How can we measure the coastal currents of Cyprus?

1. Where is Cyprus?

Cyprus is an island country in the Mediterranean Sea at the crossroads of Europe, Asia, and Africa. It is the third-biggest island in the Mediterranean, with an area of 9,251 square kilometers. The island is divided into two main parts: the internationally recognized Republic of Cyprus, located in the south, and the self-declared Turkish Republic of Northern Cyprus, recognized only by Turkey, in the north.

Geographically, Cyprus lies about 40 miles south of Turkey, 60 miles west of Syria, and 220 miles east of Greece. Its coastline measures over 648 kilometers and is very variable: long, sandy beaches on the southern coast, such as in tourist areas like Limassol and Paphos; a more rugged northern coast with rocky cliffs and small coves in many places.

Culturally, Cyprus is complex and rich in history. Throughout the ages, it has come under the rule of the Greeks, Romans, Byzantines, Ottomans, and British. These have left indelible imprints on its land, marked by archaeological sites such as Kourion on the south to Salamis in the north, testifying to its rich heritage. They draw most of their livelihood from the sea by means of fishing and other maritime-related activities. Most of the different kinds of sea life, from fish to turtles and dolphins, have been seen in the coastal waters of Cyprus.

2. What is the condition of the coastal currents near Cyprus?

The characteristics of the coastal currents around Cyprus derive from various combined factors, of which wind plays the leading role. Several winds act upon the Mediterranean Sea. The dominant north-westerly winds may drive surface waters inshore and therefore create an onshore current. Such an onshore current might carry in nutrients from the open sea that are beneficial to the growth of phytoplankton and other marine organisms. Easterly winds, on the other hand, may push the water away from the shore and thus create an offshore current.

Although small in the Mediterranean as compared with other seas, tidal forces also play their role in current dynamics. The tides ebb and flow and interact with the wind-driven currents. The water level is higher at high tide, and thus the direction and speed of the current may change. Another important factor is the bathymetry of the region. The bottom topography around Cyprus is very irregular, with several underwater valleys, ridges, and reefs that could accelerate, decelerate, or alter the direction of currents. For example, a narrow underwater channel may constrict the flow of water, therefore increasing the speed of the current, while a big reef may act like a barrier to the current, deflection being the result.

The coastal currents off Cyprus are driven by the more general circulations of the Mediterranean Sea as well. This is situated within that area of general circulation that happens within the basin, involving Atlantic water inflow through the Strait of Gibraltar, and between its different basins, very intricately. The river runoff of the few small rivers of the island supplies more freshwater in the coastal zone and develops some density-driven currents that interact with the pre-existent wind- and tide-driven ones.

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

Surface Drifting Buoy Method

Surface drifting buoy-a rather simple method adopted for surface level observation of coastal currents. Small buoys are fitted with GPS tracking devices and placed into the water. As the buoys drift due to currents, their movement is tracked over a period of time. By analyzing the path of the buoy, scientists can approximate the speed and direction of the surface currents. However, this technique has some disadvantages. Surface winds can significantly influence the movements of the buoys, and they tend to drift away from the actual current path. Besides, it provides details only about the surface layer of the water, not the currents at greater depth.

Anchored Ship Method

An anchored ship can act like a fixed platform for making the current measurement. Current meters are suspended at several depths beneath the ship. These meters could record the current's velocity and direction at each depth, taking a very good, specific vertical profile of the currents at the particular location. However, this is limited in terms of the area that can be validly covered. The collected data characterizes only a very proximate area to where the ship was, and even the very presence of the ship might interfere with natural flow.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP has become one of the preferred methods for measuring coastal currents near Cyprus. ADCPs use sound waves to measure the velocity of water at multiple depths simultaneously. They can be deployed from ships, moored to the seabed, or attached to buoys. This flexibility enables a more comprehensive data collection. The reason ADCPs are more effective in measuring the actual current conditions is that they are less affected by surface-level disturbances related to wind. They can give a three-dimensional view of the current structure, including both horizontal and vertical flow components.

4. How do ADCPs using the Doppler principle work?

An ADCP flow meter is based on the principle of the Doppler effect. The principle of operation begins when an ADCP sends high-frequency sound waves out into the water. These waves hit small particles in the water, like plankton or sediment, or even small bubbles. These particles reflect the sound waves back to the ADCP. The frequency of the scattered sound waves received by the ADCP is different from that of the sound waves sent. This frequency shift is known as the Doppler shift and is directly related to the velocity of the particles and thus the water to the ADCP.

Most ADCPs are multi-transducer-beam devices. By the measurement of the Doppler shift in each beam, the ADCP can compute the velocity components of the water in various directions. By vector addition of these velocity components, the ADCP can work out the three-dimensional velocity of the water. This enables a highly accurate depiction of how the water is moving in all directions, which is very important for mapping with great accuracy the currents in the area.

5. What is required for high-quality measurement of Cyprus coastal currents?

Equipment Material Reliability

The material used to make the casing of an ADCP current profiler will be of utmost importance to realize high-quality measurements in the coastal waters of Cyprus. The ideal casing for the ADCP would be one made from a titanium alloy. A titanium alloy has good corrosion resistance, and the equipment will constantly be exposed to the corrosive seawater. It will not degrade from long-term exposure to salinity with no significant degradation and will ensure that the longevity and reliability of the ADCP are maintained. Besides, the high strength-to-weight ratio means the ADCP can maintain its structural integrity even under strong currents or rough seas.

Size, Weight, and Power Consumption

The ADCP current meter should be designed to be small in size and lightweight. Compact design helps in deploying it anywhere. For example, it is easy to mount on a small research vessel or buoy. The size reduces the effect of the flow field that has to be measured. Another important factor is the consumption of low power, which keeps the operation of an ADCP profiler working for quite a long period without any battery replacement or any external power supply. This is especially crucial in long-term deployments of sensors in coastal areas around Cyprus.

Cost-effectiveness

This will, in turn, enable large-scale and comprehensive monitoring of the coastal currents of Cyprus at cost-effective prices. The more economical an ADCP meter is, the more research institutions, environmental monitoring groups, and local initiatives can buy the equipment and collectively collect the data. This is very much necessary to achieve a decent understanding of the complex dynamics of coastal currents.

6. How to Choose the Right Equipment for Current Measurement?

Based on Usage Purpose

• Shipborne ADCP: This type of ADCP is mounted on a moving ship. This is very suitable for the work of conducting large-scale surveys of the coastal currents around the entire island. The ADCP mounted on the ship would be able to continuously measure currents while the ship cruises along the coast, thus enabling a broad-scale view of the current patterns over a large area. This would be useful for preliminary research or when studying changes in the currents over a wide geographical range around Cyprus.
• Bottom-mounted ADCP: Bottom-mounted ADCPs are mounted on the seafloor for fixed-point, long-term monitoring. They can provide continuous data for the current structure of a certain depth and location, which is useful in understanding local hydrodynamics, such as the ordinary behavior of the current in a specific bay or near a particular feature along the coast of Cyprus.
• Buoyant ADCP: Buoyant ADCPs are attached to a floating buoy and thus can move with the surface currents. They are well-suited for monitoring the surface and near-surface current patterns. They can also be used to track the movement of water masses over time, which is important for studying the transport of nutrients, pollutants, or marine organisms in the coastal waters around Cyprus.

Based on Water Depth

• In areas of 70m or less, the 600kHz ADCP is ideal: this makes use of the higher frequency to return very small details at shorter waters. Its very high resolution output regarding current structure is suited in defining minor scales changes within nearshore currents.
• A 300kHz ADCP is appropriate for water depths around 110m. It offers a good balance between measurement range and resolution. It would give better penetration into the water column compared to a 600kHz ADCP while still giving fairly accurate measurements for mid-depth coastal waters.
• A 75kHz ADCP is recommended if the water is as deep as 1000m. Lower frequency of the sound waves can reach deeper though the resolution may be lower than the higher - frequency ADCPs. In this way it will be suitable for measuring the currents in the deeper parts of the Mediterranean Sea around Cyprus.

There are several well-known ADCP brands in the market such as Teledyne RDI, Nortek and Sontek. However, for those seeking a cost-effective yet high-quality option, the China Sonar PandaADCP is a great choice. Made of all-titanium alloy, it offers excellent durability and performance at an affordable price. It is an economic-class ADCP that provides great value for money. You can find more information about it on their official website: (https://china-sonar.com/).

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