How do we measure the coastal currents at Port Harcourt?

1. Where is Port Harcourt?

Port Harcourt, a city of high density in southern Nigeria, is located on the Bonny River, which flows into the vast Gulf of Guinea, an arm of the Atlantic Ocean. The metropolis, whose busy streets bustle with energy, is nicknamed the oil capital of Nigeria, but its attractiveness extends far beyond its economic stature. Port Harcourt's location in the middle of the Niger Delta offers a varied and unique coastal environment with complex blending of mangrove swamps, waterways, and sandy beaches.

Port Harcourt is located within one of the largest river deltas in the world, the Niger Delta. It is a muddled array of tributaries, estuaries, and creeks that make up a dense and continuously shifting ecosystem. The mangrove ecosystem along the water courses is not just a lifesaver of millions of flora and fauna but also a natural sea defense barrier to protect against coastline erosion. Mangroves provide habitats for birds, fish, and crustaceans and maintain local biodiversity.

Port Harcourt is home to a multi-heterogeneity of ethnic communities with each of them having their own custom, language, and culture in the city. Fishery and agriculture have also been dominant survival activities in the area since time immemorial, with rich waters along the Bonny River and Gulf of Guinea returning very profitable catches of fish and other sea products. Fresh catches abound in the markets, bearing testament to the intimate association of people with the sea. Apart from its historical economy, Port Harcourt has experienced immense growth and development in recent decades, spearheaded by the oil and gas sector, making the city a leading economic hub in West Africa.

2. What are the coastal currents off Port Harcourt?

The coastal currents off Port Harcourt are dominated by a combination of the large - scale oceanic and local processes. The Guinea Current, also a major warm-water current system of Africa flowing westward along the coast of Africa, is reported to have a major influence on the area. The current carries warm, nutrient-rich waters into the Gulf of Guinea, which also affects the temperature, salinity, and general ecological balance of water around Port Harcourt. The position and strength of the Guinea Current fluctuate seasonally and bring changes in the direction of the coastal currents.

The coastal currents also have a big influence from the seasonal winds. During rain, onshore winds prevail during the wet season, and surface water is driven shoreward. This leads to increased coastal upwelling at some locations, as surface water is pushed outward and substituted by cold, nutrient-dense water from deeper waters. Upwelling events are crucial to the native marine ecosystem because they sustain phytoplankton growth, which forms the basis of the food web. On the other hand, in the dry season, the coastal winds dominate and the surface water is blown off the coast, reversing the direction and speed of the current.

The Niger Delta's complex topography, with innumerable rivers, creeks, and estuaries, also makes the coastal current complex. The influx of the fresh water from the rivers, like the Niger River, reduces the salinity of the sea water and affects the density and flow of the masses of water. The blending of the salt water and the fresh water creates a dynamic mixing zone, which may lead to the generation of the independent structures of the current and eddies. Besides, the headland and bay topography of the coastline could cause the currents to diverge, converge, and reverse, further complicating the coastal current system.

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

There are different methods for observing the coastal water flow of Port Harcourt. The surface drifting buoy method is a traditional one. Special buoys, which have GPS tracking devices installed in them, are released in water. Surface currents move the buoys, and gradually the path of these buoys is monitored. By tracking the position of buoys at regular intervals of time, the direction and velocity of the surface-level currents are calculated. But this method only provides data for currents in the water at the surface and may not indicate the flow at lower levels.

The boat anchored method involves holding a boat in a fixed position and using current-measuring equipment on board. Devices such as electromagnetic current meters are dropped into the water from the boat to gauge the speed of the water at different depths. Although this method can provide more accurate information on the features present in the area surrounding the boat, it is not without its limitations. The area that it can survey is restricted, and the presence of the boat may disrupt the natural flow of the water, which can result in inaccurate measurements.

The Acoustic Doppler Current Profiler (ADCP) method has also arrived as an advanced and efficient coastal current measurement. ADCPs can simultaneously measure water velocity at many depths, thereby giving a vivid picture of the flow structure of water from the surface to the sea bed. They are thus optimally appropriate for studying the variable and complex coastal current in Port Harcourt waters.

4. How do ADCPs based on the Doppler principle operate?

ADCPs operate on the Doppler principle. They send out acoustic pulses into the water column. When these pulses encounter suspended matter in the water, i.e., sediment, plankton, or tiny animals, a portion of the pulse is reflected back to the ADCP. The frequency of the back-scattered signal is shifted depending upon the motion of the particles (and thus the water) relative to the ADCP.

By analyzing these changes in frequency, the ADCP can calculate the water's velocity at different depths. Most ADCPs use multiple acoustic beams, usually in a fan - shaped configuration. Data from each beam is then combined to determine the three - dimensional water velocity vector, providing accurate information about both the speed and direction of the current at many points in the water column. This non-destructive measurement technique allows continuous and accurate monitoring of the water flow without physically sampling the water.

5. What are the requirements for high-quality measurement of Port Harcourt coastal currents?

For high-quality measurement of Port Harcourt coastal currents, certain basic requirements must be met by the measuring equipment. Material reliability comes first. The marine environment around Port Harcourt is harsh, consisting of saltwater, strong currents, and exposure to the elements. The equipment must be corrosion- and strain-resistant, as well as withstand extreme changes in temperature.

The equipment needs to be compact and lightweight. A smaller and lighter device is easier to deploy, especially in the heavily populated and often difficult - to - reach coastal areas of the Niger Delta. Low power consumption is also valuable, since longer - term deployments can be accomplished without having to constantly replace or recharge batteries. Also, cost - effectiveness is necessary, as bulk measurements may be needed to ensure a full realization of the complex current patterns of the region.

When it comes to ADCPs, the material of the casing matters a great deal. Titanium alloy is one of the best materials for a casing. This possesses superb corrosion resistance, and this is absolutely crucial in the saline - dominated environment of Port Harcourt. Its strength - to - weight ratio is high enough that the ADCP can withstand the forces exerted by the strong coastal currents without being unbearably cumbersome and difficult to manipulate and deploy. Furthermore, titanium alloy possesses superior fatigue properties so the ADCP will give reliable performance over the long periods and deliver accurate measurements.

6. How to Select correct equipment for current measurement?

The appropriate device for Port Harcourt current measurement depends on the application. For the movement of measurements on a ship, a ship-mounted ADCP is optimum. It can continuously measure the currents as the ship travels from one region to another and provide real-time data on the water movement, which is necessary for fishing, navigation, and oil and gas exploration. If long - term, fixed - point measurements at the ocean floor need to be taken, a bottom - mounted ADCP is to be used. This ADCP can be lowered to the seafloor to measure currents over an extended period, which is useful in environmental monitoring and infrastructure planning. For surface - level and upper - water - column monitoring, an anchored or drifting buoy - mounted ADCP is a handy option as it may be anchored or allowed to follow the current, providing continuous information on near - surface and surface current conditions.

Frequency of ADCP is also to be considered. A 600kHz ADCP would be optimum for water depth of up to 70 meters, so would be optimum for shallow coastal water off Port Harcourt. A 300kHz ADCP would be adequate for depths of up to 110 meters. A 75kHz ADCP would be optimum for deeper waters, up to 1000 meters.

There are certain well-known well - established brands of ADCPs available in the market, e.g., Teledyne RDI, Nortek, and Sontek. But for those seeking cost - effective options, the ADCP supplier China Sonar's PandaADCP is the way to go. It's constructed from pure titanium alloy, and its performance is top - notch at an affordable price. It is the ideal choice for users seeking budget - friendly ADCPs without sacrificing coastal current measurement quality. For more details, visit their website: https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and models.