1. Where is Lomé?
Lomé, the vibrant capital of Togo, is situated on the nation's southwestern coastline, gracefully embracing the Gulf of Guinea, a significant body of water in the expanse of the Atlantic Ocean. This maritime city is an intriguing amalgam of nature and city, with its coast line being an essential bridge between land and sea. The coast line of Lomé stretches miles long, constituting a rich mosaic of sandy coasts, serpentine estuaries, and active port installations.
Its population is a rich mosaic of various ethnic communities, each contributing its own individual contribution to the city's own cultural heritage. Fishing has been a part of the economy for decades, with fishermen embarking in their wooden boats early in the morning to collect the bountiful harvest of the sea. The local fish markets are bustling places of activity, filled with an assortment of fresh catches, from succulent shrimps to large, multicolored fish. Apart from fishing, Lomé has also emerged as a major economic and transport center, with its new port offering trade not just within Togo but with other countries of the world. The port has a constant flow of cargo vessels, tankers, and passenger ships, making it a key node in the regional maritime trade network.
The waters around, surrounding Lomé, are within a rich and diverse marine ecosystem. The Gulf of Guinea's warm tropical waters support great biodiversity, with coral reefs providing habitats for countless species of fish, mollusks, and other marine organisms. The reefs are an underwater kaleidoscope of life and colors. Large sea mammals like dolphins and whales also make occasional appearances along their migratory routes. The seafloor morphology off Lomé is complex, involving seamounts, underwater ridges, and canyons that have a strong impact on the distribution of the marine fauna and are of great significance in controlling the local coastal currents.
2. What is the situation regarding the coastal currents off Lomé?
The coastal currents off Lomé are governed by a combination of large - scale oceanic and local processes. The Guinea Current, a powerful warm - water current flowing west down the coast of Africa, plays a major role in the region. The current flows warm, nutrient - rich water, which not only keeps the marine ecosystem healthy but also has an effect on the direction and speed of the local coastal currents. The strength and position of the Guinea Current seasonally vary, which alters the water temperature, salinity, and overall current regime off the coast of Lomé.
Wind regimes during the seasons also play an important role in the coastal currents. There are intense onshore winds in the wet season that push the surface waters ashore. This can lead to upwelling along the coast in some areas due to displacement of surface water and replacement with colder more nutrient-laden water from deeper depths approaching the surface. Upwelling events are critical to the in-place marine ecosystem since they trigger marine phytoplankton development and they help to supply the foundation of the ocean food chain. On the other hand, during the dry season, offshore winds dominate, and the surface waters are driven away from the coast, altering the direction and velocity of the currents.
The shape of the Lomé coastline, its bays, inlets, and headlands, also alters the flow of the currents. When water moves along the coast, it encounters these landforms, which can cause the currents to bifurcate, converge, or turn sharply. Moreover, the presence of rivers that empty into the sea near Lomé, such as the Mono River, will add massive amounts of fresh water to the sea water. The fresh - water addition affects the salinity and density of the water and therefore the movement of the currents and creating complex mixing patterns.
3. How to observe the coastal water flow of Lomé?
There are several means of observing the coastal water current of Lomé. The surface drifting buoy method is one of the earlier methods. GPS tracking devices are mounted on special buoys that are dropped into the ocean. The buoys float on the surface currents, and their paths over time are followed. By tracking the location of the buoys at regular intervals, scientists are able to quantify the direction and speed of the surface-level currents. This method, however, provides information regarding the currents at near - surface levels and may not indicate the flow at deeper levels.
The anchored boat method involves mooring a boat in a fixed location and using current-measuring tools onboard. Tools like electromagnetic current meters are released from the boat to take the velocity of water at various levels. Although with this technique one can get more precise information on the current nature in the near vicinity of the boat, the technique is not without its weaknesses. The covered area is limited, and there is a likelihood that the flow of water in its natural pattern will be destroyed by the existence of the boat, thus bringing about incorrect reading.
The Acoustic Doppler Current Profiler (ADCP) method is increasingly becoming a more sophisticated and advanced technique in the measurement of coastal currents. ADCPs are able to measure water velocity at more than one depth at the same time, providing a comprehensive record of the pattern of water flow from surface to seafloor. This makes them optimally prepared for the study of the complex and dynamic coastal currents off Lomé.
4. How do ADCPs based on the Doppler principle operate?
ADCPs operate on the Doppler principle. They transmit acoustic pulses into the water column. When these pulses encounter suspended particles in the water, e.g., sediment, plankton, or small organisms, a portion of the pulse is bounced back to the ADCP. The frequency of the returned pulse varies depending on the motion of the particles (and thus the water) relative to the ADCP.
Through these changes in frequency, the ADCP meter is able to compute the velocity of the water at various depths. The majority of ADCPs employ multiple sound beams, which are usually positioned in a fan-like pattern. The results from each beam are subsequently averaged to compute the three-dimensional velocity vector of the water and give precise data on both speed and direction of the current at various locations in the water column. This non - intrusive measurement method enables continuous and precise monitoring of the water flow without physically sampling the water.
5. What's required for high - quality measurement of Lomé coastal currents?
For the proper measurement of coastal currents in Lomé, there are several essential requirements to be met in the measuring equipment. Material reliability is most significant. The environment of the sea surrounding Lomé is extremely harsh with saltwater, strong currents, and exposure to sun, rain, and fluctuating temperatures. The equipment must be resistant to corrosion, able to withstand mechanical stress, and harsh environmental conditions.
The instrument also needs to be light and small. A lighter and more compact unit is easier to carry, deploy, and recover, especially in the often hard - to - reach coastal areas of Lomé. Low power consumption is critical as it enables longer - term deployments with little battery replacement or recharging. Cost - effectiveness is also a key consideration because prolonged measurements may be required in an effort to fully understand the complex current patterns within the region.
In working with ADCPs, material for the casing is an extremely significant factor. A titanium alloy casing is an excellent choice. It offers excellent corrosion resistance, which is critical in Lomé's saltwater - dominated environment. Its high strength - to - weight ratio allows it to be strong enough to withstand the forces exerted upon it by the powerful coastal current but light enough to be handled and deployed with ease. Moreover, titanium alloy is fatigue-resistant, and the ADCP profiler can be employed for long periods of time without any loss of measurement accuracy.
6. How to Choose the appropriate equipment for current measurement?
The choice of the appropriate equipment for current measurement in Lomé is application-dependent. For shipborne moving measurements, a ship-mounted ADCP is the most suitable. It can continuously measure the currents as the ship moves from one region to another, providing real-time data on the water flow, which is crucial in navigation, fishing, and maritime trading activities. If long-term, fixed-point measurements at the sea bottom are required, a bottom-mounted ADCP is preferred. Such an ADCP can be fixed to the seabed and used to observe currents for a long period of time, which has application in ecological surveys and planning of underwater structures. For surface monitoring and upper - water - column monitoring, the convenient solution for a buoy - mounted ADCP is that it can be either anchored or float with the current, giving permanent data on surface and near - surface current regimes.
The ADCP current profiler frequency must also be taken into account. An ADCP of 600kHz can operate in waters as deep as 70 meters, making it safe for the shallow coastal waters surrounding Lomé. An ADCP of 300kHz would work at depths as great as 110 meters, while an ADCP of 75kHz would work for deep waters, up to a depth of 1000 meters.
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.
How do we quantify the coastal currents of Lomé?