How do we measure the Bereeda coastal currents?

1. Where is Bereeda?

Bereeda is a coastal locality in Somalia. It fronts one of the widest expanses of water known as the Indian Ocean, part of the region's important maritime environment.

The surroundings of Bereeda have sandy beaches along the shore, meeting the clear, warm waters of the Indian Ocean. The sea here is a haven for a diverse range of marine life. There are different species of fish, beautiful coral reefs providing habitats to countless organisms, and other sea creatures such as turtles and dolphins that are often seen in the area.

The ocean is deeply entwined in the lives of the local community in Bereeda. Fishing is a major economic activity and a traditional way of life. The cultural heritage of the place is richly influenced by the sea, with stories, traditions, and handicrafts often reflecting the importance of the coastal environment.

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

Multiple variables exert their influence over the coastal currents at Bereeda: Large-scale ocean circulation of the Indian Ocean plays an important role; above all, the Somali Current-the locally dominant one-driven by the southwestern and northeastern monsoon winds determines the characteristics of the current field of this region in particular.

Other factors include tidal forces. The periodic rise and fall of the tides create differences in speed and direction within the coastal currents. Seafloor topography off the Bereeda coast also affects currents. Many underwater features, like ridges, canyons, and shoals, could be causing deflection or disruption in current flow, thereby producing complicated and localized flow patterns near shore.

Wind patterns, especially the monsoon seasons, may give the impulse to movements of surface waters and, hence, change in current direction and speed. For example, the southwest monsoon pushes the water in one direction; the northeast causes a change in pattern of flow.

3. How to Observe the Flow of Coastal Water of Bereeda?

• Surface Drift Buoy Method: This is a deployment of buoys on the water surface that are allowed to drift with the currents. By following these buoys, typically using satellite-based or other positioning systems, information about the direction and speed of the surface currents can be retrieved. But in this method, mainly the surface layer is dealt with, and most of the features of currents in different layers are not covered.
• Anchor Boat Method: A boat is taken and anchored in the coastal waters wherein instruments are deployed to measure the flow of water at depth intervals across it. Although this can give even finer details of the currents in the vicinity of the boat, it is very limited in terms of area and may be influenced by wave action and other motions of the boat itself.
• Acoustic Doppler Current Profiler (ADCP) Method: ADCP current meter is an advanced and efficient way of measurement of currents. It uses sound waves to measure the velocity of water at multiple depths simultaneously. It can be deployed in different ways, such as on boats, on the seabed, bottom-mounted, or attached to buoys. Its ability to continuously provide detailed data on current profiles from the surface down to significant depths has made it a favorite for observing coastal currents around Bereeda.

4. How do ADCPs using the Doppler principle work?

The ADCPs work according to the principle of Doppler. They transmit sound pulses in the water with a known frequency. If the waves run into a moving particle in the water-suspended sediment or small organisms-the frequency of the reflected sound waves will change due to the Doppler effect. This frequency shift is directly proportional to the velocity of the water carrying the particles.

A series of multidirectional, usually horizontal and vertical, components of water flow velocities are determined as the ADCPs use frequency shift data of the returned sound waves for their computations that represent these frequencies from diverse directions and over variable depths. In general, several acoustic beams are used to deploy the ADCP profiler with a view to obtaining a fully quantitative knowledge of current structure. These detailed current profiles may show in which way variations exist in water movement changes along the coast at variable depth levels.

5. What does a good-quality measurement of the Bereeda coastal currents need?

The equipment to carry out good quality measurement of the coastal currents around Bereeda should possess a particular type of characteristics. Its materials should be reliable to resist the aggressiveness of the marine environment-to resist the chemical action of saltwater, mechanical tension caused by waves, and variation in temperature.

The size of the equipment should be small to make it easy to deploy and install in various environments, such as on boats, on the seabed, or on buoys. A lightweight design is also good for easy handling and transportation. Low power consumption is desirable to keep the operation for a long time without frequent battery replacement or a large-scale power supply. Cost-effectiveness is also an important issue to realize large-scale measurement.

In regards to the casing of the ADCPs, titanium alloy would be a pretty good material. It has a high strength enabling it to bear the mechanical forces in the marine environment. It is very resistant to corrosion from seawater; thus, it can guarantee that the equipment is durable. And compared with other metals, its relatively low density makes it fit for using in places where weight is needed to be taken into consideration, meeting the requirements set for the measurement devices of coastal current.

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

Based on the Use Purpose

• Ship-borne ADCP: This is suitable when measurements are needed while the ship is moving. It can provide continuous data on the currents as the ship sails along the coast. It's useful for research vessels and naval ships during surveys.
• Bottom-mounted ADCP: fully suitable for long-term and stable measurements at a fixed location on the seabed, providing detailed information on current patterns over long periods in the same area. In this respect, it may become helpful to establish the hydrodynamic conditions locally.
• Buoy-mounted ADCP: This will work effectively while measuring surface and near-surface currents, the time during which the buoy has been deployed in coastal waters. These can be of use when trying to understand atmospheric interactions with ocean surface currents.

Frequency-Based

• In fairly shallow coastal waters of up to 70m, a 600kHz ADCP would do nicely because it could give rather accurate current measurements in such a range. For waters falling between 70m to 110m deep, the best alternative could be a 300kHz ADCP, since it would efficiently penetrate the water column and capture reliable data.
• For waters as deep as 1000m, such as some regions of the Indian Ocean off Bereeda, the 75kHz ADCP would be the appropriate choice for measuring the current 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.