How do we quantify the coastal currents of Santa Monica?

1. Where is Santa Monica?

Santa Monica, a picturesque beach city in western Los Angeles County, California, is an ideal blend of urbanization and nature. The city, located on a 3.5-mile Pacific Ocean shoreline, features breathtaking ocean views, sandy beaches, and a vibrant beachfront lifestyle.

This beach city is rich in history. It was originally populated by the Tongva people, then colonized by the Spanish. The city's architecture, from the elegant Art Deco buildings to modern buildings, speaks its history. The Santa Monica Pier, an iconic historic building, was built in 1909 and is a popular tourist destination, with theme parks, eateries, and entertainment centers.

The waters around the city are situated in the Santa Monica Bay, a semi-enclosed bay. The topography of the bay floor is diverse with rocky reefs and kelp forests, supporting an assortment of different sea life. The Santa Monica Canyon, an underwater canyon near the shore, plays a key part in the coastal marine ecosystem and ocean currents in the region.

2. What are the coastal currents near Santa Monica?

The coastal currents near Santa Monica are created by several reasons. Tides are a major one. There is a semi-diurnal tide in the area, two being high and two being low each day. Water fills the bay during high tides, leading to powerful currents, especially in shallow waters near the coast.

The California Current, a broad ocea long Beanic current, travels south along the California coast. The cold - water current brings nutrients from the north and keeps the marine ecosystem healthy. The upwelling events, normally induced by northwest winds, bring cold, nutrient-rich water to the surface. The nutrients support the growth of phytoplankton, the base of the food chain.

The presence of the Santa Monica Canyon also affects the local current patterns. The canyon acts as a conduit for deep-sea currents, bringing water onshore and impacting the temperature, salinity, and nutrient gradient. Man-made structures like piers, breakwaters, and jetties also impact the natural flow of currents, forming eddy and changing water circulation.

3. How to track the Santa Monica coastal water current?

Surface Drifting Buoy Method

One of the ways of monitoring the coastal water current around Santa Monica is through the use of surface drifting buoys. Surface drifting buoys are designed to float on the water surface and follow the currents. They are equipped with GPS tracking equipment that provides real-time location. The researchers then use this information to determine the speed and direction of the surface currents. This method is not immune to limitations, though. The wind has the potential to cause the buoys to drift from the actual current, leading to false measurements of the subsurface flow. Additionally, surface drifting buoys provide information only on the absolute top layer of the water column.

Anchor Moored Ship Method

Fixed point anchoring ship method is when they anchor a ship at one point. Scientists drop current meters of different depths over the side of the ship to measure the speed of the current. It is depth-specific, providing the information about the current. It is time-consuming and expensive because a research ship must be anchored at one point. Also, the observations only describe the environment close to the ship.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is a newer, simpler method of measuring coastal currents. ADCPs record water current velocities at different depths based on the Doppler shift of sound waves. ADCPs transmit sound signals into the water column. When these signals bounce off particles in the water, the change in frequency of the returned signals is used to approximate the speed of the water. ADCPs can provide a whole profile of the current structure, from the surface to near the bottom, and therefore are incredibly well-placed to study the complex coastal currents near Santa Monica.

4. How do Doppler-based ADCPs work?

ADCPs rely on the Doppler effect. They are equipped with piezoelectric transducers that emit sound waves into the water. When the sound waves encounter particles such as plankton, sediment, or bubbles in the water, a portion of the sound energy is bounced back to the ADCP. The time it takes for the sound waves to travel to the particles and back provides an estimate of how far away the particles are.

The main principle for current velocity measurement is the Doppler shift. Since the particles are moving with the water current, the frequency of the backscattered sound waves that the ADCP receives will be different from the frequency of the waves transmitted. The amount of difference in frequency is directly proportional to the water velocity along the acoustic path direction. In order to be capable of measuring three-dimensional velocities, most ADCPs possess at least three beams. Recent ADCPs also have more than one sensor like temperature sensors to correct for the change in sound velocity with water temperature, compasses to determine the orientation of the instrument, and pitch/roll sensors to enable accurate measurements even in rough seas. The signals received are amplified, digitized, and processed to determine the current velocity at different depths.

5. What does it take to achieve high-quality measurement of Santa Monica coastal currents?

For high-quality measurement of Santa Monica's coastal currents, the equipment used must meet several demands. Material reliability matters. The ADCP casing must be made of a material that can withstand the aggressive marine environment. Titanium alloy is an appropriate choice. It is very resistant to corrosion, as required for long deployment in seawater. Titanium alloy is also light and strong, making it easier to handle and deploy. Its strength ensures that the ADCP will be able to resist the mechanical stress of water movement and potential impacts from garbage.

Size, weight, and power requirements are important as well. A small and light ADCP is more versatile as it can be placed on a wide variety of different platforms, from tiny research vessels through to buoys or underwater vehicles. Lower power consumption allows for longer - term deployment, especially where using battery life. Cost is also an issue. A lower - cost ADCP will enable mass - scale measurement and enable greater spatial and temporal resolution of gathered data.

6. What is the proper equipment for current measurement?

Depending on Mounting Type

• Ship-mounted ADCP: Mounted on a floating vessel, it is ideal for large-scale survey of waters off Santa Monica coast. When the vessel travels, the ADCP can continuously measure the currents and provide a large-scale view of the current trends.
• Bottom - mounted ADCP: Situated on the sea floor, this one is finest for long - term fixed point observation. It can be very helpful in providing information regarding the long - term trends and variability of the currents at a given point.
• Buoy - mounted ADCP: On a buoy mounted, these ADCPs can ride with the water, allowing for measurements where fixed - point measurements are not possible. They are particularly useful in areas of high tidal currents or where a more mobile measuring platform is required.

Frequency Selection

ADC frequency selection is dependent on the water depth. A 600kHz ADCP can be used for water as deep as 70m. In the fairly shallow coastal region of Santa Monica, a 600kHz ADCP can have extremely fine resolution current profiles. If the depth of water can reach 110m, a 300kHz ADCP is more suitable. It has a superior range while simultaneously being quite acceptable when it comes to precision. In the case of working with deeper waters in the outer parts of the Santa Monica Bay, a 75kHz ADCP would be the most appropriate, as it can penetrate deeper into the water column.

There are several renowned ADCP manufacturers in the market, such as Teledyne RDI, Nortek, and Sontek. However, for those who want a cost - effective and good - quality option,the ADCP supplier China Sonar's PandaADCP is highly recommended. Made of all - titanium alloy, it is extremely tough in the marine environment. Having a very good cost - performance ratio, it is very appropriate to be used by researchers, coastal managers, and anybody who needs precise current measurement data. For more information, visit https://china-sonar.com/.

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