How do we measure the coastal currents of Seattle?

1. Where is Seattle?

Seattle, the metropolitan capital of the Pacific Northwest region of the United States, holds a strategic position on the shores of Puget Sound. It lies between Puget Sound and Lake Washington, and the geography of Seattle is unique because it is a seaport city. Seattle lies some 100 miles south of the American-Canadian border and is a leading economic, cultural, and technological center.

The area was originally inhabited by the Duwamish tribe. Their rich cultural heritage, with roots in water and earth, remains intact in local place names, art, and tradition. European settlers arrived in the mid-19th century, attracted by the natural resources of the region, including timber, salmon, and proximity to waterways. Seattle ultimately developed into a thriving port city, with its history being linked closely with the logging, fishing, and shipping industries. Today, it is known for its cosmopolitan technology scene, coffee shops, and iconic landmarks such as the Space Needle.

The oceans off Seattle are part of the Puget Sound ecosystem. Puget Sound itself is a multi-dimensional estuary, a collection of bays, channels, and inlets. The underwater topography surrounding Seattle varies from shallow sandy beaches close to shore to deeper channels and troughs off shore. The presence of rocky reefs and subterranean reefs is a unique setting that offers a source of livelihood to a wide array of marine fauna and flora. From sea lions and seals to seabirds and crab, as well as salmon, the area harbors an incredible array of biodiversity.

2. How are the coastal currents around Seattle?

The nearshore currents off Seattle are driven by a complex mix of natural and man - induced conditions. Tides play a role. Puget Sound has a mixed tidal regime. Semi - diurnal and diurnal tides occur, with tidal ranges of up to 15 feet in certain locations. During high tide, water flows into the bays and inlets off Seattle, creating intense flood currents. As the tide recedes, ebb currents force water back into the main body of the sound. The tidal currents are more powerful in narrow channels, such as the Hiram M. Chittenden Locks, connecting Lake Washington and Puget Sound.

The larger ocean currents also influence the waters locally. Movement of water through the Strait of Juan de Fuca, which connects Puget Sound to the Pacific Ocean, controls temperature, salinity, and Seattle coastal water currents. Wind patterns also exert an influence. Westerly winds push the surface waters onshore, while strong easterly winds result in upwelling. Upwelling phenomena bring cold, nutrient - rich water to the surface, promoting the growth of phytoplankton and supporting the entire marine food chain.

Human activities have also disrupted the natural current circulation. Construction along the Seattle waterfront, such as marinas, docks, and seawalls, has distorted the normal circulation patterns. These man - made structures can induce local eddies, deflect water movement direction, and affect sediment and nutrient distribution. In addition, the presence of wide shipping lanes and ports in the area may influence the governing regime because the movement of ships may produce wake and alter local water flow.

3. How to measure the Seattle coastal water flow?

Surface Drifting Buoy Method

One way to measure the Seattle coastal water flow is through the use of surface drifting buoys. These buoys float on the water's surface and follow the currents. The buoys carry GPS tracking devices that provide real-time location information. Scientists determine the direction and velocity of the surface currents based on the information obtained. There is a limitation with this method. Wind will push the buoys off the current, making it impossible to have the actual subsurface flow. Additionally, surface drifting buoys provide information only about the surface layer of the water column, which only offers a limited view of the entire current structure.

Anchor Moored Ship Method

Anchor moored ship method involves the anchoring of a ship in a specified position. Scientists take current meters out over the ship's bow in different depths in order to measure the velocity of the current. It provides depth-specific information regarding the currents. But it is slow and expensive since a research vessel has to remain in one spot. The readings are also representative only of the vicinity of the ship, so it is difficult to have an overall idea of the coastal currents in a vast area.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is now a more advanced and easier-to-use coastal current measuring instrument. ADCPs determine water current velocities at various depths using the Doppler shift of sound waves. ADCPs emit the sound signals into the water column. When the sound signals bounce off particles in the water, the frequency shift of the returned sound signals is computed to achieve the water velocity. ADCPs are capable of giving a detailed picture of the present structure from the surface down to almost at the seabed. Therefore, they are well suited for observing the complicated coastal currents around Seattle.

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

ADCPs rely on the Doppler effect. They utilize piezoelectric transducers to transmit sound into the water. When the sound waves bounce off particles such as plankton, sediment, or bubbles in the water, they bounce some of the sound energy back towards the ADCP flow meter. The time that it takes the sound waves to travel to the particles and return provides an estimate of how far away the particles are.

The Doppler shift is the key to measuring current velocity. When the particles are traveling with the water current, the frequency of the scattered sound waves from the ADCP will not be the same as the frequency of the waves emitted. The magnitude of this frequency shift is proportional to the speed of the water along the acoustic path. To measure three - dimensional velocities, most ADCPs use a minimum of three beams. Recent ADCPs also include other sensors, including temperature sensors to account for the effect of water temperature on the speed of sound, compasses to determine the instrument heading, and pitch/roll sensors to make measurements even in rough seas. The received signals are amplified, digitized, and processed to calculate the current velocity at different depths.

5. What are the demands for high-quality measurement of Seattle coastal currents?

Equipment to be used for high-quality measurement of coastal currents in Seattle must fulfill some demands. Material reliability is most important. The casing of the ADCP must be constructed of material capable of being applied in a harsh marine environment. Titanium alloy would be an excellent choice. It is also very resistant to corrosion, a condition necessary for long-term use in seawater. Titanium alloy is also very light and strong, hence it will be lighter to deploy and maneuver. Its strength ensures that the ADCP will be able to withstand mechanical water flow stress and incidental impacts from trash.

Size, weight, and power consumption are important too. Lighter and smaller ADCP meter is more versatile since it can be mounted on a variety of platforms, from small research vessels to buoys or underwater vehicles. Lower power consumption translates to longer - term deployments, especially with battery power. Cost is important too. An inexpensive ADCP enables large - scale measurements, thus the spatial and temporal resolution of the data acquired becomes greater.

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

Types Based on Mounting

• Ship-mounted ADCP: Installed on a traveling ship, this type is ideal for large-scale surveys of Seattle coastal waters. As the ship travels, the ADCP can continuously measure the currents, providing a broad-scale picture of the current patterns.
• Bottom-mounted ADCP: Mounted on the bottom of the sea, it is ideally suited for fixed - point, long - term observation. It can provide valuable insight into the long - term trends and variability of the currents at a specific point.
• Buoy-mounted ADCP: Suspended from a buoy, these ADCPs can travel along with water, and thereby permit measurements when fixed-point measurements are not practicable. They are particularly useful in areas with high tidal current or where there is a requirement for a more movable measurement platform.

Frequency Selection

An ADCP's frequency varies based on the water depth. A 600kHz ADCP is suitable for water depths up to 70m. In the relatively shallow coastal waters off Seattle, a 600kHz ADCP can provide accurate current profiles. For water depths up to 110m, a 300kHz ADCP is better. It has a greater range but still a good level of accuracy. For the intent of treating shallow waters on the periphery or in the margin of the central Puget Sound, a 75kHz ADCP would be the ideal choice since it would be capable of penetrating deeper inside the water column.

Certain brands of ADCP are hugely popular in the market, such as the likes of Teledyne RDI, Nortek, and Sontek. To those who seek an affordable but quality-based alternative, then the ADCP manufacturer China Sonar's PandaADCP would definitely be highly recommended. Made of all-titanium alloy, it delivers better endurance in the seawater environment. Enjoying a better cost-performance rate, it is an ideal choice for scientists, coastal authorities, and whoever needs reliable current measuring data. To learn more about it, visit https://china-sonar.com/.

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