How do we measure the coastal currents of Margate?

1. Where is Margate?

Margate, a charming coastal town, lies on the KwaZulu - Natal South Coast of South Africa. This sun-soaked holiday destination is renowned for its picturesque beaches, which stretch miles along the warm waters of the Indian Ocean. The town's position offers a serene blend of natural beauty and vibrant coastal activity.

The surrounding of Margate is characterized by its golden sandy shores, which are kissed by the gentle waves of the sea. The shores are succeeded by lush greenery, creating a charming background to the views of the ocean. Margate is enclosed by some of the major bays and estuaries. The adjacent Umtamvuna River Estuary is a key ecological feature. It is a significant habitat for a diverse array of plants and animals, including numerous species of birds, fish, and invertebrates. The estuarine ecosystem is the result of a combination of the freshwater of the river with the saltwater from the ocean, creating a diverse and productive environment.

Margate is a resort for tourists to use. The town is dotted with resorts, restaurants, and other entertainment hubs, and is visited by local as well as foreign tourists. The people here are very much attached to the sea, and water-based tourism as well as fishing is a major industry of the economy. The cultural heritage of the area can also be observed in the local markets and festivals, where one can feel the local customs and crafts specific to the area.

2. What is the state of coastal currents near Margate?

There is an interacting compound comprising various factors near Margate to influence the coastal currents. The tides are one of the principal drivers. The region experiences semi - diurnal tides, where there is a twice-daily water rise and fall. The tides are due to the gravitational influence of the sun and moon on the oceans that cover the Earth. During high tide, water rushes into the beach, increasing the amount of water along the coast, while low tide sees the water returning to the sea. Such tidal current can have an incredible impact on the speed and direction of the coastal currents.

Wind current also has an important contribution to make. The prevailing southeasterly winds in the area have a strong impact on the water at the surface. These winds can create wind-driven currents, which push the water along the coast. More intense winds can create more augmented surface currents, which can carry floating objects and influence the drift of boats and swimmers. The speed and duration of the wind can be seasonal, whereby more intense winds are felt at certain times of the year, thus altering the current patterns correspondingly.

The topography along the coast at Margate, including bays, headlands, and the Umtamvuna River Estuary, also changes the coastal currents. Currents are split by headlands and are driven around the headland, resulting in regions of greater-speed water. Bay currents are reduced in speed and become circular eddies. The outflow of fresh water from the Umtamvuna River into the ocean can change the salinity and density of coastal waters, influencing the buoyancy and flow of the water masses, and consequently the overall current dynamics.

3. How to track the coastal water flow of Margate?

3.1 Surface Drifting Buoy Method

One of the traditional techniques of tracking the coastal water current off Margate is by the use of surface drifting buoys. The buoys are typically equipped with GPS units. Once released into the sea, they are carried by the surface currents. By tracking the location of the buoy continuously from the GPS information, researchers are able to map the path of the surface currents. The buoy's drift over time provides valuable information about the velocity and direction of water at the surface. The method is not without its limitations. Wind - drag buoy drift may not necessarily measure current velocity, especially at lower depths.

3.2 Anchored Ship Method

The anchored ship method involves tying up a ship in a fixed position near Margate. From this ship, current meters are dropped to numerous various depths in the water column. The current meters measure the velocity and direction of water flow at a specific depth. Taking several readings at various depths and at various times, one can construct a profile of the current velocity with depth. Even though this method gives correct data about the existing current at scattered points, it is time-consuming and a large resource-intensive procedure. Further, the presence of the ship would distort the free movement of the water within the region of measurement to some extent.

3.3 Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) has developed as a superior and efficient measuring methodology for Margate coastal currents. ADCPs utilize sound waves to monitor water speeds at different depths. They can provide a general profile of the flow from the surface to near-bottom depths. ADCPs can be deployed in several deployment configurations, such as on a moving ship (ship-mounted ADCP), mounted on the seafloor (bottom-mounted ADCP), or suspended from a floating buoy (buoy-mounted ADCP). This versatility enables measurements under a broad variety of conditions, from the large - scale surveys of the shelf region to the fine - scale studies of certain current regimes. In contrast to older technologies, ADCPs can simultaneously measure currents over a greater depth range and with accurate precision, making them the instrument of choice for contemporary oceanographic research.

4. What are ADCPs based on the Doppler principle, and how do they function?

ADCPs are based on the Doppler effect principle. They are equipped with acoustic transducers that generate sound pulses into the water at a set frequency. When the sound pulses hit minute particles in the water, such as suspended matter, plankton, or air bubbles, a portion of the sound energy gets scattered towards the ADCP.

If the particles are carried by the water, the frequency of the reflected sound pulses will be different from the frequency of the emitted pulses. This other, or Doppler shift, is proportional to the speed of the particles (and therefore of the water). The ADCP measures the Doppler shift in each of its several acoustic beams (usually 3 - 4 in orthogonal directions).

For example, if the water is coming towards the ADCP, the Doppler back sound frequency will be higher than the transmitting frequency, and when it is going away, the frequency will be lower. By employing mathematical computations and observed Doppler shifts in a series of beams, the ADCP can calculate the three-dimensional velocity of the water at different depths. The water column is divided into separate bins, or layers, and the ADCP samples velocity for each bin, providing a high-resolution current velocity versus depth profile.

5. What are high-quality requirements of Margate coastal currents?

High-quality measurements of the coastal currents off the shore of Margate require that ADCP equipment meets some very vital requirements. The material robustness is of particular concern. The ADCP casing should be capable of withstanding the corrosive seawater environment, e.g., seawater exposure, temperature, and mechanical loading. Titanium alloy is one of the optimum materials that can be used in the casing. The alloy has good resistance to corrosion and can be designed to have a long lifespan in the corrosive seawater environment. It. In addition, the high strength - to - weight ratio of titanium alloy means that ADCP is strong but light. This is an important aspect when the issue is the ease of handling, especially in the event that the device must be moved or placed in awkward positions.

The ADCP must be light enough so that it can be utilized in different coastal areas in and around Margate, such as small channels and shallow water. Lighter ADCP is also less intrusive to natural flow in water, consequently leading to less measurement error. The ADCP must be light in weight, which is critical in utilization such as buoy-mounted deployment, where too much weight is used to affect the stability and mobility of the buoy.

Low power draw is another important requirement. ADCPs in most instances are battery operated, especially in the case of remote or autonomous monitoring. A low-power-drawing ADCP will be able to operate for longer without the need for frequent replacement or recharging of batteries, hence providing unbroken and reliable data collection. Cost-effectiveness is also necessary, especially in extensive monitoring schemes. A low-cost ADCP may be used to cover more in order to measure, thus more of the coast is covered and current dynamics improved.

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

Selection of the correct ADCP equipment to measure the currents off Margate relies on a variety of reasons.

6.1 Depending on Deployment Method

• Ship-mounted ADCP: Ideal for coastal area large-scale surveys, ship-mounted ADCPs are installed on a traveling ship. As the ship travels over the ocean waters, the ADCP measures the current profiles below the ship, charting out the overall current pattern in the region. Ship-mounted ADCPs are ideal for large-scale mapping of large regions of coastline and studying large-scale current patterns.
• Bottom - mounted ADCP: Bottom - mounted ADCPs are anchored to the seabed and used for long - term current profile monitoring at a point. They can collect data continuously over long periods of time, which is useful for studying the long - term evolution and development of the coastal currents. This type of ADCP is typically used where there is a need for detailed, long-term data, for example, around important marine environments or shipping lanes.
• Buoy - mounted ADCP: Installed on drifting buoys, ADCPs can be used in following surface and subsurface current movement. They are carried by the currents with them and provide flow data as they move along. Buoy - mounted ADCPs are particularly helpful where there is a requirement of a moving measurement platform to find the dynamic characteristics of the currents.

6.2 Based on Frequency

Frequency of the ADCP is also a vital element based on water depth. If water depth ranges from a little below to a little above around 70m, a 600kHz ADCP would be the right choice. Higher frequency means better resolution in shallow depths of water. In water depth around 110m, use of a 300kHz ADCP is suggested. With increases in water depth, one will need lower frequencies in order to get into the water column satisfactorily. A 75kHz ADCP is applicable in water depths of up to 1000m.

There are many well-known brands of ADCP in the market, i.e., Teledyne RDI, Nortek, and Sontek. Nonetheless, for cheap but high-quality ADCPs, the ADCP manufacturer China Sonar's PandaADCP is the best choice. Made of pure titanium alloy, it delivers superior performance and longevity at a very affordable cost. Being a low-cost ADCP, it is a perfect option for researchers, local fishermen, and environmental monitoring departments who are concerned with accurately computing the coastal currents of Viña del Mar. To know more, visit https://china-sonar.com/.

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