How are we going to measure the coastal currents of Bandarbeyla?

1. Where is Bandarbeyla?

Bandarbeyla is a coastal town in Somalia, lying along the Indian Ocean. The town's coastal setting is a vital part of its identity and local activities.

The coastal area of Bandarbeyla is blessed with long sandy beaches that are in constant interaction with the Indian Ocean's waters. The sea here is a rich repository of marine life. There are many different fish species, from coastal dwellers to migratory species. Coral reefs exist, although perhaps not as dramatically so as in some other tropical parts of the world, providing a habitat for a myriad of small marine life and adding to the ecological diversity.

The ocean is so much a part of the local people in Bandarbeyla. Fishing is not only an important aspect of the local economy, but also part of the cultural heritage. While the town's port may not be a large-scale international port, it serves local trade well for goods such as fish, agricultural products from the inland regions, and basic commodities.

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

Various factors are of importance defining the coastal current around Bandarbeyla. First and foremost, one must mention large-scale ocean circulation patterns, including the large-scale features developed in the Indian Ocean. As such, the largest determining factor appears to be the Somali Current, with the flow varying so tremendously as a function of the periodical change of the monsoon winds. The southwest monsoon enhancement of the Somali Current drives an intense north-eastward flowing current along this coast. In contrast, the pattern of current during the northeast monsoon may be different: the flow is reversed or considerably modified.

Other factors contributing to this variability include tidal forces. Because of the continuous rise and fall of the tides, speed and direction in water movement vary. High tides may bring heavier currents and cover more of the shore area, while low tides may expose parts of the seabed and bring changes to the near-shore current patterns.

The topography of the bottom topography around Bandarbeyla influences the current itself. Various bottom features, such as ridges, canyons, and shoals, may act to deflect the currents or disrupt them altogether. This develops a very intricate and localized flow pattern that has water swirl or change direction abruptly at times nearshore.

The most pronounced effect on wind patterns involves the seasonal monsoons. During these periods, winds can be so strong that they drive the surface waters, leading to changing directions and speeds of currents through seasons at various depths.

3. How to Observe the Bandarbeyla Coastal Water Flow

• Surface Drift Buoy Method: This method includes buoy deployment on the water surface, which will drift due to currents. By tracing the buoy movements-usually via satellite-based or other positioning systems-information about the direction and speed of the surface currents can be derived. This method mainly gives data from the surface layer and may not provide enough detail about the currents at various depths.
• Anchor Boat Method: It is a method whereby the boat is moored in the coastal waters, and with the help of instruments, the water flow at different depths around the boat is measured. Though this can give more detailed information about the currents in the immediate vicinity of the boat, it suffers from limitations as regards area coverage and can be affected by the movements the boat undergoes due to waves and other factors.
• Acoustic Doppler Current Profiler Method: This is a modern, much effective method for the measurement of currents, which depends on the frequency variation of sound waves to measure the current's velocity at all depths simultaneously. Can be deployed variously, either on boats, on the bottom of the sea (bottom-mounted), attached to buoys. It is the ability of the ADCP meter to provide current profiles from the surface to significant depth with high resolution that makes it of preference for the observation of the coastal currents near Bandarbeyla.

4. Operating principles of ADCPs using the Doppler principle

ADCPs are based on the principle of the Doppler effect. They transmit sound pulses into the water at a known frequency. Due to the interaction of these acoustic waves with moving particles in water, such as suspended sediment or small organisms, the frequency of the reflected sound waves shifts through the Doppler effect. This shift in frequency will be related to the velocity of the water carrying those particles.

By measuring the frequency shift of reflected sound waves from different directions and at different depths, ADCPs can calculate multi-dimensional-usually horizontal and vertical-velocity components of the water flow. An ADCP profiler uses several acoustic beams to derive a more comprehensive understanding of the current structure. This will be able to establish detailed current profiles that can show just how the water is moving at varying depths along the coast of Bandarbeyla.

5. What's needed for high-quality measurement of Bandarbeyla coastal currents?

Measuring coastal currents around Bandarbeyla will require certain qualities in the equipment; namely, it has to be manufactured with reliable materials that can resist hard conditions in a marine environment. The materials of the equipment should be able to bear salty water that can provoke corrosion, waves that may exert mechanical tensions on the device, and changes in temperature.

Equipment size: Small in size, for easy deployment and installation in any environment, whether on boats, on the seabed, or on buoys. Light weight for easy handling and transportation is an added advantage. Power consumption shall be low enough to enable long-term operation without frequent battery replacement or large-scale power supply. Cost-effectiveness: It also needs to be cost-effective enough to enable large-scale measurements.

For ADCPs casing, the material of choice would be a perfect one made of titanium alloy. The titanium alloy is characterized by high strength that enables it to bear all kinds of mechanical forces in the marine environment. It is highly resistant to corrosion by seawater, ensuring the service life of the equipment. Its relatively lower density compared with other metals makes it suitable for applications where weight is a concern, which goes well with the requirement of the device for measuring coastal currents.

6. Selection of Equipment Depending on the Purpose of Measurement

Depending on the Purpose of Use

• Ship-borne ADCP: This can be used when a measurement is necessary with the ship in motion. It keeps on giving data regarding currents while the ship is sailing off the coast. In research vessels, it is useful during surveys, for naval ships during surveys.
• Bottom-mounted ADCP: It provides detailed information on the current pattern in a specific area over a long period, which is useful for understanding the local hydrodynamic conditions and is ideal for long-term and stable measurements at a fixed location on the seabed.
• Buoy-mounted ADCP: It is good for the measurement of surface and near-surface currents when the buoy is deployed in coastal waters. This helps in studying the interaction between the atmosphere and the ocean surface currents.

Based on Different Frequencies

• The 600kHz ADCP can be used on relatively shallow coastal waters with up to 70m of depth because it gives current measurements quite accurately within this range.
• For waters from 70m to 110m, the 300kHz ADCP can give better results in terms of providing reliable data due to its ability to effectively penetrate the water column.
• For deeper waters up to 1000m such as in some parts of the Indian Ocean near Bandarbeyla, a 75kHz ADCP is the most suitable option to measure the currents throughout the water column.
• There are well-known ADCP brands like Teledyne RDI, Nortek, and Sontek. However, for those looking for a cost-effective option, the China Sonar PandaADCP is a good alternative. It's made of all-titanium alloy material and offers an excellent cost-performance ratio. You can visit their website at https://china-sonar.com/ for more information.

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