How do we measure the coastal currents of Port Nolloth?

1. Where is Port Nolloth?

Port Nolloth is a small beach village situated on the west coast of South Africa in the province of Northern Cape. The remote town hugs the rocky coastline upon which the frigid waters of the Atlantic Ocean meet the arid reach of the Namib Desert. The landscape of the town is formed by extensive, sandy beaches that are scattered with rocky outcrops, and its shoreline is endowed with scenic ocean views of the vast stretch of ocean.

Port Nolloth has a small but working local population, whose existence is firmly rooted at sea. The local economy has been sustained by fishing for generations. Port Nolloth's harbor is a busy community, with daily leave-takings of fishing vessels with a cargo of various marine life such as hake, snoek, and crayfish. These catches not only sustain the local community but also nourish the country's seafood economy. In addition to fishing, the town has a certain appeal that attracts tourists seeking its unspoiled natural environment, wildlife, and the potential for a slower-pace coastal lifestyle.

Port Nolloth is geographically located in an area dominated by the cold Benguela Current. This dense ocean current flows northwards along the west coast of southern Africa, bearing cold, nutrient - rich water. The interaction between the Benguela Current and the local topography creates dense marine biodiversity off Port Nolloth coast. Off the town, the seabed varies from sandy flats inshore to deeper channels further out, supporting an array of marine life from shellfish and rainbow-hued fish through seabirds and seals. The nearby Richtersveld National Park, created a UNESCO World Heritage site, adds to the region's significance ecologically through its desert - coast interface.

2. What is the condition of the coastal currents near Port Nolloth?

Coastal currents near Port Nolloth are mainly influenced by the Benguela Current. Cold, upwelling current, it is that which is the primary force to push the immediate marine conditions, and it is the greatest, sole influence in this environment. It carries with it the cold, deep-water onto the shores but also, through the flow, nutrients supporting an effective system to the sea. Phytoplankton blooms are common in these nutrient-rich waters, which form the base of the marine food chain and attract various fish, whales, and other marine life.

Wind is also a significant force shaping the coastal currents off Port Nolloth. Prevailing south-easterly winds sweep across the region for much of the year. These winds have the power to drive surface waters, creating wind-driven currents that intersect with the Benguela Current. Strong winds could enhance the surface current speed and alter the direction of currents so that they produce complex flow patterns. Bays and headlands along the Port Nolloth coast also deflect the currents. Headlands will speed up the currents as water is deflected around them, while bays create areas of eddies and relatively stagnant water where the current flow is more complicated.

Tides also contribute to the coastal currents off Port Nolloth, but in many cases are dominated by the preponderant Benguela Current and wind - driven currents. Semi - diurnal tides prevail in the area and cause the sealevel to rise and fall twice daily. These tidal currents produce secondary currents which interact with the dominant flow regimes, especially in the shallow coastal areas near the shore and the bays. The interaction among tides, wind, and the Benguela Current creates an active and changing system of coastal currents off Port Nolloth.

3. How to observe the coastal water flow of Port Nolloth?

Surface Drift Buoy Method

One of the classic means of observing the coastal water current at Port Nolloth is through the use of surface drift buoys. GPS tracking devices are installed in the buoys. Upon being thrown into the water, the buoys are carried by the surface currents. By observing the displacement of the buoys over a period of time with the aid of the GPS data, scientists are able to determine the direction and speed of the surface - level currents. However, this method has limitations. It only provides information for the surface layer of the water column and could be significantly affected by wind-driven motion, which could not always be representative of the true current flow beneath. Also, in the often - turbulent waters off the coast of Port Nolloth, surface drift buoys are easily displaced, wave - damaged, or influenced by floating rubbish, reducing the quality of the data.

Moored Ship Method

The moored ship method involves mooring a ship in a fixed position off the coast of Port Nolloth. Current - measuring instruments such as current meters are dropped from this ship at different depths. These sensors find the current speed and direction at every depth, allowing a vertical current profile to be built. While precise data for a single point might be available, this method can only cover restricted area around the ship at sea. Furthermore, the presence of the moored ship could well disturb naturally occurring current pattern in the environment. The ship's movement will, in addition, affect the accuracy of the measurements, and there will be the turbulence created by the engines that will also affect the accuracy of measurements, requiring accurate calibration and data correction.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) has since become an advanced and efficient way of measuring coastal currents in Port Nolloth. ADCPs are highly prized for oceanographic research due to the fact that they are able to measure current velocities at more than one depth simultaneously over a large body of water. Scientists can obtain an all-encompassing appreciation of the three-dimensional pattern of the current with this technology, which is essential for accurate modeling of the complex coastal circulation pattern induced by the Benguela Current, wind, and tides in Port Nolloth. In contrast to conventional techniques, ADCPs are able to measure currents at various depths rapidly and precisely, giving useful information on how the currents change vertically and horizontally in the coastal waters of the region. This allows for the investigation of the complex interactions between various current components and their effect on the local marine environment.

4. How do ADCPs operating on the Doppler principle function?

ADCPs function on the principle of the Doppler effect. The instrument emits acoustic pulses, or sound waves, into the water column. As these sound waves travel through tiny particles suspended in the water, such as plankton, sediment, or bubbles, some of the sound energy gets scattered in the direction of the ADCP. If the particles are moving in the direction of the current, the frequency of the scattered sound waves will be different from the frequency of the emitted waves. This.uence change, which is referred to as the Doppler shift, is proportional to the velocity. of the particles and hence also to the current. velocity.

. Most ADCPs contain more than one transducer beam,. generally three. or four, oriented at different angles. By measuring the Doppler shifts. in all beams, the ADCP calculates. the current. velocity components in. three. dimensional space. The instrument sectionally divides the water column into separate bins of depth, and for each bin, it computes the current velocity. This, in turn, allows ADCPs to produce a clear profile of the current velocity with depth. For example, it can show how current velocity changes from the surface, where wind dominates, to the deeper layers regulated by the Benguela Current, presenting a clear picture of the current behavior in Port Nolloth coastal waters.

5. What's required for high - quality measurement of Port Nolloth coastal currents

To accurately measure Port Nolloth's coastal currents, the measuring equipment must meet a number of important requirements. Material reliability is most critical since the equipment will be exposed to the corrosive sea environment. The cold, brackish ocean waters along the coast of Port Nolloth and the abrasive action of wind-blown sand from the neighboring desert pose severe challenges to the durability of the equipment. The equipment to be constructed should have materials that can withstand high corrosion, erosion, and biofouling resistance, especially for ADCPs.

The equipment should be small in size so that it does not interfere much with the natural current flow and it is easy to deploy in various locations like shallow water along the shore and deep channels off the coast. Light gear is also desirable as it facilitates easier handling during deployment and recovery, especially in the rough weather along the coast of Port Nolloth. Low power consumption is also very important, especially for long-term deployment, as power supply sources can be limited in this remote coastal area.

Cost-effectiveness is also an important factor, especially in the case of large-scale measurement. High-cost instruments may be employed to decrease the number of units that may be installed, and hence the spatial coverage of the readings. A titanium alloy housing for ADCPs is a good example. Titanium alloy possesses excellent corrosion and erosion resistance in sea water and from sand grains. It is also hard and light, making it perfect for use under the harsh conditions off Port Nolloth. While being a high-performance material, advances in the manufacture of the material have made the cost of titanium alloy-cased ADCPs lower, thus making them an affordable option for large-scale monitoring of coastal currents within the area.

6. How to Choose the Right Instrument for Measuring Current?

Choosing the right instrument for measuring current in Port Nolloth is dependent on the purpose of the use.

Types of ADCPs Depending on Application

• Ship-mounted ADCP: It is the optimal instrument for making wide-scale surveys of Port Nolloth's coastal waters if mounted on a drifting vessel. As the ADCP is set while the ship moves through the waters, the instrument can continuously gather currents along its travel route and record a wide-scale overview of current regimes dominated by the Benguela Current and wind. This is used in operations such as ocean navigation, calculation of the general circulation of waters in the region, and fishery management to determine where there are abundant fish populations.
• Bottom-mounted (Sit-on-the-bottom) ADCP: Installed on the seafloor, these ADCPs are appropriate for long - term, point - specific measurements. They can remain stationary in a position for extended periods to make measurements of the currents at a specific location. This type of ADCP is beneficial when exploring the neighborhood conditions of the fine-scale dynamics of the current, for instance, how submergent underwater features affect the current flow and how regimes of currents change over time. This information is significant in ecological research, environmental monitoring, and identifying human activities impacting the marine environment.
• Buoy-mounted ADCP: Installed on a floating buoy, these ADCPs can drift with the current, measuring the velocity at different depths as they move. They are best employed to monitor large-scale, synoptic current patterns in open water distant from Port Nolloth or tracing the movement of water masses propelled by the Benguela Current over extended distances. This device can provide valuable information for predicting the dispersion of pollutants, the migration of marine life, and the health of the marine ecosystem.

Frequency Selection

The ADCP frequency must be selected with care depending on the water depth. A 600kHz ADCP is appropriate for water depths of up to approximately 70m, offering high-resolution measurements in relatively shallow waters along the Port Nolloth shoreline. For depths of approximately 110m, a 300kHz ADCP would be more appropriate, enabling the acoustic signals to penetrate further into the water column while still offering reasonable measurement accuracy. In very deep water, up to 1000m, a 75kHz ADCP is typically used, which can be used in the deeper channels off the Port Nolloth coast.

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.