How to measure the coastal currents of Mocha?

1. Where is Mocha

Mocha is an ancient seaport nestled in Southwestern Yemen with unparalleled historical background. The richly storied town was dramatically poised between the Red Sea's remarkable marine-life and strategic placement with regard to global sea borne trade.

The landscape is a mixture of deserts, which stretch inland, while the Red Sea waters, in vibrant color, lap at its coasts. The coastline of Mocha features sandy beaches with rocky formations, creating a picturesque and diverse coastal setting. The waters here are home to a plethora of marine species, from colorful corals to various types of fish, making it a popular destination for diving enthusiasts when the security situation permits.

Mocha is full of human cultural heritage. Once upon a time, Mocha was an important busy port for coffee trading; the name gained the fame of the best coffee exported worldwide from here. The sea has a lot of deep-seated traditions within the local community. Fishing has been an important part of the people's livelihood for generations, and the town's architecture still bears the marks of its historical maritime glory with buildings that were designed to withstand the coastal climate and facilitate trade activities.

The Red Sea at Mocha is one of the most critical waterways, connecting several regions, which is quite vital in international shipping. It is also a part of immense ecological importance due to its unique combination of warm waters, coral reefs, and varied marine life.

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

The coastal currents near Mocha are influenced by several factors. Tidal forces predominate in. Tides in the Red Sea are forced by the gravitational pull of the moon and sun. The semi-diurnal tides produce a regular pattern of water movement, with the ebb and flow causing variations in strength and direction in the coastal currents. The tidal range may vary from the lunar cycle and other astronomical factors that in turn affect the interaction of currents with the shoreline.

The wind patterns also play a major role. The prevailing winds in an area may drive the surface water, developing currents that may be added to or opposed to the tidal currents. In those seasons when stronger winds occur, they may push the water in one direction or another and create more pronounced current patterns. Also, the interaction of wind-driven and tidal currents creates a complex, dynamic flow regime near the coast.

The other determining factor is the seafloor topography off Mocha. Seafloor topography with features ranging from coral reefs, to shoals and channels will tend to bend and alter the current. For instance, water that approaches a reef can be forced to move around or over it in a way that the velocity and current direction are altered. Variations within this type of seafloor morphologies will also significantly contribute to coastal current patterns.

3. How to Observe Coastal Water Flow of Mocha?

Surface Drifting Buoy Method

In this method, buoys that are designed to float on the water surface are released and left to drift with the currents. The movement of the buoys is followed over a certain period of time using satellite-based tracking systems or other positioning technologies for data regarding the direction and speed of the surface currents. However, this technique gives information mostly on the surface layer and cannot give an overall view of the currents in the entire water column.

Anchor Mooring Ship Method

A ship is anchored at a given location in the coastal waters. Instruments such as current meters are then lowered from the ship to measure the flow of water at different depths. This allows for a more detailed observation of the existing conditions of a point in the water column. However, it is relatively a stationary method and cannot fully capture the complexity that may arise in coastal current patterns over a greater area.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) method is an advanced and more efficient way of measuring coastal currents. It also measures the water velocity at different depths all at once using acoustic pulses. The sensor emits sound waves, and by calculating the Doppler shift of the reflected waves, it calculates the speed and direction of the water movement. The instruments can be installed on boats, buoys, or even directly on the seabed to enable the coverage of any location and obtain a profile of the current with good resolution throughout the water column.

4. How do ADCPs using the principle of the Doppler work?

ADCPs work on the principle of the Doppler effect. They send acoustic signals into the water at known frequencies. As these signals collide with the moving particles of water, the frequency of the reflected signals is changed by the Doppler effect. This shift in frequency is measured by the ADCP profiler, and through mathematical algorithms, the velocity of the water relative to the instrument is determined.

Because ADCPs have the ability to emit signals at various angles and frequencies, it can measure the velocity components along different directions, including both horizontal and vertical directions, and also at different depths of the water column. This would allow a full profile of the water flow, hence giving detailed information about the structure of the coastal current and its dynamics.

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

For high-quality measurement of the coastal currents near Mocha, there are several requirements of the measurement equipment. The materials used in the equipment are required to be highly reliable because, under such a marine environment, there is salt water corrosion, high humidity, and the impact of waves. So the equipment should bear these conditions for a long period.

It should also have an advantageous small size, light weight, and low power consumption. These ensure the equipment is easy to install and transport either to a small fishing boat or even on a floating buoy. Low power consumption ensures continuity of operating time without often having to replace the batteries or access a huge power source.

Another important consideration is cost: equipment, when deployed for large-scale measurements often required to fully comprehend the complex current patterns along coastlines, should be moderately affordable to allow multiple units to be put in place at various points of the coastline.

For ADCPs, casing made of titanium alloy is highly recommended. Firstly, the application of a casing made of titanium alloy guarantees excellent resistance to corrosion caused by the saltwater environment around Mocha. Besides that, it has an elevated strength-to-weight ratio, which ensures robust protection of the internal parts of the ADCP meter and maintains low overall weight.

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

Depending on the Usage Purpose

• Shipborne ADCP: This is right for when you want the measurement of currents while the ship moves along the coast. It can, in this case, continuously gather data while the ship moves, therefore providing a wide vision of the current variations over the different sections of the coastline.
• Bottom-mounted ADCP: This is good for fixed-point monitoring of given locations from the seabed. The data given is in detail for the current condition right above it, hence providing valuable input for understanding local flow patterns over longer time intervals with precision.
• Buoy-mounted ADCP: If there is a need to monitor extensive surface and upper layers of a water column for a longer period and not be constrained by staying either on a ship or anchored at a fixed bottom position then Buoy-mounted ADCP is optimal.

Based on water depth

• In water as deep as 70m, 600kHz ADCP normally works with good resolution in relatively shallow water along the coast near Mocha.
• For a 300kHz ADCP with measurements in as much as 110m of water, more resolution is allowed and therefore higher quality velocity data.
• The 1000m deep is justified by the fact that in waters, deeper and for depth with current measurement accuracy increased can reach this limit, requires an ADCP of 75 kHz.

Some renowned brands in the ADCP field are Teledyne RDI, Nortek, and Sontek. However, there is also a very good Chinese ADCP brand: China Sonar PandaADCP. It is all made of titanium alloy material and enjoys an incredibly high cost-performance ratio. You can check their website at: https://china-sonar.com/.

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