How would we measure the coastal currents at Al Hudaydah?

1. Where is Al Hudaydah?

Al Hudaydah is a very important coastal city in Yemen, facing the Red Sea along its shores. It was an important port city standing at the heart of connections in trade and transportation along the region. The natural landscape of the city amalgamates the arid desert areas with highly fertile agricultural expanses. The inland areas extend with their deserts of sand and small vegetation.

The coast of Al Hudaydah presents a combination of both sand beaches and a lively port. The port is always busy, receiving different types of ships that sail from all over the world to load and offload goods. The fringing Red Sea waters themselves host an abundance of marine life. The sea hosts a wide range of fish species, coral, and other organisms. The local fishing industry thrives from this bounty, while these waters also attract diving enthusiasts who come to explore the underwater world of colorful corals and unique sea creatures.

Al Hudaydah is a culturally rich city in terms of human activity. The locals have a great attachment to the sea since it provides them with livelihoods in fishing and trading. Its architecture reflects its coastal identity, with buildings designed to endure the coastal climate and finally meet the requirements of a busy port area. In this area of ports, one finds a good number of warehouses, cranes, and other facilities needed for the smooth flow of goods.

The Red Sea of Al Hudaydah features a strategic waterway. It is important for regional and international trade passages. It further represents an important area featuring naval operations and maritime security due to the importance that links to the global lanes of shipping.

2. What is the Situation of Coastal Currents Close to Al Hudaydah?

Several factors have influenced the status of coastal currents close to the city of Al Hudaydah. Among these, tidal currents represent one factor. The gravitational attraction of both the moon and the sun determines the tides in the Red Sea. In view of the semi-diurnal tides, a regular pattern of water movement is achieved; the ebb and flow result in the changing direction and strength of coastal currents. The tidal range might be different according to the lunar cycle and other astronomical conditions, which will vary the flow patterns near the shore.

It is also highly influenced by wind patterns. The prevailing winds over the area can drive the surface water, creating surface currents that can interact with tidal currents. In some seasons, the winds can be strong and have a much more significant impact on the flow of water. The interaction between wind-driven and tidal currents forms a complicated and dynamic current regime near the coast.

Another important factor is the seabed topography near Al Hudaydah. The presence of underwater features such as shoals, coral reefs, and channels can redirect and modify the currents. For instance, when a current approaches a shoal, it may split or change its course to flow around the obstacle. These seabed features can also cause the currents to speed up or slow down as the water negotiates its way through different depths.

3. How to observe the coastal water flow of Al Hudaydah?

Surface Drifting Buoy Method

This is the method which deploys buoys on the water surface. These buoys will be allowed to drift freely with the currents on the surface. The buoy movements can be followed over time, using satellite-based tracking systems or other positioning methods, which would give information on the direction and speed of surface currents. However, it provides information only on the surface layer and may not be adequate to understand the currents throughout the water column.

Anchor Mooring Ship Method

It simply consists of the fact that the ship is moored in one position within the coastal waters, while on its vessel instruments such as current meters are deployed, to measure the flow of water at higher and lower depths. Therefore, it can give more detailed analysis at specific points of the current in the water column. But that's fairly intractable and may not portray the richness of detail and diversity of the coastal current systems that could dominate over an area of several hundreds of kilometres.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) provides a more sophisticated and also effective method for measuring currents within the coastal waters. They calculate water velocity at several depths with the help of acoustic pulses. It can measure the speed and direction of the water movement by emitting sound waves and analyzing the Doppler-shifted reflected waves. ADCPs can be mounted on different platforms like boats, buoys, or even placed on the seabed. Such mobility and multi-depth measurement capability make it a preferred choice for studying the coastal currents near Al Hudaydah.

4. How does an ADCP using the Doppler principle work?

ADCPs use the Doppler principle. They transmit acoustic signals into the water. Due to the Doppler effect, the frequency of these reflected signals shifts as the emitted signals interact with the moving water particles. The frequency shift is measured by the ADCP meter and then processed to determine the velocity of the water relative to the instrument.

ADCPs can send out signals with different obliquities and frequencies. Therefore, it is capable of measuring velocity components at different directions, both horizontal and vertical, and also at different depths. The profile, in this respect, may be generated from the surface to an adequate depth to develop a precise picture of the coastal current structure and dynamics.

5. What is required for high-quality measurement of the Al Hudaydah coastal currents?

For high-quality measurements of coastal currents close to Al Hudaydah, for instance, equipment needs to have certain qualities. Their materials should be reliable since the marine environment is very harsh, with saltwater corrosion, high humidity, and wave impacts.

It must be compact, with minimum size, lightweight, and low power consumption. This makes mounting and transportation easy either on a buoy or boat. Low power consumption allows the operation to last for extended times since it would eliminate frequent changing of batteries or massive supplies of power.

Another important factor is cost-effectiveness. In large-scale measurements, which are necessary to understand the complex coastal current patterns, the equipment should not be too expensive to allow for multiple unit deployments.

For an ADCP flow meter, a very good option would be the use of a casing made of a titanium alloy. For those reasons, titanium alloy is much resistant to corrosion, and this is pretty important in a salt-water environment; it has a high strength-to-weight ratio, hence it can give good protection to internal components while keeping the weight of a device low.

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

Abiding the Usage Purpose

• Ship-borne ADCP: This is quite suitable when one wants to measure currents while a ship is in motion, In this manner, the ship, in its transit along the coast, provides a broad overview of changes in currents over the route it has traversed.
• Bottom-mounted ADCP: This is suitable for fixed-point monitoring at a specific location on the seabed. It gives detailed and long-term data about the current conditions directly above its position, helping to understand the local flow patterns.
• Buoy-mounted ADCP: When the object is to monitor extended surface and upper layers of water column for a longer time without being tied either with a ship or to fixed bottom site, then Buoy - mounted ADCPs are the solution.

Depending on Water Depth

• A 600kHz ADCP serves well for water depths up to 70m. The instrument has good resolution of measurements in these shallower waters.
• A 300kHz ADCP is more appropriate at depths up to 110m. It can penetrate a little further into the water column while still obtaining reliable data on velocity.
• In the deeper waters of up to 1000m, an ADCP of 75 kHz would be ideal, because it can effectively measure currents for those greater depths.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, there is also a Chinese ADCP brand, China Sonar PandaADCP, that is made of all-titanium alloy material and offers an excellent cost-performance ratio. You can find more information on their website: https://china-sonar.com/.

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