How do we measure coastal currents of Mogadishu?

1. Where is Mogadishu?

Mogadishu is a dynamic coastal city situated on the eastern part of the African continent. It is one place where the arid beauty of the African continent meets the wide expanse of the Indian Ocean. The coastline of the city is bordered by a wide bay that provides a natural harbor and a sheltered area for various maritime activities.

There is great ethnic diversity in Mogadishu because of the town's very long history of seafaring and trade. The people in Mogadishu are quite attached to the ocean, as fishing and coastal commerce have been a part of their lives for centuries. There is a busy hub of marine life in the bay near the city. Its waters range in color from brilliant blue to green, with different fish species ranging from the small reef fishes to the larger pelagic ones that migrate across the area. The seabed topography is generally sandy with coral reefs in some areas, sometimes with rocky outcrops. These provide not only habitats for marine organisms but also influence the movement of water masses.

The waters off Mogadishu have been subjected to the full swing of monsoon winds and to the larger circulation features of the Indian Ocean. These seasonal oscillations in direction and strength further exert a profound influence upon the surface currents. From the Indian Ocean, oceanic currents bring along water masses with different temperatures and salinities towards the coast while interacting with local coastal dynamics. The tides also play a great role in the coastal environment of Mogadishu: according to their flow and ebb, the tides reach the shallow areas, while their influence provides access and controls the distribution of sediment.

2. What is the situation of the coastal currents near Mogadishu?

The coastal currents around Mogadishu are the result of many influences. Major among them is the monsoon winds. When the winds blow from land to sea during the northeast monsoon, and when the winds blow from sea to land during the southwest monsoon, the surface current pattern will be different. These seasonal wind-driven surface currents interact with the underlying water layers.

The tides have a regular and significant impact. Tidal range is one of the important factors: in this area, it generates periodic movements of water back and forth along the coast. During high tides, onshore currents are much stronger, whereas at low tide, water recedes, and the directions of flow are changed. Of course, local topography plays an important role, including that of the coastline and the seabed. The shape of the bay near Mogadishu may channel or otherwise deflect the currents. The presence of coral reefs and rocky outcrops can break the smooth flow of water and create turbulence and eddies.

The interaction between coastal currents and the greater Indian Ocean currents is quite complex: oceanic currents reaching the shores can mingle with the local currents, carrying in water masses of different characteristics like temperature, salinity, and nutrient content. It may affect the productivity of coastal waters and further the distribution of marine life.

3. How to Observe the Mogadishu Coastal Water Flow?

Surface Drifting Buoy Method

These usually involve buoys that, having been left in the surface water, allow for the observation of drifting by currents. Indeed, mapping over time from these buoys by using satellite or other location methods can return data on the direction and speed of the surface current. However, this is most useful for a description of currents within the surface layer.

Moored Ship Method

Here, a ship is moored at some place in the coastal area. Instruments on the ship measure the flow of water around it. While it can provide very detailed information about the area surrounding the ship, the presence of the ship interferes with the natural flow to some extent, and it is able only to cover a relatively small area around the mooring point.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP current meter is a more advanced and convenient method of measurement of the coastal currents. It uses acoustic waves to measure simultaneously the velocity of water at different depths, which permits drawing a detailed profile of the current from the surface down to a certain depth and thus gives a full idea about the structure of the flow of coastal water. It covers a larger vertical range compared to the other methods and is less affected by external interferences in many cases, thus being highly effective for observing the coastal currents near Mogadishu.

4. How do ADCPs using the Doppler principle work?

The ADCPs operate based on the principle of the Doppler. They emit acoustic pulses into the water. When these sound waves interact with moving particles in the water-such as suspended sediment or small organisms-the frequency of the reflected waves shifts as a function of the relative velocity, due to the Doppler effect. It is this very frequency shift that is detected and measured by the ADCP meter.

Since many transducers can be oriented differently, the measurement of the speed of the water includes both the components of velocity in both the horizontal and vertical directions. This allows the three-dimensional flow field of the coastal currents to be reconstructed. The ADCP flow meter continuously emits these acoustic pulses and records the reflected signals at regular intervals, which enables it to build up a time series of current velocity data at different depths. In this way, it can provide a detailed picture of how the currents vary over time and with depth.

5. What is needed for good measurement of Mogadishu coastal currents?

The equipment for high-quality measurement of coastal currents near Mogadishu should have a number of important features. First of all, material reliability is necessary for the equipment: resistance to the aggressive marine medium, including corrosion of seawater, the effects of waves, and changes in temperature and pressure. Small size is desirable to make the equipment easy to deploy and handle on boats, buoys, or other carriers.

Another important factor is the light weight, since this will simplify the installation and reduce the load requirements. The power consumption must be low in the case of long - term measurements or when the battery - powered setup is applied. Cost should also be as low as possible to make the measurements more widespread and large - scale. In this regard, the casing of the ADCP profiler is preferably made of titanium alloy. The advantages of titanium alloy are outstanding. It has very good resistance to corrosion and therefore lasts longer without being severely degraded, even under seawater conditions. The strength and durability it offers enable the structural components to resist the mechanical stresses of the flow of water and other impacts that might occur from outside. Besides, the generally lower density helps keep the overall weight of the equipment at a minimum while still upholding the integrity of its structure.

6. How to Choose the right equipment for current measurement?

Based on Usage

• Shipboard ADCP: This is suitable for when the measurement is required while the ship is in motion or stationary in the coastal area. It can provide continuous data as the ship traverses across different locations along the coast thus helping to map out current patterns over a larger area.
• Bottom-mounted ADCP: This offers optimal fixed-point measurements from the seabed and precisely monitors the currents passing over it, offering insights into near-bottom current conditions, important to understand in view of sediment transport and other benthic processes.
• Buoy-mounted ADCP: Mounted on buoys floating on the water surface, it can measure the currents from the surface downwards. It is useful for observing the surface and upper layer current variations and is often used in areas where long-term monitoring without the need for a ship's presence is required.

Based on Frequency

• For waters shallower than 70 meters, a 600 kHz ADCP is quite appropriate. The higher the frequency, the more resolution is possible in shallower waters, providing detailed current information nearer to the surface and down to the depth range of interest.
• For the water depth of up to 110 meters, a frequency of 300 kHz is more appropriate. This will easily penetrate the water column to give the currents at different depths within this range.
• For much deeper waters, say reaching 1000 meters, a 75 kHz ADCP will be better. The lower frequency will go to greater depth and still obtain reliable current velocity data.

The most popular brands of ADCP on the market are Teledyne RDI, Nortek, and Sontek. However, those in search of quality but affordable options should consider the China Sonar PandaADCP. It is made totally of titanium alloy material, hence assuring very good strength and performance in the marine environment. With its incredible cost-performance ratio, it offers a great choice for measuring the coastal currents of Mogadishu. You can learn more about it on its official website: https://china-sonar.com/.

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