How do we go about measuring Maydh's coastal currents?

1. Where is Maydh?

Maydh is a coastal city in the northwestern part of Somalia. It lies facing the Gulf of Aden, the most important maritime region with a wide range of interconnections.

The surroundings of Maydh have a very variable coastline. The sandy beaches run up to meet the warm waters of the Gulf of Aden. Salinity is known to be comparatively high in the sea here, with various types of marine life abounding. The colorfulness of fish species and varieties of shellfish are so rich that they give great variety to the marine ecosystem. In the coastal areas, the presence of small rocky outcrops and little inlets adds to the geographical complexity.

From the human perspective, the sea has been part of the local community in Maydh for a long period. Fishing is a significant part of their livelihood, and the town has seen generations of maritime activities. The sea forms part of the cultural heritage of the place, represented by the traditional fishing practices and stories passed down through the years.

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

The coastal currents near Maydh are determined by several factors. First, the large-scale ocean circulation patterns in the Gulf of Aden and its connection to the broader Indian Ocean play a crucial role. The inflow and outflow of water masses between these larger bodies of water determine the general direction and strength of the local currents.

Other important influences are tidal forces. The regular rise and fall of the tides account for variations in speed and direction of the coastal currents. In places, the movement of water at high tide might be stronger, while at low tide, the flow patterns change accordingly.

All those things and more depend on wind patterns in the case of coastal currents. For example, seasonal winds may have monsoon characteristics and advance the surface waters and, thus, shift current directions. In the case of bottom topography close to the Maydh coast, a number of seafloor features-ridges, canyons, and shoals-can, by their form, divert and/or disrupt flows, creating an extraordinary complexity of local flow features along the shore.

3. How would one observe Maydh coastal water flow?

• Surface Drift Buoy Method: This is done by deploying buoys on the water surface, which are designed to drift with the currents. Through tracking these buoys, usually via satellite or other positioning systems, information on the direction and speed of the surface currents can be derived. This method mainly deals with the surface layer and does not give the overall view of the currents at different depths.
• Anchor Boat Method: Under this, a boat is anchored at some place in the water of the sea coast. After that, instruments are used to measure the flow of water at different depths around the boat. This will be able to provide more comprehensive information about the area around the vessel than is usually derived from surface drift buoy, but this can be limiting over larger areas, besides the impact of the movements of the boat itself through wave and other turbulence effects.
• Acoustic Doppler Current Profiler (ADCP) Method: ADCP current meter is an advanced, much handier method for current measurements. It uses sound waves to measure the velocity of water at multiple depths simultaneously. It can be deployed in different ways: on boats, on the seabed in a fixed position, or attached to buoys. Thanks to its ability to provide detailed and continuous data on current profiles from the surface down to significant depths, it has become a preferred choice for observing the coastal currents near Maydh.

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

ADCPs work with the principle of the Doppler effect. They send out sound pulses into the water at a known frequency. These sound waves are changed in frequency by the Doppler effect while encountering moving particles in the water, such as suspended sediment or small organisms. The shift in frequency is proportional to the velocity of the water carrying those particles.

The ADCPs measure the frequency shift of the reflected sound waves from different directions and at different depths and calculate the multi-dimensional-regularly horizontal and vertical-velocity components of the water flow. Usually, multiple acoustic beams are used in an ADCP current profiler in order to obtain a more comprehensive understanding of the current structure. This enables the development of detailed current profiles that indicate precisely how the water is moving at different depths along the Maydh coast.

5. What is required for good quality measurement of Maydh coastal currents?

Given characteristic the equipment should have for high-quality measurement of coastal currents near Maydh, includes having reliable material in order to stand up to harsh marine conditions. It should be of salt-water resistant material put under mechanical tension due to waves, extreme variations in temperature.

Devices must have a compact form to enable rapid deployment and mounting in all terrains, from boats to ocean beds to buoys. This light design enables good maneuverability and handling. It must be of low power so that all devices can remain on for very long times using minimal battery replacement or large supplies of power. It is cheap, hence allows for more applications and large-scale measurements.

The casing of the ADCPs includes a very good choice of Titanium alloy. The Titanium alloy material is of high strength and, hence can support the mechanical forces in the marine environment. It has a high resistance to corrosion by seawater and therefore largely prolongs the life of the equipment. It has a relatively low density compared to some other metals, making it suitable for applications where weight is a concern, which is in good agreement with the requirements for coastal current measurement devices near Maydh.

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

Based on the Use Purpose

• Shipborne ADCP: This is suitable when the measurement needs to be done while the ship is in motion. It can provide continuous data on the currents as the ship navigates along the coast-for example, during scientific research voyages or routine monitoring by naval or research vessels.
• Bottom-mounted ADCP: Very good for long-term and stable measurements at a fixed location on the seabed. It gives detailed information on the current patterns in a specific area over an extended period, which is useful for understanding the local hydrodynamic conditions.
• ADCP mounted on buoy: This will be highly suitable for the surface and near-surface current measurements when the buoy is deployed in the coastal waters. It shall help in the study of the interaction of the atmosphere with the ocean surface currents.

Based on different frequencies

• In general, a frequency of 600 kHz works quite well for ADCPs where water depths in relatively shallow coastal waters do not exceed 70 m; current can be measured well in this depth range with good accuracy.
• When working in waters of 70 to 110 meters, the 300 kHz ADCP would be more suitable as it can effectively penetrate the water column for the capture of reliable data at those depths.
• When the water depth is up to 1000 meters, as in some of the deeper parts of the Gulf of Aden around Maydh, the most appropriate choice to measure the currents throughout the water column would be a 75 kHz ADCP.
• There are several famous brands on the market for ADCPs, such as Teledyne RDI, Nortek, and Sontek. If you want to find a good-quality but economic one, you can go for the China Sonar PandaADCP. This ADCP is made of all-titanium alloy material, so it is durable and resistant in the marine environment. In addition, this model boasts a very impressive cost-performance ratio. You can learn more about it from its official website: https://china-sonar.com/.

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