How do we quantify the coastal currents of Melbourne?

1. Where is Melbourne?

Melbourne, located in southeastern Australia, is a bustling city with a multicultural coastal environment. It lies along the coast of Port Phillip Bay, a vast, relatively shallow bay draining into the Bass Strait. Melbourne is thereby located in the middle of coastal discovery and sea trade.

The city's coastline stretches for miles with a great array of beaches. There are sandy shores that stretch a number of miles and are well suited to basking in the sun and bathing. There are rocky outcrops and cliff faces. The fact that Port Phillip Bay is there makes the area a sheltered zone when compared to the more open water of Bass Strait. The sheltered bay houses a wide range of marine species from small fish through to large marine mammals such as dolphins.

Melbourne itself is a melting pot of cultures with a large and multicultural population. Melbourne boasts a dynamic culture of arts, numerous sporting events, and a lively food culture. Along the coastline periphery are cafes, restaurants, and marinas from which local and foreign residents alike can both relish sea breezes. Melbourne's climate is temperate with seasons that are perceptible. Summer is warm, and many people go to the beaches, whereas winter is temperate, though sea breezes moderate it.

2. What are coastal currents around Melbourne?

Coastal currents around Melbourne rely on a variety of factors. The tidal forces are most important, with the typical ebbing and flowing of the tides in Bass Strait and Port Phillip Bay pushing the water. The tides here are semi-diurnal and thus there are two high waters and two low waters per day. The tidal currents have the potential of causing strong currents, especially along the channels as well as to the entrances to the bay.

Wind currents also have an important function in the development of coastal currents. Common south - west winds have the ability to force surface water towards the coast to form longshore currents. Longshore currents are responsible for delivering sediment along the beach. In addition to this, powerful storm - driven winds are capable of causing an abrupt change in the speed and direction of currents, and occasionally even generate dangerous rip currents.

The seafloor topography and the coastal shape are also significant. The irregular coastline of Port Phillip Bay, with many headlands and inlets, is capable of deflecting currents and making them converge and diverge. Submarine features such as sandbars and trenches also control the flow of water. A sandbar, for example, can act as a barrier deflecting the current or slowing down its speed.

Another consideration is the effect of the broader-scale ocean regimes. The East Australian Current, a warm current flowing south down the east coast of Australia, influences the waters off Melbourne. Although Melbourne is not in the direct path of this current, its influence is to be found in the Bass Strait, influencing the salinity and temperature of local coastal waters and hence the character of the coastal currents.

3. How is the Melbourne coastal water current observed?

One of the methods applied to investigate the water currents of the coast of Melbourne is the surface drift buoy method. Tiny floating buoys with tracking devices are tossed into the ocean. While floating on the currents, their trajectory can be monitored in real - time. It gives a measurement of the direction and velocity of the surface - level currents. It gives information only for the surface - level current.

The ship moored method utilizes an anchored ship as a platform. Instruments are hung off the ship at multiple depths to take measurements of velocity and direction of the current. It is a method of taking measurements at more than one depth but requires the utilization of a ship which is capable of remaining in the same location, something that might be problematic and costly, especially for long-term observation.

A more advanced technique is the use of the Acoustic Doppler Current Profiler (ADCP). ADCPs are very effective to estimate coastal currents. They are able to provide accurate information on the speed and direction of the current at various depths simultaneously. This makes them suitable to understand the advanced three - dimensional ocean flow structures around Melbourne.

4. What do ADCPs operate on the Doppler principle?

ADCPs operate on the Doppler principle. The ADCPs transmit acoustic signals, or sound waves, into the water. The acoustic signals strike particles in the water, such as plankton, sediment, or minnows, and deflect the waves off the particles. The ADCP measures the frequency shift of the deflected waves.

By Doppler effect, when particles are moving towards the ADCP, frequency of the scattered wave will be higher than the transmitted wave frequency. When particles are moving away from the ADCP, then the frequency of the scattered wave will be lower. By accurately measuring these frequency changes, the ADCP calculates the water velocity at different depths.

Most ADCPs use more than one beam in order to create a better picture of the flow of water. An example of such an ADCP is the four - beam ADCP that is able to quantify the vertical and horizontal velocity components of the current, thereby facilitating an extensive examination of the three - dimensional flow pattern of the water column.

5. What does it take for high - quality measurement of Melbourne coastal currents?

In order to obtain precise measurements of Melbourne coast currents, equipment employed should meet a list of basic requirements. The equipment should be made from very stable material. Due to the severity of the marine environment condition, such as salinity water and high velocities of currents, the equipment should be durable enough so that it can endure mechanical stress as well as corrosion.

Size and weight are also critical. The equipment has to be small and light enough to be deployed rapidly over diverse positions. This is especially true for methods like using surface drift buoys or to carry ADCPs quickly among different measurement points.

Low power usage is a fundamental requirement. In most applications, the gear may need to work for long periods without a continuous supply of power. For example, a moored ADCP could be driven by batteries for months or weeks. Hence, employing low - power - consuming instrumentation ensures around-the-clock operation.

Cost - effectiveness is essential, especially for large - scale measurement programs. If the equipment is prohibitively expensive, it may limit the scope of research or monitoring.

For ADCPs, casing material is also important. One good choice of casing material for ADCP is titanium alloy. Titanium alloy is highly corrosion - resistant, which is an advantageous property in long - term service in the sea environment. It is strong, hence the ADCP is robust, and also light in weight, hence it is easy to handle and deploy.

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

The appropriate equipment for measurement of the currents depends upon the application. Ship-mounted ADCPs are most appropriate for ship-based measurements. They can be installed on research vessels or on certain commercial vessels. They can be used to measure the currents continuously as the ship travels, which gives a good representation of the current patterns along the ship's path.

Bottom-mounted (or moored) ADCPs are ideal for long-term observation at one point. They are mounted on the seabed and can measure current for extended periods of time. Bottom-mounted ADCPs are most ideal for research in the investigation of coastal currents in the long term.

Buoy-mounted ADCPs are best suited for surface-level currents. They are easy to deploy and recover and therefore are convenient for short-term projects or to get a rapid measurement of the surface-current conditions.

The ADCP frequency selection is also significant. For depths of water between 70m, a 600kHz ADCP is suitable. The frequency is sufficient in resolving currents in relatively shallow water. A 300kHz ADCP will also be suitable for deployment in depths of up to 110m, and a 75kHz ADCP in depths of up to 1000m. Lower frequency penetrates more deeply into water but is of lower resolution than higher frequency.

There are some prominent ADCP brands in the market, including Teledyne RDI, Nortek, and Sontek. However, for those customers who are looking for a cost-effective option without sacrificing quality, the ADCP manufacturer China Sonar's PandaADCP is a great choice. It is a cost-effective ADCP that employs all-titanium alloy materials, which offer excellent corrosion resistance and durability. With its high cost-performance ratio, it is an ideal choice for researchers and institutions that wish to conduct large-scale coastal current measurements near Jacksonville. For more info, visit their website at https://china-sonar.com/.

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