1. Where is Abidjan?
Abidjan, the economic capital of Côte d'Ivoire, is well-positioned on the nation's south - central coast, embracing the Gulf of Guinea, a significant part of the tropical Atlantic Ocean. This cosmopolitan city is a vibrant blend of modernity and nature, and its coastline is a significant economic and cultural lifeline. Abidjan's coast has a highly diverse landscape of extensive sandy beaches, intricate lagoons, and a comprehensive network of canals that slice through the city.
Abidjan's diverse population is a dynamic blend of many various ethnic groups, which all contribute to its rich heritage. Fishing has been a conventional means of survival for many Abidjanais for centuries, with local fishermen relying on the rich resources of the sea. Abidjan's fish markets are thriving hubs, filled with an assortment of fresh catches ranging from tiny, highly colored reef fish to commercially significant large species. Aside from fishing, Abidjan harbor is one of West Africa's busiest ports, facilitating extensive trade in cocoa, coffee, and other goods. The port's activity has fueled the city's growth and development and makes it a major economic center for the region.
Surrounding Abidjan, the sea around it is a dynamic marine ecosystem. The warm tropical waters of the Gulf of Guinea provide a diverse range of marine organisms. Coral reefs, even with the danger from human activities, still host a range of fish, crustaceans, and other invertebrates. Large marine mammals such as dolphins and whales are also known to frequent these waters as part of their migratory routes. The seafloor topography off Abidjan is complex, with underwater ridges, canyons, and seamounts that influence the local coastal currents as well as the marine organism distribution.
2. How are the coastal currents off Abidjan?
The coastal currents off Abidjan are controlled by a combination of large-scale oceanic and local processes. The Guinea Current, a significant warm - water current moving westward along the African coast, has a significant impact on the region. The current transports warm, nutrient - rich water, which supports a healthy marine ecosystem but also impacts the direction and speed of the local coastal currents. Strength and location of the Guinea Current may also change seasonally, producing variability in salinity, water temperature, and the general current regime off Abidjan.
Seasonal wind patterns also define the coastal currents. There are strong onshore winds during wet seasons that push surface waters toward the coast. This has the potential to bring coastal upwelling in some areas, where the surface water is displaced and colder, richer water from the deeper levels ascends to the surface. Instances of upwelling are of great importance to the marine environment locally, because they fuel phytoplankton development, the base of the marine food web. Against this, during the dry season, offshore winds reinforce the current so the surface water pushes further offshore and changes both the direction of the current and the flow speed.
Abidjan's typical geography, including its canals and lagoons, also deflects the current further. Because there is contact between the sea and the lagoons, which constitutes the closely linked loop of currents. In addition, since there are rivers emptying into the sea along Abidjan, such as the Ébrié Lagoon, can dump enormous volumes of fresh water into the seawater. The fresh - water input affects the salinity and density of water and therefore the flow of the currents and makes intricate mixing patterns.
3. How to observe the coastal water flow of Abidjan?
There are multiple means of observing the coastal water current of Abidjan. Surface drifting buoy technique is a traditional means. Special buoys with GPS units are dropped on the water surface. The buoys follow the surface currents, and their path is monitored over time. By tracking where the buoys are at regular intervals, researchers can determine the direction and velocity of the currents at the surface. This method, however, only provides information on the surface currents and might not indicate the flow at any other depths.
The anchored boat method involves anchoring a boat in a single location and using current-measuring devices on board. Equipment such as electromagnetic current meters is employed from the boat to measure the water velocity at different depths. While this method can provide more accurate information about the current situation surrounding the boat, it has its limitations. The area it can cover is restricted, and the presence of the boat may disrupt the natural flow of the water, which might lead to inaccurate readings.
The Acoustic Doppler Current Profiler (ADCP) method has emerged as a more advanced and efficient tool for tracking coastal currents. ADCPs are able to measure the water velocity at different depths simultaneously, an entire picture of the water flow structure from the surface of the water to the ocean floor. This is ideal for studying the complex and dynamic coastal currents off Abidjan.
4. How do ADCPs based on the Doppler principle operate?
ADCPs are based on the Doppler principle. They emit acoustic signals into the water column. As these signals encounter suspended particles in the water, e.g., sediment, plankton, or small animals, a portion of the signal is backscattered towards the ADCP. The frequency of the backscattered signal is shifted based on the motion of the particles (and thereby the water) relative to the ADCP.
With these changes in frequency, the ADCP current profiler can calculate the speed of water at different levels. The majority of ADCPs employ a set of beams of sound, typically spread in a fan-like arrangement. Data from each of the beams is subsequently integrated and employed to determine the three-dimensional velocity vector of the water, which provides accurate information on the speed as well as the direction of flow of the current at a number of locations in the column of water. This non-invasive measurement technique allows continuous and accurate monitoring of the water flow without ever having to sample the water.
5. What does it take for high-quality measurement of Abidjan coastal currents?
For high-quality measurement of Abidjan coastal currents to be realized, certain key requirements of the measuring equipment must be met. The most critical one is reliability of the material. The coastal marine environment in the vicinity of Abidjan is harsh, with saltwater, strong currents, exposure to solar radiation, rain, and varying temperatures. The equipment must be resistant to extreme environmental conditions against corrosion, mechanical stress, and temperature.
The gear must be also compact and light. The smaller and lighter the device, the simpler it can be deployed and retracted and carried and deployed, especially in Abidjan's densely populated coastal areas. Low power consumption is also critical because it will enable longer - term deployments with little necessity to replace batteries or recharge. Cost - effectiveness is also crucial, as prolonged - scale measurement may be required to obtain detailed knowledge of complex current regimes over the region.
In the case of ADCPs, the material used to make the casing is very important. Titanium alloy is a good option for the casing. It has very good corrosion resistance, which is very important in the saltwater - rich environment of Abidjan. It has a high strength - to - weight ratio, meaning that the ADCP will be able to handle the forces of the strong coastal currents but will be relatively light to handle and deploy. Furthermore, titanium alloy has good fatigue properties, allowing the ADCP flow meter to function effectively for a long duration and provide accurate measurements.
6. How to Choose the right equipment for current measurement?
The selection of the correct equipment for current measurement in Abidjan depends on the use. For in-transit measurement on a vessel, a ship-mounted ADCP is the optimal choice. It can continuously observe the currents as the ship travels through different areas, providing real - time data on the movement of water, which is helpful for navigation, fishing, and marine commerce activities. In case long - term fixed - point observation at the ocean floor is required, a bottom - mounted ADCP is more suitable. This ADCP can be fixed on the seafloor to monitor currents for extended periods, and it is useful for underwater facility construction and ecological studies. For near-surface and upper-water-column monitoring, a buoy-mounted ADCP offers a simple solution in the sense that it can be anchored or allowed to drift with the currents, giving continuous reports of near-surface and surface current conditions.
The frequency of the ADCP profiler is also to be taken into account. A 600kHz ADCP can be utilized for water depth up to 70 meters, which is ideal for shallow waters in the coastal regions of Abidjan. A 300kHz ADCP can support depths up to 110 meters, while a 75kHz ADCP will do for greater depths, up to 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 estimate Abidjan's coastal currents?