How do we measure the Bellingham coastal currents?

1. Where is Bellingham?

Bellingham is a thriving community in northwestern Washington state and borders the shores of Bellingham Bay, an inlet of the Salish Sea. Located about 90 miles northeast of Seattle and 25 miles south of Canada, it's a major cultural and economic hub in the region. The town land is a blend of coastal plain and their surrounds foothills, which offer an amazing view of the sea as well as land to residents as well as temporary inhabitants.

There is an abundance of native heritage in the site. The area was first populated by the Nooksack and Lummi folk, whose lives were built by the land, rivers, as well as seas. Today, their legacy continues to be felt in various types of cultural practice, art, and historical landmarks. The area was settled by European settlers during the mid-19th century, enticed by the area's natural resources, primarily wood. Bellingham became a thriving port city over time, with its economy revolving around logging, fishing, and foreign trade.

Bellingham Bay is framed by the greater Salish Sea environment, to which Puget Sound and Strait of Georgia also belong. Seafloor topography within the bay ranges from shallow nearshore water to deeper mid-channel water, as well as extensive islands and reefs. Dynamism and complexity produced by these structures provide support for an assortment of marine wildlife, including salmon, herring, seals, sea lions, and numerous birds.

2. What are the coastal currents around Bellingham like?

The coastal currents around Bellingham are influenced by natural and man - made factors. Tides play a significant role. The region has a mixed tidal regime with both semi - diurnal (two highs and two lows daily) and diurnal (one high and one low daily) components. Tidal ranges are large, as much as 10 feet or more in some places. Water enters the bay during high tides and generates powerful flood currents. Water exits during low tides and generates ebb currents. The tidal currents are particularly powerful in the tight channels and off the many islands of the bay.

The larger oceanic currents of the Salish Sea also affect the local waters. The Fraser River, the longest river in Canada, discharges a large volume of freshwater into the Strait of Georgia. The outflow influences the temperature, salinity, and flow characteristics in the area. Furthermore, the regional wind patterns have the tendency to strongly influence the coastal currents. Westerly winds prevailing can force surface waters ashore, whereas easterly winds can produce upwelling, forcing cold, nutrient - laden water to the surface.

Man-made infrastructure such as ports, marinas, and breakwaters can misorient the natural flow of currents. During their construction, local eddies are formed, water flow is reversed, and sediment and nutrient distribution are affected. For instance, the Bellingham port with its extensive infrastructure has distorted the original patterns of circulation within the bay.

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

Surface Drifting Buoy Technique

Another way of monitoring coastal water currents near Bellingham is through the use of surface drifting buoys. Surface drifting buoys are utilized to monitor the direction and velocity of surface currents by floating on the surface of the waters and drifting with the current. Using GPS tracking units, buoys transmit real-time location data. Scientists analyze the data to determine the direction and velocity of the surface currents. However, this method has its limitations. Wind can cause the buoys to drift away from the actual current, giving false measurements of the subsurface flow. Moreover, surface drifting buoys are only reporting on the very surface of the water column, and only for a brief moment of the entire current structure.

Anchor Moored Ship Method

Anchor moored ship method involves mooring a ship at a fixed point. Scientists drop current meters down the side of a ship at different depths to measure the speed of the current. This method provides depth - specific information on the currents. However, it is expensive and time - consuming as it requires anchoring a research ship in position. The readings are also representative of only the area near the ship, so a full picture of coastal currents in an expansive area cannot be obtained.

Acoustic Doppler Current Profiler (ADCP) Method

Acoustic Doppler Current Profiler (ADCP) has also emerged as a more advanced and easier method of monitoring coastal currents. ADCPs use the Doppler shift of sound waves to measure the velocities of water currents at different depths. They emit sound pulses into the water column. When the signals bounce off of water particles, the frequency shift of the echoed signals is used to calculate the water velocity. ADCPs have the ability to provide a snapshot of the structure of the currents from the surface to near the seabed. They are hence highly appropriate for studying the complex coastal currents near Bellingham.

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

ADCPs operate based on the Doppler effect. They are equipped with piezoelectric transducers that emit sound waves into the water. When the sound waves travel through particles such as plankton, sediment, or bubbles in the water, some of the sound energy is backscattered to the ADCP flow meter. The distance to the particles is estimated using the round-trip travel time of the sound waves to the particles.

The current velocity measurement is enabled by the Doppler shift. As the particles are transported by the water current, the frequency of the backscattered sound waves received by the ADCP will not be the same as the transmitted wave frequency. The magnitude of the frequency difference will be proportional to the water velocity along the acoustic path. In order to measure three-dimensional velocities, most ADCPs employ a minimum of three beams. Modern ADCPs also possess sensors like temperature sensors in order to take into account the effect of the temperature of the water on sound velocity, compasses to record the heading of the instrument, and pitch/roll sensors in order to get accurate measurements even during rough seas. The incoming signals are amplified, digitized, and processed to calculate an estimate of the current velocity at different depths.

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

In order to meet the requirements of high-quality measurement of coastal currents of Bellingham, the equipment should fulfill several conditions. The material of the equipment should be very reliable. The ADCP casing should be made of a material that can endure the tough conditions of the sea environment. The most suitable material is titanium alloy. It has high corrosion resistance, which is essential for long-term use in seawater. Titanium alloy is also strong and lightweight, so it is easier to handle and deploy. Its strength guarantees that the ADCP profiler can resist the mechanical stress of water flow and potential impacts from debris.

Size, weight, and power requirement are also essential. A lighter and compact ADCP is preferable since it is easily deployable on various platforms, e.g., small research vessels, buoys, or underwater remotely operated vehicles. Lower power consumption allows longer - term deployments, especially when powered by batteries. Cost is also another factor to consider. An inexpensive ADCP allows large - scale measurements, increasing the spatial and temporal resolution of the acquired data.

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

Mounting - Types

• Ship-mounted ADCP: Installed on a moving vessel, this gear is ideal for large-scale surveys of Bellingham coastal waters. As the ship travels, the ADCP can be continuously measuring the currents, with the outcome providing a large-scale image of the current regime.
• Bottom-mounted ADCP: Placed on the sea bed, it is suitable for fixed-point, long-term monitoring. It can be employed to provide useful information on the long-term trends and variability of the currents at a point.
• Buoy-mounted ADCP: These ADCPs are installed on a buoy and can track the water, which implies that measurements can be taken in areas where fixed-point measurements are not convenient. They are particularly well suited for use in areas of strong tidal currents or where a more mobile measurement system is desired.

Frequency Selection

The ADCP frequency will depend on the water depth. A 600kHz ADCP will be able to handle up to 70m of water depth. For Bellingham's relatively shallow nearshore waters, a 600kHz ADCP can provide highly detailed current profiles. A 300kHz ADCP would better serve for depths up to 110m. It offers greater range while having the accuracy level under control. Where the shallower waters are being addressed in the outer parts of Bellingham Bay or within the Salish Sea, a 75kHz ADCP is more preferable because it can penetrate deeper into the water column.

There are various known ADCP brands that exist in the market, such as Teledyne RDI, Nortek, and Sontek. However, for those wanting a cost-effective and high-quality option, the ADCP manufacturer China Sonar's PandaADCP highly recommended. Being made of all-titanium alloy, it is extremely hardy in sea conditions. Due to its superlative cost-performance ratio, it is the best option for researchers, coast planners, and those who need reliable current measuring data. Visit https://china-sonar.com/ for more.

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