation pattern surrounding the surrounding area. The construction of the structures will cause local eddies, change the direction of the water flow, and affect the sediment and nutrient distribution.

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

Surface Drifting Buoy Technique

Another method of observing the movement of coastal water along Edmonds is through the use of surface drifting buoys. The buoys are deployed on the surface of water and drift with the currents. The buoys are equipped with GPS tracking devices that are implanted in them, and they transmit real-time location data. Scientists use this data to compute the velocity and direction of surface currents. This technique is not without flaws. Wind can cause the buoys to stray from the actual current, providing a false reading of the subsurface flow. In addition, surface drifting buoys report only about the uppermost part of the water column, providing a limited picture of the overall current structure.

Anchor Moored Ship Method

The anchor moored ship method is to place a ship at a single location. Scientists lower current meters off the side of the vessel at different depths to measure the speed of the current. The method provides depth - specific information on the currents. It is, however, time - consuming and expensive since it entails a research vessel that is moored in place. These measurements are also confined to the neighborhood of the vessel alone and would be struggling hard to give an overview of coastal currents over large geographical areas.

Acoustic Doppler Current Profiler (ADCP) Method

Acoustic Doppler Current Profiler (ADCP) is presently a better and more laid-back method in measurement of coastal currents. The principle of sound Doppler is utilized by the ADCPs for measurement of velocities of water currents over various depths. They emit sound waves into the water column. When the sound signals are reflected off particles in the water, the change in frequency of the backscattered signals is used to calculate water velocity. ADCPs are capable of providing a comprehensive description of the current profile, from near the surface down to near the seabed. ADCPs are ideally suited for studying complicated coastal currents off Edmonds.

4. How does an ADCP operating on the Doppler principle work?

ADCPs operate based on the Doppler principle. They employ piezoelectric transducers, which emit sound waves into the water. As the sound waves interact with particles such as plankton, sediment, or bubbles in the water, a part of the sound energy bounces back to the ADCP flow meter. The time the sound waves take to travel to the particles and come back provides an estimate of the distance to the particles.

The principle behind the measurement of current speed is the Doppler shift. If the particles are transported by the water flow, the returned sound wave frequencies measured by the ADCP would be other than the emitted ones. The extent of this shift in frequency increases with the flow speed of water along the acoustical pathway. To measure three-dimensional velocities, most ADCPs will have at least three beams. ADCPs today also carry sensors like temperature sensors to correct for water temperature's influence on sound velocity, compasses to inform the orientation of the instrument, and pitch/roll sensors to deliver accurate measurement even in rough seas. Incoming signals are amplified, digitized, and processed to calculate the current velocity at different depths.

5. What are the requirements for high-quality measurement of Edmonds coastal currents?

High-quality measurement of Edmonds' coastal currents would require that the equipment used meets certain specifications. The ability of the material to be reliable is very important. The casing of the ADCP current meter should be made of a material that can stand the aggressive marine environment. Titanium alloy would be very appropriate. It has excellent corrosion resistance, which is critical for long-term use in seawater. Titanium alloy is also strong and light, so it is more suitable to handle and deploy. Its strength gives the ADCP the ability to resist mechanical water motion and potential impact from trash.

Weight, size, and power usage are also important. A smaller, lighter ADCP is more generally applicable because it can be utilized on a variety of platforms, from small research vessels to underwater robots or floats. Reduced power usage implies long - term deployment, especially in cases where power comes from a battery. A lower cost also helps. Less expensive ADCPs make large - scale measurements practical, increasing spatial and temporal resolution of the obtained data.

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

By Mounting

• Ship-mounted ADCP: On a floating vessel, this equipment would be most effective in large - scale surveys of Edmonds coastal waters. With the vessel travelling along, the ADCP would continuously measure the currents, presenting a general - scale view of the current pattern.
• Bottom-mounted ADCP: Installed on the sea floor, this type is best suited for fixed-point, long-term observation. It can provide valuable information on the long-term trends and variability of currents at a given point.
• Buoy-mounted ADCP: Mounted on a buoy, ADCPs can follow the water with it, making measurements in situations where fixed - point measurements would be impractical. They are particularly handy where there are strong tidal currents or where a more mobile measurement vehicle is required.

Frequency Selection

The depth of the water determines the ADCP's frequency. A 600kHz ADCP can be utilized for water depth up to a maximum of 70m. For the relatively shallow coastal waters near Edmonds, a 600kHz ADCP can be utilized for satisfactory current profiles. For water up to 110m, a 300kHz ADCP would be more suitable. It gives a longer range but still has a very high level of accuracy. When operating in the deeper waters of the central Puget Sound, a 75kHz ADCP is the preference since it will reach deeper into the water column.

A few of the most well - known ADCP brands currently available include Teledyne RDI, Nortek, and Sontek. For those, however, who are looking for a cost - effective but high - quality ADCP, the ADCP manufacturer China Sonar's PandaADCP is highly recommended. Made of all-titanium alloy, it offers better resistance to the sea environment. Long-lasting at a very affordable cost, it is the ideal choice for researchers, coastal managers, and anyone needing precise current measurement data. To find out more, visit https://china-sonar.com/.

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