How are Oranjemund coastal currents to be measured?

1. Where is Oranjemund?

Oranjemund is a unique seacoast town in the southwestern part of Namibia in the Kunene Region located directly on the border with South Africa. Oranjemund is unique, as it has its own specific identity shaped by the past and environment. Historically, the development of Oranjemund is directly associated with diamond mining. The town exists to provide services for the large-scale diamond - mining activities in the area, and signs of this mining industry can be observed in society and infrastructure.

The landscape around Oranjemund is a stark mixture of empty desert and the cold, crashing waves of the Atlantic Ocean. The Namib Desert, one of the oldest deserts in the world, stretches behind the town, offering a stark contrast to the sea. The town's coastline is rimmed with miles of sandy beach that seem to stretch on forever, broken by rocky outcrops and tiny, sheltered bays.

The local population in Oranjemund is small but compact. Diamond mining remains a significant part of the local economy, with numerous locals working through mining. Besides mining, fishing is also an activity that takes place, with locals fishing in the coastal waters to catch fish of various kinds. Isolation has provided the town with the feel of self-containment, with numerous local services and facilities serving its people.

Geographically, Oranjemund is situated in an area that is strongly influenced by the cold Benguela Current. This current flows northwards along the west coast of southern Africa, bearing cold, nutrient-rich water. The interaction of the Benguela Current with the local topography creates a productive marine ecosystem off the coast of Oranjemund, comprising a diverse array of marine life, ranging from fish and crustaceans to seals and seabirds. The seabed around Oranjemund varies from shallow close to shore, and generally sandy, to deeper channels away from land, with a more diverse underwater landscape.

2. How are the coastal currents off Oranjemund?

The coastal currents off Oranjemund are dominated by the Benguela Current. The powerful ocean current is the major driver of the local marine life. The Benguela Current upwells cold deep- water, which provides a consistent supply of nutrients to the surface. The nutrient-rich water drives the productivity of phytoplankton, the base of a healthy and high- quality marine food web. The intensity and direction of the Benguela Current could vary seasonally based on large - scale atmospheric and oceanic conditions. Changes in wind patterns, for example, can alter the direction and speed of the current, affecting the coastal waters in the area.

Wind is also an important factor controlling the coastal currents off Oranjemund. The prevailing south - easterlies blow over the region during most of the year. The winds can drive surface waters, creating wind-driven currents that interact with the Benguela Current. Stronger winds can accelerate the surface currents and reverse their direction, producing complex patterns of flow. The headlands and inlets of the coastline of Oranjemund further distort these currents. Headlands can accelerate currents as water is diverted around them, and inlets can form areas of eddies and relatively calm water where current flow is more complex.

Tides also contribute to the coastal currents off Oranjemund, although their influence is generally secondary to that of the Benguela Current and wind - forced currents. The region experiences semi - diurnal tides, which cause the sea level to rise and fall twice a day. These tidal currents create other currents which co - operate with the prevailing flow regimes, especially in the shallow bays and near the coast. The combination of tides, wind, and the Benguela Current generates a dynamic and intricate system of coastal currents along the Oranjemund coast.

3. How to measure the Oranjemund coastal water flow?

Surface Drift Buoy Method

One traditional method for measuring Oranjemund coastal water flow is by using surface drift buoys. The buoys are equipped with GPS tracking devices. When deployed in the ocean, they float on the surface and are carried by the surface currents. Based on the movement of the buoys over time from the GPS data, scientists can determine the direction and speed of the surface-level currents. But this method has its limitations. It provides information only for the top layer of the water column and could be strongly biased by wind-induced drift, which may not be indicative of the true underlying current flow. Further, in the often - rough waters off the coast of Oranjemund, surface drift buoys are readily moved, crushed by waves, or impacted by floating debris, and information recorded is less reliable.

Moored Ship Method

The ship mooring method is the act of mooring a ship in a single location near the Oranjemund coast. Current-measuring instruments such as current meters are then lowered from this ship at varying depths. These instruments measure the direction and speed of the current at each depth, allowing it to be possible to get a vertical profile of the current. While the method may give an accurate piece of information at a certain point, its spatial extent is limited to around the ship that is docked. Furthermore, the ship will tend to disturb the natural flow of currents in the region. The ship movement, and also the turbulence produced by its engines, can affect the accuracy of measurements and hence has to be removed while interpreting data.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) has turned out to be a more advanced and efficient tool for measuring coastal currents in Oranjemund. ADCPs are highly appreciated in oceanographic studies since they are capable of measuring the current velocities at multiple depths in a large volume of water at the same time. With this technology, scientists are able to obtain a complete description of the three - dimensional current structure, which is required to model the complex coastal circulation induced by the Benguela Current, wind, and tides accurately in Oranjemund. In contrast to conventional approaches, ADCPs are able to instantly and precisely gauge currents at various depths, offering important information regarding the varying vertical and horizontal distribution of the currents in the coastal waters of the region. This enables researchers to observe the complex interactions between various current components and their effects on the surrounding marine life.

4. What is the principle behind ADCPs using the Doppler principle?

ADCPs work on the basis of the Doppler effect. The device introduces acoustic pulses, or sound waves, into the water column. When the sound waves travel through suspended small particles in the water, such as plankton, sediment, or bubbles, some of the energy in the sound waves will be deflected towards the ADCP. Should the particles be moving with the current, then the frequency of the backscattered sound waves will be altered compared to the frequency of the emitted sound waves. This shift in frequency, known as the Doppler shift, is directly proportional to the particles' velocity, and thus the current velocity.

Most ADCPs consist of more than one transducer beam, three or four most commonly, which are directed at a range of directions. By measuring the Doppler shifts in each beam, the ADCP will be capable of calculating the velocity components of the current in three-dimensional space. The instrument splits the column of water into individual depth bins and, for each bin, calculates the current velocity. This allows ADCPs to generate a detailed profile of current velocity as a function of depth. For example, it can show how the speed near the surface shifts from being largely wind-driven to more driven by the Benguela Current in the deeper layers. Such detailed information is invaluable in interpreting the complex flow dynamics of the coastal waters off Oranjemund.

5. What's needed for high-quality measurement of Oranjemund coastal currents?

For offering high-quality measurement of the Oranjemund coastal currents, the measuring equipment must meet a series of fundamental conditions. Material reliability is given top priority because the equipment is to be exposed to the harsh marine environment. The cold and salty seawaters along the coast of Oranjemund and the abrasive nature of sand carried by wind from the surrounding desert are extremely harsh to the survival of the equipment. The gear must consist of materials that are resistant to corrosion, erosion, and biofouling, especially in the case of ADCPs.

The gear size should be minimal in order to provide a lesser impact on the natural flow of current and facilitate easy deployment in a broad array of positions, such as shallow nearshore areas and deeper channels offshore. Light equipment is also preferred, as it facilitates easier deployment and recovery, especially in the often - inclement coastal conditions off Oranjemund. Low power utilization is also essential, especially in the event of long - term deployments, owing to the likely limitability of power supplies in the remote coastal environment.

Cost - effectiveness is a second critical factor, especially where large - scale measurements are in question. High-cost sensors may limit the number of sensors that can be employed, lowering the spatial extent of the measurements. For ADCPs, a titanium alloy enclosure is a perfect choice. Titanium alloy possesses excellent saltwater corrosion resistance and sand particle erosion resistance. It is also hard and light, which is perfect for use in the severe environment off Oranjemund. Although a high-performance material, technological advances in manufacturing have reduced the cost of titanium alloy-cased ADCPs, and they are now a viable choice for large-scale coastal current monitoring in the area.

6. How to Select the Appropriate Equipment for Current Measurement?

The selection of the appropriate equipment for measuring currents in Oranjemund is application-specific.

Types of ADCPs Based on Use

• Ship-mounted ADCP: Installed on a traveling ship, this ship-mounted ADCP is the most suitable ADCP for broad-scale surveys of the Oranjemund coastal waters. As the ship traverses the region, the ADCP can continuously take measurements of the currents along its travel route, providing a wide-scale picture of the current behavior influenced by the Benguela Current and wind. This is utilized in operations such as marine navigation, understanding the overall circulation of the waters around the area, and for fisheries management, helping to identify areas with favorable fishing conditions.
• Bottom - mounted (Sit - on - the - bottom) ADCP: Installed on the seafloor, these ADCPs are employed for fixed - point, long - term measurements. They can be stationed in a position for extended durations, gaining knowledge of currents at that location. This type of ADCP comes in handy while studying the localized, fine-scale current behavior, e.g., the effect of underwater topography on the current flowing and changing pattern over time. This information is valuable for ecological research, environmental monitoring, and understanding the impact of anthropogenic activities, i.e., diamond mining, on the marine ecosystem.
• Advanced Buoy-mounted ADCP: Installed on a float buoy, these ADCPs can drift with the current, recording velocity at multiple depths while going with the flow. They are specifically ideal for observing synoptic, large-scale current patterns in open ocean waters outside Oranjemund or for tracking the movement of water masses with the control of the Benguela Current in a large region. This type of ADCP can potentially provide valuable data for the prediction of the spread of pollutants, the migration of marine life, and the health of the whole marine ecosystem.

Frequency Selection

The ADCP frequency must be chosen with caution based on the water depth. A 600kHz ADCP would be suitable for a water depth of up to about 70m, and would provide high-resolution measurements in comparatively shallow water near the Oranjemund coast. This frequency would be ideal for studying the near-shore current flow patterns and tides and wind influences in the shallower waters. For a depth of approximately 110m, a 300kHz ADCP flow meter would be an appropriate option because the sound wave penetrates deeper into the water column yet maintains acceptable measurement precision. This can be utilized to explore the mid-depth layers of the water column where the transition from surface and deeper currents occurs. In extremely deep waters, ranging from 1000m, a 75kHz ADCP is normally employed, which can be used in the deeper channels along the Oranjemund coast, enabling one to understand the flow dynamics in the deeper aspects of the ocean.

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.