1. Where is Lagos?
Lagos, the economic and cultural hub of Nigeria, is strategically located on Nigeria's southwest coast along the extensive Bight of Benin, a large section of the Gulf of Guinea in the Atlantic Ocean. This bustling megacity is a fascinating blend of modern glass skyscrapers, historic bazaars, and vibrant coastal biodiversity. Lagos' shoreline stretches miles long, with a varied landscape of sandy shores, creeks fringed with mangroves, and port areas.
The city's population is a cosmopolitan mix of various ethnic groups, all contributing to the rich cultural tapestry. Fishing has long been one of the prime sources of livelihood for most Lagosians, with local fishermen venturing into the sea every day to come back with a bountiful catch of fish, shrimp, and other seafood. These fresh materials are then hawked at the colorful local markets, which constitute the backbone of the city's economy. In addition to this, Lagos has also developed into a principal economic force, with its harbors allowing wide-ranging trade not only within Nigeria but also in the international marketplace. The waterborne activities within Lagos are not only fishing and commerce but also oil and gas exploration, underscoring still further the intense relationship Lagos shares with the ocean.
Near Lagos, the body of water adjacent to it lies within a dynamic and productive sea ecosystem. The warm, tropical waters of the Bight of Benin are home to a rich marine fauna. Coral reefs, although threatened by the perils of overfishing and pollution, but still support thousands of species of bright-colored fish, mollusks, and other invertebrates. Dolphins, and whales also make occasional appearances on their transit through these seas in their migratory routes. The ocean topography surrounding Lagos consists of shallow continental shelves, deep channels, and seamount ridges that are all of special significance in shaping the coastal currents close to the vicinity of Lagos and influencing the marine animals' distribution.
2. How is the health of the coastal currents around Lagos?
The coastal currents around Lagos are determined by both large - scale oceanic and local conditions. The Guinea Current, a powerful warm - water current running westward along the coast of Africa, is significant in the region. The current carries warm, nutrient - rich waters, which not only sustain a healthy marine ecosystem but also affect the direction and speed of the local coastal currents. Strength and position of the Guinea Current also vary seasonally, producing fluctuation in water temperature, salinity, and overall pattern of currents near Lagos.
Coastal current condition is also affected by seasonal wind patterns. Wet season is characterized by dominant onshore winds over the region, pushing surface waters onshore. This can lead to increased coastal upwelling in certain areas, as the top water is forced out of the way and colder, nutrient-filled water from below rises to the surface. Upwelling events are essential to the local marine food web, as they encourage the proliferation of phytoplankton, the base of the marine food web. On the contrary, during the dry season, offshore winds dominate, driving the surface waters out to sea and reversing the direction and velocity of the currents.
The unique Lagos topography with numerous bays, inlets, and headlands also influences the flow of the currents. When water flows along the shore, it encounters these land features, which might cause the currents to bifurcate, converge, or abruptly change direction. Moreover, the influx of rivers like the Ogun and Lagos rivers, which flow into the sea close to the city, adds massive amounts of fresh water to the coastal waters. This fresh-water input impacts the salinity and density of the water and hence the flow of the currents and produces intricate mixing patterns.
3. How to observe the coastal water flow of Lagos?
There are several methods through which observation of the Lagos coastal water drift can be achieved. The surface drifting buoy method is a traditional technique. GPS tracking units are mounted on specially designed buoys that are released onto the water. The buoys get drifted by the surface currents, and their path is monitored over time. By tracking the location of the buoys at regular intervals, scientists can determine the direction and speed of the surface-level currents. But this method will only provide information on the currents near the surface of the water and may be a bad indication of the flow elsewhere.
The anchored boat method is where a boat is anchored at a location and current-measuring gear on board is used. Probes such as electromagnetic current meters are released from the boat to measure the velocity of the water at different depths. While this technique might provide more detailed information regarding the current conditions near the boat, it is not without its shortcomings. The area covered is small, and the boat can interfere with the natural flow of the water, which could lead to inaccurate readings.
The Acoustic Doppler Current Profiler (ADCP) method has been found to be a more advanced and efficient method of coastal current measurement. ADCPs are capable of measuring the water velocity at multiple depths simultaneously, providing an exhaustive description of the water flow structure from the surface to the bottom. Therefore, they are optimally suited to study the complex and dynamic Lagos coastal currents.
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 particles suspended in water, such as sediment, plankton, or small animals, some component of the pulse is reflected back to the ADCP. The frequency of the reflected pulse is altered depending on the motion of the particles (and thus the water) relative to the ADCP.
By studying these frequency alterations, the ADCP current profiler can determine the water's speed at different levels. Most ADCPs function with a set of acoustic beams, typically in fan - like formation. Information from each beam is utilized to calculate the three - dimensional velocity vector of water, and from this, accurate information on speed and direction of the current is found at different locations within the water column. This non-invasive measurement technique allows continuous and accurate measurement of the water flow without the need to physically sample the water.
5. What is needed for high-quality measurement of Lagos coastal currents?
In precise measurement of Lagos coastal currents, some essential conditions must be met in the measurement equipment. Priority must be accorded to material stability. The marine environment near Lagos is turbulent and consists of saltwater, strong currents, and direct sun radiation, rain, and alternating temperatures. Corrosion, mechanical stress, and extreme weather conditions must not harm the equipment.
The equipment must also be small and portable. A light and smaller instrument is easier to transport, deploy, and recover, especially in the congested and generally cluttered waters of Lagos. Low power use is critical, as it provides for longer - term deployments without the need for continual replacement or recharge of batteries. Cost - effectiveness is also crucial, as large - scale measurements may be required to achieve a solid understanding of the complex current patterns of the region.
With regards to ADCPs, the casing material is most critical. The ideal material for the casing is titanium alloy. It possesses great corrosion resistance, which is highly desirable in Lagos' saltwater-saturated environment. It has a high strength-to-weight ratio, which enables the ADCP to be exposed to the forces of the strong coastal currents without compromising much strength while being relatively light and easy to handle and deploy. Also, titanium alloy has good fatigue life, allowing the ADCP flow meter to work effectively for extended periods and provide correct readings.
6. How to choose the proper equipment for current measurement?
The equipment to be used for current measurement in Lagos is dependent on the application intended. For ship-based moving measurements, a ship-mounted ADCP would be ideal. It can continuously monitor the currents as the vessel travels across various regions, offering real - time information regarding the flow of water, which is useful for navigation, fishing, and maritime operations. For long - term, fixed - point measurements at the ocean floor, a bottom - mounted ADCP is preferable. This ADCP can be fixed on the seafloor to measure currents over a long term, which is used in ecological surveys and infrastructure planning. For shallow - water and upper - water - column observing, a buoy - mounted ADCP provides a useful solution because it can be moored or permitted to drift with the currents, giving continuous information on the surface and near - surface current situation.
Frequency of the ADCP is another crucial aspect. The 600kHz ADCP would be suitable for up to 70 meters depth water and suitable for shallow waters along the coastal region close to Lagos. 300kHz ADCP would be used for water depths up to 110 meters, while the 75kHz ADCP can be used in deeper water up to 1000 meters.
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.
How do we gauge Lagos coastal currents?