1. Where is Cape Coast?
Cape Coast, one of Ghana's oldest cities, is located on the nation's southern shore overlooking the Gulf of Guinea, a great lake within the immense basin of the Atlantic Ocean. The charming city is renowned for its historic past, multicultural background, and picturesque seacoast. The seacoast along Cape Coast is miles long with a mixed topography of sandy shores, rock bluffs, and curving estuaries.
The city's population is a blend of various ethnic groups, each contributing to its rich cultural tapestry. Fishing has been a long-standing component of the local economy, with fishermen paddling in wooden canoes and motorized vessels into the sea. The markets selling fish locally are bustling with activity, with a variety of fresh catches such as tuna, mackerel, and shrimp which not only support the livelihood of the locals but also constitute a part of the regional cuisine. Other than fishing, Cape Coast is also famous for its history, more so the colonial castles and forts during that time, including Cape Coast Castle, which are strong reminders of the transatlantic slave trade. The sites are popular among tourists from around the world, adding a cultural and economic dimension to the city.
Sitting adjacent to Cape Coast, the waters within the surrounding regions are part of an active marine ecosystem. The warm and tropical waters of the Gulf of Guinea are a haven for abundant biodiversity. Coral reefs, although threatened by the impacts of climate change and man's activities, still provide home to a mix of colorful species of fish, mollusks, and other sea creatures. Larger marine animals like dolphins and whales are from time to time spotted as they migrate through these waters. The sea floor morphology off Cape Coast is made complex by the existence of underwater ridges, canyons, and seamounts that strongly influence the local coastal currents and affect the distribution of marine organisms.
2. What is the state of the coastal currents off Cape Coast?
The coastal currents off Cape Coast are influenced by a mix of large-scale oceanic and local conditions. The Guinea Current, a powerful warm - water current flowing west along the African coast, affects the region profoundly. The current carries warm, nutrient - rich water, which not only sustains a rich marine ecosystem but also impacts the direction and speed of the local coastal currents. Strength and position of the Guinea Current can vary seasonally, altering water temperature, salinity, as well as the overall current patterns off Cape Coast.
Seasonal wind regimes also affect coastal currents quite noticeably. Dominant strong onshore winds prevail during the wet season, pushing surface waters onto the land. This can lead to increased coastal upwelling in some areas, as the top water is forced back and cooler, nutrient-dense water from deeper depths rises to the surface. Upwelling events are important to the local marine ecosystem, as they stimulate the development of phytoplankton, the base of the marine food web. On the other hand, offshore winds prevail in the area during the dry season, pushing the surface waters away from the coast and reversing the direction and speed of the current.
The unique topography of Cape Coast with its headlands and bays also alters the flow of the currents. Water streaming along the coast collides with these landforms, which may cause separation, convergence, or instantaneous reversal of the currents. Also, where rivers which discharge to the sea along Cape Coast, such as the Ankobra River, are found, they introduce huge volumes of fresh water into the coastal water. Fresh - water input acts on the salinity as well as on the density of the water, and therefore on the motion of the currents, and creates complex mixing patterns.
3. How to observe the coastal water flow of Cape Coast?
There are several means of monitoring the coastal water current of Cape Coast. The surface drifting buoy technique is one of the ancient methods. Buoys carrying GPS tracking devices are released into the sea. The buoys are carried by the surface currents, and their trajectories are monitored over a period of time. By tracking the buoys' position at regular intervals, scientists can determine the speed and direction of the surface-level currents. But the method only provides a snapshot of the currents at the surface and may not necessarily reveal flow elsewhere.
The anchored boat method involves securing a boat to a single location and using current-measuring equipment onboard. Equipment such as electromagnetic current meters is employed from the vessel to measure the velocity of the water at different depths. Even though additional detailed information about the type of current close to the vessel can be provided through this method, it does not come without disadvantages. It is only capable of measuring over a limited area, and the vessel could disturb the natural movement of the water, thereby leading to an unrepresentative measurement.
The Acoustic Doppler Current Profiler (ADCP) method has developed into a more advanced and efficient method of quantifying coastal currents. ADCPs are able to measure the velocity of water at multiple depths simultaneously, providing an overall description of the structure of the water flow from the surface to the ocean floor. They are therefore capable of studying the intricate and dynamic coastal currents along Cape Coast.
4. How do ADCPs based on the Doppler principle operate?
ADCPs operate on the Doppler principle. They emit acoustic pulses into the water column. When they encounter particles suspended in the water, such as sediment, plankton, or small animals, some of the signal is reflected back towards the ADCP current meter. The frequency of the backscattered signal is Doppler shifted relative to the motion of the particles (and thus the water) relative to the ADCP.
On the basis of these changes in frequency, the ADCP profiler can subsequently estimate the velocity of the water at every depth. With the exception of a few, ADCPs use several sonar beams in a fan-like arrangement. These beams are subsequently averaged into the three-dimensional velocity vector for the water with exact knowledge of velocity and direction for the current across the water column. This non - intrusive measurement technique allows for continuous and accurate monitoring of the water flow without the need to physically sample the water.
5. What’s needed for high - quality measurement of Cape Coast coastal currents?
To conduct high-quality measurement of Cape Coast coastal currents, several key demands must be met by the measurement equipment. Durability of the material is of highest importance. Marine conditions near Cape Coast are harsh, including salt water, strong currents, and sunlight, rain, and varying temperatures. Equipment must be resistant to corrosion, mechanical load, and rough environmental conditions.
The equipment should also be compact and light. The lighter and more compact the device, the more easily it is transported, deployable, and recoverable, especially in the sometimes rough coastal terrain of Cape Coast. Low power consumption is essential, as it enables longer - term deployments without the need for constant battery swapping or recharging. Cost - effectiveness is also essential, as high - powered measurements on a large scale may be needed to fully understand the multi - faceted current patterns of the region.
For ADCPs, the material of the casing is perhaps the most critical factor. Titanium alloy would be a suitable option for the casing. It has better corrosion resistance, which is crucial in the saltwater - dominated Cape Coast environment. It possesses high strength - to - weight ratio, meaning that it will be strong enough to withstand the forces exerted by the strong coastal currents without being too heavy to manage and deploy. Besides, titanium alloy has good fatigue resistance, allowing the ADCP flow meter to work continuously for a long period of time and record accurate measurements.
6. How to Choose suitable equipment for current measurement?
Choosing suitable equipment for current measurement in Cape Coast is application-oriented. In the case of on-the-move measurements on board a ship, the most preferred equipment is a ship-mounted ADCP. It can keep recording the currents as the ship moves in different areas, providing real-time data on the flow of water, which is useful for navigation, fishing, and oceanographic surveys. If long - term measurements at fixed locations on the seafloor are required, a bottom-mounted ADCP is better. This type of ADCP can be installed on the ocean floor to take measurements of currents for an extended period, useful for ecological study and planning underwater construction. For surface - level and upper - water - column monitoring, a buoy - mounted ADCP offers a convenient solution, as it can be anchored or allowed to drift with the currents, providing continuous data on the surface and near - surface current conditions.
The ADCP frequency is also another factor to look into. A 600kHz ADCP is suitable for up to 70 meters depth and would be perfectly suitable for shallow coastal waters near Cape Coast. A 300kHz ADCP can be used for up to 110 meters, while a 75kHz ADCP can be used for deeper waters, 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 keep an eye on Cape Coast's coastal currents?