How can we quantify Olympia's coastal currents?

1. Where is Olympia?

Olympia, the state capital of Washington, is found at the south end of Puget Sound. It lies on Budd Inlet, a shallow inlet that opens inward, about 60 miles southwest of Seattle. The watery location of the city has greatly influenced Olympia's development as a hub of commerce, transportation, and government activities.

The area was originally inhabited by the Nisqually tribe. Their rich cultural heritage, deeply tied to land and sea, remains in local tradition, art, and geography names. European settlers came to the area in the mid - 19th century because the area had fertile soil, dense forests, and waterways. The development of Olympia was initially centered on logging, fishing, and agriculture. With time, Olympia developed into the state capital, and its economy was diversified to include government services, education, and tourism as key elements.

Budd Inlet, on which Olympia is located, belongs to the Puget Sound system. The inlet is characterized by a complicated bottom structure underwater. It has shallow nearshore areas with muddy and sandy bottoms close to the coast, while in the center there are deeper channels. The presence of tidal flats and underwater reefs is a unique condition that is conducive to a variety of marine life. From salmon and crabs to a variety of seabirds and sea mammals like seals and otters, the area is a crucial habitat.

2. What is the condition of the coastal currents around Olympia?

The coastal currents around Olympia are conditioned by natural and human-conditioned factors together. Tides also play a significant role. Puget Sound contains a mixed tidal regime with both semi-diurnal (two high and two low tides per day) and diurnal (one high and one low tide per day) elements. Tidal ranges are significant, with highs of 15 feet in some places. During high tides, water floods Budd Inlet, creating strong flood currents. As the tide recedes, ebb currents carry water back from the middle of Puget Sound out to the open sound. The tidal currents are particularly strong in the narrow parts of the inlet.

Stronger ocean currents in the area also influence local waters. Water flow through the Strait of Juan de Fuca, the connection between Puget Sound and the Pacific Ocean, affects Olympia coastal waters' temperature, salinity, and circulation of currents. Weather patterns, including the westerlies, can push the surface waters onshore, whereas hard easterlies can cause upwelling. Upwelling events introduce cold, nutrient-rich water to the surface, initiating phytoplankton blooms and supporting the entire marine food chain.

Human activities have also altered the natural current regime. The construction of marinas, docks, and seawalls along the Olympia waterfront has disrupted the natural circulation regime. These structures can generate local eddies, reverse water flow direction, and alter sediment and nutrient distribution. Furthermore, the presence of industrial plants and wastewater treatment plants in the area has the ability to introduce contaminants and change the quality of water, and thus the current regime.

3. Monitoring the coastal water flow of Olympia how to?

Surface Drifting Buoy Method

One of the means of tracking the coastal water flow near Olympia is through the use of surface drifting buoys. The buoys are designed to drift on the water's surface and track the currents. The buoys are equipped with GPS tracking units, which transmit real - time location data. Scientists analyze this data to determine the direction and speed of the surface currents. However, this method is not flawless. Wind will cause the buoys to drift away from the actual current and lead to spurious measurement of the subsurface flow. Additionally, surface drifting buoys provide only information about the very top part of the water column and only provide insight into the whole current structure.

Anchor Moored Ship Method

The anchor moored ship method involves mooring a ship to a fixed location. Researchers employ current meters along the side of the ship at different depths to measure the current velocity. It provides depth - specific information about the currents. It is theoretically possible, however, because it is time - consuming and is expensive and requires a research ship to be moored. The readings are also representative only of the area near the ship, and it is difficult to obtain a comprehensive picture of the coastal currents in a large area.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) has emerged as a more advanced and simpler method of measuring coastal currents. ADCPs make use of the Doppler effect of sound waves to measure water current velocities at different depths. They project sound signals into the water column. On reflection from particles in the water, the frequency shift of the reflected signals is utilized to calculate the water velocity. ADCPs are able to provide a full description of the current structure, from close to the surface to near the seabed. It renders them highly suitable for exploring the complex coastal currents off Olympia.

4. How do ADCPs using the Doppler principle work?

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

Doppler shift is the key to measuring present velocity. In the case of the particles being transported by the current of the water, the returned sound wave frequencies received by the ADCP will be dissimilar from those emitted waves. The magnitude of such a frequency disparity is in proportion to the speed of the water along the direction of propagation of the acoustics. To measure three-dimensional velocities, most ADCPs employ at least three beams. Modern ADCPs also incorporate multiple sensors, including temperature sensors to compensate for the effect of water temperature on sound velocity, compasses to determine the direction of the instrument, and pitch/roll sensors to ensure accurate measurements despite rough seas. The returns received are amplified, converted to digital, and processed to calculate the current velocity at several depths.

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

Equipment deployed to measure the coastal currents in Olympia must meet a variety of requirements for high-quality measurement. Material reliability is crucial. The ADCP casing must be made of material resistant to the corrosive marine environment. Titanium alloy is the best. It has a high degree of corrosion resistance, which is necessary for extended deployment in seawater. Titanium alloy is also hard and light, thus simple to handle and deploy. Its tensile strength guarantees that the ADCP current meter will be able to endure the mechanical stress of water flow and impacts from debris.

Size, weight, and power demands are also factors. A smaller and lighter ADCP is more versatile, in that it can be mounted on a broad variety of platforms, ranging from small research ships to buoys or underwater vehicles. Lower power consumption allows longer - term deployments, especially where batteries are employed. Cost is also a factor. A less costly ADCP permits large - scale measurements, which enhance the spatial and temporal resolution of the data being collected.

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

Types of Mounting

• Ship-mounted ADCP: Fixed on a traveling vessel, it is particularly appropriate for broad-scale surveys of Olympia's adjacent coastal waters. While the ship is in motion, the ADCP can record the currents continuously, providing a broad-scale sense of the current flows.
• Bottom - mounted ADCP: Installed on the seabed, this is ideal for fixed - point, long - term observations. It can provide useful information on the long - term trends and variability of the currents at a point.
• Buoy-mounted ADCP: Mounted on a buoy, these ADCPs are able to track with water movement, enabling measurement where fixed-point measurement is undesirable. In areas of high tidal currents, or in areas where a mobile measuring platform would be advantageous, they are especially valuable.

Frequency Selection

The ADCP's frequency selection is water depth dependent. A 600kHz ADCP will be suitable for water depths up to 70m. In the comparatively shallow coastal waters off Olympia, a 600kHz ADCP will give very good current profiles. For water depths up to 110m, a 300kHz ADCP would be better suited. It has a greater range while also giving a good amount of accuracy. When operating in the deeper waters of the central Puget Sound, a 75kHz ADCP is the choice of preference since it excises deeper into the water column.

There are a lot of well-established brands of ADCPs that are on the market, among them being Teledyne RDI, Nortek, and Sontek. However, if a person wants something affordable but good quality, the ADCP manufacturer China Sonar's PandaADCP is as good as any. Completely made of all - titanium alloy, it is more durable in the marine environment. With a great cost - performance ratio, it is an excellent choice for researchers, coastal managers, and anyone who needs reliable current measurement data. For more information, visit https://china-sonar.com/.

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