How can Amanzimtoti coastal currents be measured?

1. Where is Amanzimtoti?

Amanzimtoti, a picturesque coastal town, is situated on the eastern coast of South Africa in the KwaZulu - Natal province. Occupying the Indian Ocean coastline, the town offers a peaceful blend of nature and vibrant coastal living. The name of the region "Amanzimtoti" is Zulu for "sweet waters" and is a dedication to the town's abundance of water as well as the cool sea breeze that caresses its shores.

The town coast is miles of lovely sandy beachlines along the warm waters of the Indian Ocean. The sand is golden in color and serves as the best spot for basking in the sun, water sports, swimming, and similar activities enjoyed by foreigners and nationals alike throughout the year. Away from the beach is thick coast cover that was in bloom and created a green oasis from the blue ocean. Amanzimtoti is also where the Toti River flows through the town and into the sea, forming an estuary of high biodiversity. The estuary is home to many species of fish, crustaceans, and birdlife and is thus an important ecological belt.

From a human perspective, Amanzimtoti boasts a well-developed community that lives in harmony with the sea. Fishing is one of the town's main industries, with small-scale fishermen venturing out to sea to catch a range of fish. The town offers a range of facilities for tourists and locals, including restaurants, shops, and accommodation. Its seaside location gives it a high level of traffic along the KwaZulu-Natal South Coast, and it is a big stopover for those traveling along the coast.

2. What are coastal currents around Amanzimtoti?

Coastal currents around Amanzimtoti are characterized by a complicated mix of different factors. Tides are one of the key driving forces, and the area is influenced by semi - diurnal tides caused by moon and sun gravity. These tidal cycles cause the water level to rise and fall twice a day, significantly affecting the flow of the water along the coast as well as in the Toti River Estuary. During high tide, water overflows onto the shores and estuary, raising the velocity of the current and reversing the direction of flow. With the departure of water at low tide, seaward water returns in and creates an ebb current which will carry sediment and nutrients.

Wind flow is also responsible for the regulation of coastal currents. The local prevailing winds, especially the southeasterly wind, are strong enough to form strong wind-driven currents. The winds, stronger in some seasons, force the surface water along the coast and affect the velocity and direction of the currents. More energetic surface currents are generated by stronger winds, which may interact with the tidal currents to produce more intricate patterns of flow such as eddies and upwelling areas. Upwelling, indeed, is an important process off Amanzimtoti since it brings cold, nutrient-rich water from deeper in the ocean towards near-surface waters, keeping the marine ecosystem productive.

The Amanzimtoti coastline topography, the estuary, and the continental shelf profile further alter coastal currents. The narrowed mouth of the Toti River Estuary has the potential to provide for a bottleneck, accelerating water flow when water enters or exits. Bottom irregularities and depth variation will cause currents to diverge, converge, or create circular current patterns. Aside from that, the freshwater discharge of the Toti River into the ocean will alter the salinity and density of the coastal waters and hence affect the buoyancy and circulation of the water masses, and hence the current structure as a whole.

3. How to observe the Amanzimtoti coastal water flow?

3.1 Surface Drifting Buoy Method

One of the classical methods of observing the coastal water flow off Amanzimtoti is through the use of surface drifting buoys. These buoys have GPS equipment that enables the scientists to track their trajectory over time. Once they are released in the ocean or into the estuary, the surface currents drive the buoys. By tracking the location of the buoys at regular time intervals, the scientists can map the trajectory of the water flow at the surface. This method provides rich data on direction and velocity of the surface current. It does, however, have a disadvantage. Wind - drag can significantly affect the movement of the buoys and introduce errors in the representation of the true current velocity, especially at greater depths. Also, surface drifting buoys send reports about the uppermost area of the water column only and do not report about the vertical structure of the currents.

3.2 Anchored Ship Method

The ship-anchored technique involves anchoring a ship in the sea off Amanzimtoti in a fixed location. Current meters are dropped from the anchored ship at varying depths in the water column. The current meters measure the speed and direction of the flow of water at specific depths. Several measurements made at varying depths over a prolonged period enable a profile of current velocity with depth to be achieved. This method gives accurate data about the existing conditions at a specific point in the water column. However, it is time - consuming and expensive since the ship has to be maintained in position for long periods. The presence of the ship can also disrupt the natural movement of water in the region, which could affect the accuracy of the readings.

3.3 Acoustic Doppler Current Profiler (ADCP) Method

Acoustic Doppler Current Profiler (ADCP) has seemed to be an improved and dependable method of surveying the nearshore currents in Amanzimtoti. ADCPs operate on the principle of sound waves to measure water velocities at different depths. The ADCPs have the ability to provide a well-integrated description of the current from the water surface to around - near - bottom levels and, therefore, providing detailed results regarding the three-dimensional flow field within the column of water. ADCPs can be deployed in various modes, such as on a traveling vessel (ship-mounted ADCP), anchored on the ocean bed (bottom-mounted ADCP), or on a floating buoy (buoy-mounted ADCP). Its adaptability allows it to measure over a broad scope of applications, ranging from great - scale monitoring of the complete coastal area to specific research studies of particular existing features within or near the estuary. Comparing to the past methods, ADCPs have the ability to take measurements of currents over an extended depth interval at once with high precision and are therefore a valuable instrument used in modern oceanography.

4. How does ADCPs work based on the Doppler principle?

ADCPs operate on the Doppler principle. They possess acoustic transducers that release sound pulses into the water at a specific frequency. When the sound pulses encounter small suspended particles within the water, such as sediment, plankton, or air bubbles, part of the sound energy is sent back to the ADCP.

If the particles are moving together with the water flow, the frequency of the sound pulses that are reflected will differ from the original pulses. This difference, the Doppler shift, is proportional to the velocity of the particles (and therefore the water). The ADCP measures the Doppler shift in each of its multiple acoustic beams (usually 3 - 4 beams in different directions).

For example, if the water is approaching the ADCP, the frequency of the sound backscattered will be higher than the emitted frequency, and if it is receding, the frequency will be lower. From the calculated mathematical algorithms and measured Doppler shifts from multiple beams, the ADCP is able to calculate the three-dimensional water velocity at different depths. The water column is divided into discrete layers, "bins," and the ADCP provides velocity measurements for each bin, constructing a reliable profile of the current velocity with depth.

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

High-quality measurement of the coastal currents off Amanzimtoti demands that the ADCP equipment meet a number of critical conditions. Material strength is of utmost importance, as the device needs to withstand the harsh marine environment that consists of saltwater exposure, temperature fluctuations, and mechanical stress. Titanium alloy is an ideal material for the ADCP casing. It possesses greater corrosion resistance, which will render the device functional in the corrosive saltwater environment for longer periods. Its strength - to - weight ratio is high, making the ADCP light yet strong, which is beneficial for ease of deployment, particularly in the harsh coastal and estuarine conditions around Amanzimtoti.

The ADCP must be small enough to allow easy deployment in the various coastal and estuarine environments around Amanzimtoti, e.g., narrow channels, shallow bays, and in the vicinity of the river mouth. Smaller size also reduces the device's impact on the natural water flow, minimizing potential measurement errors. Low power consumption is also relevant, especially when the ADCP is deployed in remote or autonomous setups. In the majority of cases, ADCPs are operated by batteries, and a low - power - consuming unit can operate for extended durations without constant battery replacement or recharging, offering uninterrupted and accurate data. Cost - effectiveness is also important, particularly for research studies, environmental monitoring programs, and small - scale operations. A cost-effective ADCP can be deployed to a larger area, covering a wider coastal zone and better appreciating the intricacies of current dynamics.

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

The right ADCP equipment to measure currents around Amanzimtoti depends on several factors.

6.1 By Method of Deployment

• Ship-mounted ADCP: Applicable to major surveying of the entire coastal zone and the water around the estuary, ship-mounted ADCPs are installed on a moving platform. While the ship travels along the area, the ADCP measures the current profiles underneath the ship, providing a general concept of the trends of currents in the area. This type of ADCP is suitable for the mapping of large-scale current patterns, the estimation of the impact of the estuary on the currents, and the study of the general circulation in the Amanzimtoti waters off the coast.
• Bottom - mounted ADCP: Tethered to the bottom, bottom - mounted ADCPs are used for long - term observation of current profiles at a single location. They are able to sample continuously over long durations, which is useful to investigate the long - term dynamics and variability of the coastal currents, e.g., seasonal cycles, the impact of environmental changes, and the development of characteristic current features in the area around the estuary or shipping lanes.
• Buoy-mounted ADCP: Installed on floating buoys, these ADCPs can be used to measure the surface and subsurface current flow in real-time. They are carried by the currents and therefore provide dynamic information about the flow as they move, which is particularly handy for monitoring the variability of the currents because of tides, wind, and freshwater inputs. This type of ADCP is perfect for monitoring the currents in the Toti River Estuary and other locations with complex flow regimes.

6.2 Frequency-based

The frequency of the ADCP is a very important parameter based on the water depth. In water depths ranging from around 70m, a 600kHz ADCP is a perfect choice. The higher frequency allows for more accurate measurements in shallower water and provides high-resolution data on the velocity of the current. For depths of about 110m, a 300kHz ADCP is recommended since it offers the best compromise between penetration depth and measurement accuracy. With increased water depth further, a lower frequency is required to penetrate the water column effectively. A 75kHz ADCP can be used for water depths of up to 1000m, enabling measurements in deeper waters where higher frequencies cannot penetrate.

There are only a couple of popular ADCP brands that have presence in the market, viz. Teledyne RDI, Nortek, and Sontek. However, for those budget-conscious, there is the ADCP manufacturer China Sonar's PandaADCP. It is made wholly of titanium alloy and performs pretty well without much expense. For price-sensitive individuals who want reliable ADCPs still, it makes a fine alternative. You may know more about them on their website: https://china-sonar.com/.

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