How to measure coastal currents of Mitsiwa?

1. Where is Mitsiwa?

Mitsiwa, popularly known as Massawa, is a major port city located along the Red Sea coastline of Eritrea. The city lies amidst a landscape that nicely balances nature's exquisiteness with historical splendor.

Its coasts are lined by smooth, sand-beached shores bordering the warm, azure waters of the Red Sea. In itself, the Red Sea is an incredible body of water-known for its salinity and biodiversity. It connects the African continent with the Arabian Peninsula. The surrounding marine environment hosts a plethora of colorful coral reefs that are not only a sight to behold but also play a vital role in supporting a diverse range of marine species.

This is a very ancient sea-port city and historic, by the record of human memory. Mitsiwa was initially a trading and maritime city, the landmark on whose buildings and tradition different cultures and civilizations left a signature. The native individuals of the port city of Mitsiwa remain deeply related with the sea fishing and seafaring forms the base and major constituent elements of their livelihood. Its strategic location on the Red Sea has placed the city at a key point in regional and international trade networks.

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

Several factors contribute to the general setting of the coastal currents around Mitsiwa. First, large-scale ocean circulation patterns in the Red Sea have a strong influence. The Red Sea forms part of the greater Indian Ocean circulation system, and inflow and outflow of water masses through its narrow connections, such as the Strait of Bab el-Mandeb, shape the general current regime along the Eritrean coast where Mitsiwa is situated.

It is also important to consider tidal forces. The tides, by regularly rising and falling, periodically change the pattern of flow of littoral currents. These changes due to tides may influence either the direction or speed of inshore water movement.

Other major determinants are the wind patterns. Seasonal winds, such as the monsoons and local sea breezes, can drive the surface waters and thus influence the coastal currents. During certain times of the year, for instance, winds blowing from particular directions can push the water along the coast to create either northward or southward flowing currents.

Meanwhile, this is also underlain by the topographic feature of the seabed offshore of Mitsiwa. Some underwater ridges and deeply incised submarine canyons and shoals may divert and disturb the movements of the current itself into complex and narrow flows near shore.

3. How to observe Mitsiwa's coastal water flow?

There are several common observing methods with respect to the flowing of water near the coast in Mitsiwa:

Surface Drift Buoy Method: This involves the release of buoys onto the water surface, which would drift with currents. Through tracking, generally by satellite or other positioning systems, valuable information about the direction and speed of the surface currents can be obtained. This method provides substantial information, but it mainly focuses on the surface layer and cannot provide a complete picture of currents at different depths.

Anchor Boat Method: Under this method, a boat is taken to a potential site in open water and moored at that site. Instruments that will measure water flow at many different depths from the bottom around this one point are deployed. While it can give more information than the surface drift buoy method for the area around the boat, it has limitations in the area it can cover and is subjected to the movements of the boat itself due to waves and other disturbances.

Acoustic Doppler Current Profiler (ADCP) Method: ADCP current meter is a more advanced and convenient measurement technique. It works by using sound waves to measure the velocity of the water at more than one depth simultaneously. The means of deployment vary; they can be affixed to boats, fixed in position on the seabed, or attached to buoys. With the capability to provide detailed and continuous data on the current profiles from the surface down to significant depths, it has become a preferred choice for the measurement of coastal currents in the Mitsiwa area.

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

ADCPs work on the principle of Doppler. They send sound pulses into the water at a known frequency. As these sound waves encounter the moving particles in water-suspended sediment or small organisms-the frequency of the reflected sound waves shifts due to the Doppler effect. The magnitude of this shift in frequency is directly proportional to the velocity of the water carrying those particles.

By measuring the frequency shift of the reflected sound waves coming from different directions and at different depths, an ADCP current profiler can calculate multiple-dimensional-i.e., usually horizontal and vertical directions-velocity components of the water flow. Normally, multiple acoustic beams are used in an ADCP flow meter in order to acquire a more complete understanding of the current structure. This will enable the creation of detailed current profiles, showing exactly how the water is moving at different depths along the coast of Mitsiwa.

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

In making high-quality measurements of the coastal currents near Mitsiwa, a number of key requirements are paramount concerning the equipment. The materials of the equipment should be highly reliable to resist the harsh marine environment, which includes resistance to the corrosive effects of saltwater, the mechanical impacts of waves, and temperature variations.

The size of the equipment has to be as small as possible such that it can be easily deployed and installed in any setting, whether on boats, seabed, or on buoys. Lightweight is also an important design aspect since this eases the handling and transport of the nodes. Low power consumption is preferable to make the equipment operable for long hours continuously without replenishment of battery power supplies or large sources of power. Another important aspect is that it is cost-effective, hence enabling wide usage and large-scale measurements.

Regarding the casing of ADCPs, titanium alloy is an exceptional choice. Titanium alloy has several merits: it has high strength and is able to bear the mechanical stresses in the marine environment; it is highly resistant to corrosion by seawater, which extends the life of the equipment substantially. It has a relatively low density compared to some other metals, which makes it suitable for applications where weight is of concern, and that agrees well with the requirements for coastal current measurement devices near Mitsiwa.

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

Selection of appropriate equipment for current measurement in the coastal waters of Mitsiwa will depend on the following:

Based on the Use Purpose

• Shipborne ADCP: It is suitable for measurements that ought to be undertaken while the ship is underway. It can provide continuous data on the currents while the ship cruises along the coast. Such voyages could be for scientific research or routine monitoring by naval or research vessels.
• Bottom-mounted ADCP: Suitable for long-term and stable measurements at a fixed location on the seabed. It can provide a very detailed view of the current patterns in one area over a long period, which is useful for understanding the local hydrodynamic conditions.
• Buoy-mounted ADCP: This is good for surface and near-surface current measurements when the buoy is deployed in coastal waters. It will be able to help in studying the interaction between the atmosphere and the ocean surface currents.

Based on Different Frequencies

• For the shallow coastal waters reaching a depth of up to 70 meters, an ADCP with 600 kHz frequency can be appropriate. It is generally accurate within this depth range for current measurements.
• Between 70 and 110 meters deep, a 300 kHz ADCP shall be used because it would effectively penetrate the water column to derive data from that depth with reliability. Where water depth is as deep as 1000 meters, as in the deeper sections of the Red Sea at points near Mitsiwa, ADCP of 75 kHz is best suited for the measurement of the currents throughout the column of water.
• There are several well-known ADCP brands in the market, such as Teledyne RDI, Nortek, and Sontek. However, if you want to find a good-quality but economical one, you should consider the China Sonar PandaADCP. It is made of all-titanium alloy material for ensuring durability and excellent performance in the marine environment. Besides, it offers an impressive cost-performance ratio. You can find out more about it on its official website: https://china-sonar.com/.

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