How can we measure the coastal currents of Jazan?

1. Where is Jazan?

Jazan is a city in southwestern Saudi Arabia, nestled along the Red Sea coast. It is a region rich in history and culture, with a unique blend of traditional Arabian and modern influences.

The city is enveloped in a landscape that reveals arid plains and, farther back, mountains, lending a beautiful contrast to the azure waters of the Red Sea. The Jazan coastline is dotted with sandy beaches and small inlets that shelter local fishermen and provide playgrounds for beachgoers. The adjacent Red Sea is a haven for marine life, with its warm, clear waters hosting coral reefs and a variety of fish species. The bays around Jazan-for example, the Al - Lith Bay-offer tranquil and well-protected waters which are important in maritime activities and also influence the patterns of the coastal currents. This is also the area where groves of date palms and agricultural activities on land, which is a little more fertile inland, could be found.

2. What are the coastal currents near Jazan like?

In the coast of Jazan, the coastal current is determined by several reasons. First, the tide is considered a fundamental aspect. Tides in the Red Sea, produced by the gravitational pull of both the moon and the sun, provide a periodic rise and fall in water level known as the tidal flow. These tidal currents can also vary in strength and direction depending on the lunar cycle.

Another important aspect would be wind patterns. The surface currents can also be immensely influenced by prevailing winds within the region. Certain seasonal winds might keep pushing the water in one direction in any given area, which thereby creates stronger currents at any given coastline. The pattern is influenced further by the local bottom topography and shape of coastline. These irregularities at the bottom may deflect or channel the water, while the shape of the bays and headlands is able to accelerate or slow down the currents. Besides, temperature gradients in the water column, induced by differential heating and cooling of the water, can contribute to the generation and modification of coastal currents.

3. How to observe the coastal water flow of Jazan?

Methods of observing the coastal water flow around Jazan are many and varied. One is the surface drifting buoy method. This involves releasing buoys onto the water that float on the surface. These buoys have trackers on them, such as GPS, that allow researchers to know the path the buoys have taken over a certain period of time. From this path and speed, the direction and speed of the surface currents can be estimated.

The moored-ship method is also utilized. A ship is moored in place, and from it current-measuring instruments are dropped. Such instruments can measure the velocity and direction of the water at several depths. This method however has its drawbacks because the ship itself disrupts the local current patterns, and being stationary, the area of observation is restricted.

The ADCP flow meter method is a rather advanced and efficient technique for the measurement of coastal currents. ADCPs can be mounted on several platforms: boats, buoys, or even placed on the seabed. Thus, they can provide a detailed profile of the current velocity from the surface to a certain depth with better insight into the structure of the current.

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

The ADCPs operate on the principle of the Doppler effect. They transmit acoustic pulses into the water. The interaction of these pulses with the particles or any other objects in the water, which move with the current, changes the frequency of the reflected signal. This frequency shift, commonly referred to as the Doppler shift, is directly proportional to the velocity of the moving objects and thus the velocity of the water current.

It works by measuring the Doppler shift in the reflected acoustic signals that come from all directions and depths. By computing these Doppler shifts, it works out the water current velocity and direction of flow for a series of measurement points. There are normally several transducers in a device performing this operation, which broadcast and receive acoustic signals at a rapid rate, in order to build up the three-dimensional current profile.

5. What is needed for high-quality measurement of Jazan coastal currents?

In order to provide high-quality measurement of the coastal currents near Jazan, a number of features need to be included in the equipment. First, the materials used in manufacturing the equipment must be both reliable and durable. Its casing should be resistant against the corrosive action of saltwater and against the pressure that water at different depths would exert on it. A small size and low weight are advantageous for many reasons, such as its easy installation and deployment on various platforms such as buoys or small vessels.

Low power consumption is very necessary since most of the time measurements are to be taken on a long-term basis in which power sources such as batteries need to last. Also, cost-effectiveness would be an important consideration since large-scale measurements will normally be required. Using titanium alloy for the casing of ADCPs is a good option. The corrosion resistance of titanium alloy is excellent, making it well-suited for the salty environment of the Red Sea. It is also strong enough to handle the pressure of the water column.

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

The purpose of measurement is a major concern when choosing the right equipment for the current measurement around Jazan. The ship-mounted ADCP would suit the purpose of the ship-based measurement as it can display the current information in real time when the ship moves across the water. Bottom-mounted or "sit-on-bottom" ADCP can be deployed for near-bottom measurement. This type of ADCP profiler is able to measure the currents near the bottom, which is very important for understanding the interaction between the bottom and the water column. In the case of long and wide-area measurements, a buoy-mounted ADCP will be suitable.

This, too depends on the choice of water depth. Water with up to 70m may often suffice for a 600kHz ADCP. Waters ranging to 110m use 300kHz more appropriateness, whereas above and as deep as up to 1000m deep waters are well fit by using a 75 kHz.

There are well-known ADCP brands like Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also worth considering. It is made of all-titanium alloy material, providing excellent durability and performance. Moreover, it offers an incredible cost-performance ratio. You can find more information about this brand on their website: https://china-sonar.com/.

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