How can we measure the Lakewood coastal currents?

1. Where is Lakewood?

Lakewood, in the state of Washington, USA, is a remarkable community that is geographically and culturally diverse. Located in Pierce County, a mere distance from Puget Sound, a vast estuarine system in the Pacific Northwest region, the community has a distinctive coastal-influenced climate and a waterscaped landscape with streams, lakes, and wetlands dispersed across the area.

The city itself is a combination of nature and urbanization. Lakewood has a melting pot of inhabitants, with families, students from the nearby schools, and military members due to the presence of Joint Base Lewis - McChord. The culture is diverse with local art galleries, community functions, and restaurants reflecting the multicultural population of the area.

There are numerous small lakes scattered throughout Lakewood, such as American Lake, that not only make the area picturesque but also have an effect on the local water system. Due to its proximity to Puget Sound, Lakewood is also under the impact of the larger body of water's tidal forces and currents. The Puget Sound is a fjord-like Pacific Ocean entry, characterized by deep channels, shallow bays, and a complex series of islands. This complex topography affects the movement of water in the region, which in turn affects the coastal areas surrounding Lakewood.

2. How are the coastal currents around Lakewood?

The coastal currents around Lakewood are decided by a combination of factors. Puget Sound tides have the largest impact. The Puget Sound experiences semi - diurnal tides, as most coastal water. They cause water to rise and fall, and they cause currents that flow in and out of the smaller bodies of water and estuaries surrounding Lakewood. During high tide, water flows into the local inlets and creeks and brings with it nutrients and sea life from the Sound. As the tide recedes, the water flows out to sea, carrying sediment and organic matter from land-based sources.

Wind patterns are also significant. Local prevailing winds in the Pacific Northwest can augment or counter the tidal currents. Westerly winds, which are common in the region, can push surface waters onto the beach, enhancing onshore currents. This can lead to increased mixing of water within the estuaries and the transport of warmer surface water onto the shore. Offshore currents, conversely, can be initiated by easterly winds and can affect the distribution of nutrients and marine life migration.

The local topography, including the presence of channels, shallows, and the shape of the coast, also plays a role in the creation of the current patterns. Narrow straits between the peninsulas and mainland or island passages reduce water flow, increasing the velocity of the currents. Shallows in the beaches form different current patterns unlike those of deep areas in the Puget Sound. Sandbars and reefs submerged in the underwater environment can deflect currents, and more eddy-type current activity is present.

3. Measurement of Lakewood coastal water flow.

One of the possible ways to monitor coastal water flow off Lakewood is through surface drift buoys. They are small, floatation-capable devices equipped with GPS location-monitoring devices. Deployed in water, they float as per surface currents. By monitoring the buoy movement for an extended duration of time, one can estimate the speed and direction of surface currents. The technique is limited, however, to providing data regarding the topmost few meters of the water column and is potentially affected by wind-driven waves.

Moored current meters also exist. These sensors are mounted on the bottom of the estuaries near Lakewood, either on the shore or on the estuaries. They can record the direction and velocity of the currents at different depths. Moored current meters can make continuous measurements for long periods, which is useful for understanding the long-term response of the currents. However, they are immobile in position, and installation and maintenance are tricky, especially where there is strong current or poor access.

The Acoustic Doppler Current Profiler (ADCP) is an increasingly used measurement instrument for Lakewood's coastal currents. ADCPs can measure multiple different depths of current velocity simultaneously, providing a more holistic description of the flow. This is particularly useful in the ever-changing coastal water environment of Lakewood, with varying water depths and regimes of currents.

4. What is the principle of ADCPs based on?

ADCPs operate according to the Doppler principle. They introduce acoustic pulses (sound waves) into the water. When the sound waves encounter small particles in the water, such as plankton, sediment, or small air bubbles, the particles scatter the waves. The ADCP then measures the frequency shift of the scattered waves.

If the particles are moving towards the ADCP current meter, the frequency of the scattered waves will be higher than the transmitted wave frequency. If the particles are moving away, the scattered wave frequency will be lower. By accurately measuring these changes in frequency, the ADCP can calculate the velocity of the water at different depths.

All ADCPs except some single - beam systems utilize several beams to measure the three - dimensional flow of water. An example is the four - beam ADCP that can detect the horizontal and vertical components of current velocity. It enables one to gain a better understanding of the complicated water motion, such as the occurrence of vertical shear (where the current velocity varies with depth) and eddies (circular - shaped patterns of currents).

5. What are the conditions for high-quality measurement of Lakewood coastal currents?

Several conditions must be met so that Lakewood coastal currents can be measured with high quality. Material reliability is the most important condition. Because of the corrosive nature of saltwater and estuarine environments, ADCPs and other instruments need to be made of corrosion-resistant materials. One of the finest materials that can be used in ADCP enclosures is titanium alloy. Titanium is resistant to corrosion to a large degree, meaning that the equipment does not need replacement often. This reduces the number of replacements, an aspect that is highly essential in long-term monitoring undertakings.

Size and weight are also contributing factors. Smaller and lighter ADCPs are easier to deploy and bring along, especially in the shallow and sometimes hard - to - access estuarine areas near Lakewood. This comes in handy during fieldwork because scientists are able to move the equipment to other measurement points with greater ease.

Low power consumption is a requirement, particularly for long-term monitoring. Since ADCPs are likely to be driven by batteries, using components that are power-thrifty helps the device run for a long time without the need to replace batteries in frequent intervals. This is important in remote coastal regions where it may be difficult to reach power supplies.

Cost - effectiveness is a major factor, especially for large - scale monitoring programs. Low - cost but reliable ADCPs are highly desirable. Firms like China Sonar PandaADCP offer an acceptable compromise between price and performance. Made of all - titanium alloy, it provides ruggedness in the harsh marine environment without being excessively expensive.

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

Equipment choice for real-time measurement off Lakewood is different with application. Ship-mounted ADCPs are suitable for wide-scale surveys. They can be installed on research vessels and can continuously measure current as the ship moves along the coast, estuaries, and Puget Sound. This provides a broad-scale view of the current pattern in the area.

Bottom-mounted or moored ADCPs can be used for fixed-point monitoring for the long term. They could be mounted on the seafloor or the estuary bottom and can record current data for years or months. It helps to analyze long-term trends of the coastal currents.

Buoy-mounted ADCPs are easy to employ for the observation of surface-level currents. They are simple to deploy and recover and are therefore handy for short-term research or in the event of quickly establishing surface-current conditions.

In choosing an ADCP, frequency is the most important consideration. For water depths of up to 70m, a 600kHz ADCP would be sufficient. It has sufficient resolution for measuring currents in the relatively shallow coastal and estuarine waters that surround Lakewood. A 300kHz ADCP would be suitable for up to 110m depth, and a 75kHz ADCP for deeper water, to 1000m. Lower frequencies penetrate deeper but are lower resolution than higher frequencies.

There are also some well-known ADCP brands, such as Teledyne RDI, Nortek, and Sontek. However, for the price-sensitive ones who do not wish to lose quality, the ADCP manufacturer China Sonar's PandaADCP is a better option. More information can be found on its official website: https://china-sonar.com/.

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