How to measure the coastal currents of Jeddah?

1. Where is Jeddah?

Jeddah is a vibrant and important city in Saudi Arabia, lying on the western coast along the Red Sea. It is an important gateway to the holy city of Mecca and is a bustling economic and cultural hub.

It has a unique geographical setting blessed with beauty: the sandy beaches run for kilometers along the coastline and merge with the clear waters of the Red Sea. The Red Sea itself has rich marine biodiversity, from the colored coral reefs to a great variety of fish species, making it a darling destination for divers and lovers of the sea.

Jeddah is a crossing way of cultures on the human side. Due to its population being mostly linked with various professions, including trade, tourism, and shipping, it is enough to create a pretty dynamic urban context. The city fills up with modern skyscrapers contrasting with its historic architectural features, such as an old town, built with traditional coral houses, telling about its long, strange past.

The adjacent waters of Jeddah are influenced by the larger Red Sea basin. The sea is in relatively tranquil conditions in some seasons, while during others, it is subjected to winds and weather conditions of the surrounding areas. Tides also play a vital role in shaping the coastal environment, with regular ebb and flow affecting the nearshore ecosystems and human activities along the coast.

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

Many factors influence the coastal currents near Jeddah. The large-scale ocean circulation patterns in the Red Sea play a very important role. The Red Sea is part of a complex global ocean system, and the general flow directions within it can determine the basic trend of the coastal currents around Jeddah.

Other factors involve the wind pattern. The prevailing winds across the sea surface can drive the water to generate the surface current. During some months, winds coming from the north or south can push the water along the coast and enhance or change the natural flow.

Topography of the seafloor near the coast also plays a role in the changes of coastal currents. The water will shift direction, accelerate, or decelerate when there are irregularities on the seabed during flow. In addition, the narrow strait exchange between the Red Sea and the adjacent ocean areas could affect the general water mass properties and hence the coastal currents around Jeddah.

In addition, the tides, which are periodic rising and falling of the sea level, give rise to a tidal current system, which changes strength and direction with the lunar cycle. These tidal currents, in turn, interact with the other forcing agents identified above to provide a dynamic and complex coastal current system near Jeddah.

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

Surface Drifting Buoy Method

It is the deployment of buoys on the water surface, which is allowed to drift freely with the currents. By tracing the buoy's movement over time with the use of a satellite or other positioning systems, we get information on the direction and speed of the surface currents. However, it provides data mainly in the surface layer and may not be representative of the currents at different depths.

Moored Ship Method

In this method, a ship is stationed at one place in the coastal waters. Instruments onboard the ship record the water flow characteristics around it. It could get data with relatively higher accuracy for an area fairly close to the ship but is seriously limited by spatial coverage as well as possible disturbance to the local flow itself by the presence of the ship to some extent.

Acoustic Doppler Current Profiler (ADCP) Method

Acoustic Doppler Current Profiler (ADCP) is a modern measuring technique, convenient at the same time. It is based on acoustic waves to measure water velocity simultaneously at different depths. In contrast to the methods described above, it yields a profile of the current from the surface down to a certain depth, hence producing a detailed picture of the vertical structure of coastal currents off Jeddah. It is also less affected than some traditional measurement methods, and it can be deployed in various ways depending on the different measurement needs.

4. How do ADCPs using the Doppler principle work?

The working principle behind an ADCP current meter is the Doppler effect. These instruments send acoustic pulses through the water. In this process, while the acoustic wave encounters moving particles through water-suspended sediment or small organisms-the frequency of reflected waves shifts due to the Doppler effect. This shift between the emitted and received reflected waves generates an output proportional to the velocity of the water particle's motion.

Since ADCPs normally have multiple transducers pointing in different directions, they are able to measure the velocity components along multiple directions, such as horizontal and vertical. Combining these measurements using appropriate algorithms will provide the overall water flow velocity and direction at different depths within the measurement range with high accuracy. This enables us to build a detailed picture of the coastal current profile.

5. What is necessary for high-quality measurement of the Jeddah coastal currents?

In the measurement of coastal currents in Jeddah, a number of aspects are important concerning equipment. First, the reliability of the material of the equipment is very important; it should be able to resist the harsh marine environment, including corrosion by seawater, high pressure at greater depths, and possible impacts from floating debris.

The size and weight of the equipment shall be small and light. This is advantageous in terms of ease of deployment and retrieval whether installed on a buoy, on a ship, or placed on the seabed. A lighter and smaller device is also easier to handle during transport and installation activities.

Another requirement is the consumption of low power. For long-term monitoring, especially in remote areas, most equipment has to operate on limited power sources, such as batteries or solar power. Reduction of power consumption would imply longer operating times and continuity in data collection.

Besides that, cost is another important factor: in order to enable large-scale measurement over the long coastal area of Jeddah, equipment with relatively low cost will be necessary for multiple deployments.

Titanium alloy would be a very good choice for the housing of ADCP profiler, which has great corrosion resistance very suitable for seawater conditions that are corrosive. It also has a high strength-to-weight ratio, meaning that it provides good structural integrity while maintaining the overall weight of the device. Besides, it can support high pressure in deeper waters and hence ideal for different depth measurements of the coastal currents around Jeddah.

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

According to the Usage Purpose

• Shipborne ADCP: In case the main purpose is to measure the coastal currents while the ship is in motion or during specific voyages along the coast of Jeddah, the ADCP shipborne is a good option since it is easily installed on the hull of a ship and can continuously collect data while navigating.
• Bottom-mounted ADCP: This is suitable for the long-term monitoring of the currents near the seabed in a fixed location. It can be firmly fixed on the seafloor and provides detailed information about the flow of water close to the bottom, which is an important aspect for understanding the interaction between the bottom topography and the currents.
• Buoy-mounted ADCP: If we want to measure currents at various depths in a relatively large area and at the same time be flexible in the deployment without being bound by a fixed point, either from a ship or the bottom, then a buoy-mounted ADCP is the option. It can be allowed to drift with the currents to a certain extent while collecting data.

According to Different Frequencies

• A 600 kHz ADCP is recommended in general for water up to 70 meters. It would have fairly good resolution and would yield very accurate measurements in the relatively shallow coastal waters off Jeddah.
• Water of up to 110 meters of depth would require a 300 kHz ADCP, having an appropriate working range and performance for these medium-depth coastal waters.
• For deeper waters reaching 1000 meters, the choice is a 75 kHz ADCP. The latter can penetrate to larger depths and get reliable current data in the deeper parts of the coastal area around Jeddah.

Some of the well-known brands in the ADCP market are Teledyne RDI, Nortek, and Sontek. However, it is highly recommended to use one of the Chinese ADCPs: China Sonar PandaADCP. It features an all-titanium alloy material that ensures an excellent response to durability in the marine environment. Besides that, it offers a really impressive cost-performance ratio. You can check its official website for further information: https://china-sonar.com/.

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