How will we calculate Manisa's coastal currents?

1. Where is Manisa?

Manisa is in western Turkey, even though it is not exactly a seafront city. However, it shares crucial borders with the Aegean Sea via the Gediz River that actually empties into the sea near the city of Söke. Manisa is located in the very fertile valley of the Gediz River, with gentle hills and farmland. Its history and culture go back to ancient times. It has a rich historical heritage, having been influenced by successive civilizations such as the Lydians, Persians, Greeks, and Romans.

It is located on a gentle slope down towards the coastline. Manisa also covers quite an important distance along the course of the Gediz River in the hydrological structure of this area. Thus, its discharge into the Aegean Sea can affect its coastal waters in terms of volume and flow rates, since a lot of fresh water, sediment, and nutrient transport can occur.

Manisa is associated with traditional handicrafts, local festivals, and special kinds of food. Agriculture is a main factor in the local economy, while people were traditionally attached to the land and to the river. Without being a seaside town, its people have traditional connections with the sea through trade and fisheries carried out in coastal areas not far away.

2. What is the state of the coastal currents close to Manisa?

The coastal current state around Manisa, referring to the shoreline part of the Aegean Sea where the Gediz River flows into, depends on various reasons. Generally, wind tends to be one of the strong determinants of these currents. There are numerous winds that prevail over the Aegean Sea. During summer, it is also frequently under the action of a strong north-westerly wind, meltemi; this drives the surface waters along the coast and enables a wind-driven current, which influences the dispersal of river-borne materials, such as sediment and nutrients.

Current dynamics are also further influenced by tidal forces. Although the tides of the Aegean Sea are in nature small in comparison with some other seas, they do take part in the movement of water. The ebb and flow of tides interact with wind-driven currents and river outflow. For example, at high tide, the ocean water might press against the flowing river, yet at low tide, the current in the river may overpower those acting in the coastal waters.

Another important factor is the bathymetry of the coastal region. Seabed topography at the river mouth seems to be irregular, comprising sandbars, channels, and underwater slopes. These can lead to acceleration, deceleration, or even changes in direction within currents. If there is a sandbar near the mouth, the sediment borne by the river deposits there; a deep channel, on the other hand, can let the river water farther into the sea to make way for the local patterns of current.

Moreover, the discharge of the Gediz River is a special factor for this coastal area: the amount of water, the sediment load, and possible nutrients in the river can create density-driven currents. The freshwater from the river is less dense than the seawater, and when it reaches the sea, it can form a layer of surface - level flow that spreads along the coast, interacting with the existing wind - and tide - driven currents.

3. How to observe the coastal water flow of the area related to Manisa?

Surface Drifting Buoy Method

The surface drifting buoy method can be used to observe the surface-level coastal currents in the area. Small buoys fitted with GPS tracking devices are let into the water, either near the river mouth or along the nearby coast. While the buoys are carried by the currents, their movement is monitored over time. By analyzing the buoy's trajectory, scientists can approximate the speed and direction of the surface currents. This method has its drawbacks, however. The movement of the buoys is quite sensitive to surface winds, which can easily push them off course from the actual path of the current. It also provides information about only the surface layer of water and not the deeper - layer currents.

Anchored Ship Method

A ship anchored over a site may act as a fixed platform from which current measurements can be made. Current meters are suspended from the ship at various depths. The meters may be recording the velocity and direction of the currents at each depth, yielding a detailed vertical profile of the currents at one site. However, it is limited in the area it can cover. The data only represents the immediate vicinity of the ship, and the ship itself may interfere with the natural flow of the water.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP is a preferred method for measuring coastal currents in this area. ADCPs use sound waves to measure the velocity of water at multiple depths simultaneously. ADCPs can be deployed from ships or moored to the seabed; some are attached to buoys. Because of this, they can gather a wider range of data. They were much less affected by surface-level disturbances, like wind, thus reflecting the true current condition compared to other techniques. They can also give a three-dimensional view of the current structure in detail, including horizontal and vertical flow components.

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

The ADCPs work by applying the Doppler effect. In the process, when an ADCP current meter sends high-frequency sound waves into a body of water, these waves hit small particles in the water-like plankton, sediment, or tiny air bubbles. These particles scatter the sound waves back to the ADCP. The scattered sound waves arriving at the ADCP have a different frequency from that of the emitted waves. This frequency shift, known as the Doppler shift, is proportional to the velocity of the particles and thus the water relative to the ADCP.

Most ADCPs are multibeam transducers. Measuring the Doppler shift in each beam, the ADCP can calculate the velocity components of the water in different directions. By vector addition of these velocity components, the ADCP current profiler is able to obtain the three-dimensional velocity of the water. That will give full insight into the movement of the water in every direction, which is very crucial for the correct mapping of coastal currents.

5. What's needed for high-quality measurement of the coastal currents near Manisa?

Equipment Material Reliability

The casing material of the ADCP flow meter is one of the most important aspects to consider in the interest of making high-quality measurements in the coastal waters related to Manisa. It should be made of titanium alloy. For this reason, titanium alloy has excellent corrosion resistance, and since the equipment will be constantly exposed to the corrosive seawater,. It is able to sustain a long duration in the salinity without decaying and can, therefore, be guaranteed to give long life and reliable services to the ADCP. High strength-to-weight ratio also implies that the ADCP will stand its own against strong currents or rough seas.

Size, Weight, and Power Consumption

The ADCP meter should be small in size and light in weight. A compact design facilitates deployment in an assortment of environments; for example, it may be installed with much more ease on a small research vessel or a buoy. The smaller the size, the lesser the impact on the flow field being measured. The other critical factor is the low power consumption that would allow the ADCP to work for longer intervals without the need for frequent changes of batteries or an external source of power. This becomes particularly important if the deployment of the buoys should be for longer terms along the coastlines next to Manisa.

Cost-effectiveness

The ADCP profiler should be able to provide more cost-effectiveness to enable large-scale and comprehensive monitoring of coastal currents near Manisa. For one, an ADCP that is lower in cost means many more research institutions, environmental monitoring groups, and even local initiatives can afford such equipment. The more widespread data collection this makes possible is absolutely necessary for coming to a finer understanding of complex coastal current dynamics.

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

Based on Usage Purpose

• Shipborne ADCP: This is an ADCP mounted on a moving ship. It is ideal for conducting large-scale surveys of the currents in the coastal waters. In this way, while the ship moves along the coast, the shipborne ADCP can continuously measure the currents of the sea to provide a broad-scale view of the current patterns over a large area. This would be useful for studies during the initial research or when the changes in currents need to be studied for a wide geographical range.
• Bottom-mounted ADCP: These are placed on the seabed and utilized for long-term fixed-point monitoring. They are capable of delivering continuous data related to currents at a certain depth and location. It helps to understand local hydrodynamics, like how the currents will behave in an area near the river mouth.
• Buoyant ADCP: Attached with a floating buoy, buoyant ADCPs that can move along with the surface currents. They are well-suited for the monitoring of the surface and near - surface current patterns. It can also be used to monitor the movement of water masses in a certain area over time and this again could be helpful when studying transport and dispersion of nutrients, pollutants or marine organisms.

Based on Water Depth

• 600kHz ADCP can be used for water depths within 70m. Because of the higher frequency of the sound waves, more precise measurements are allowed in shallower waters. It could give high-resolution data on the current structure and thus may turn very helpful to distinguish small-scale changes in currents.
• A 300kHz ADCP would suit a water depth of about 110m, where there is an acceptable tradeoff between measurement range and resolution. It is better for penetrating the water column deeper than that possible by the 600kHz ADCP but can still have reasonable resolution to give accurate measurements in mid-depth coastal waters.
• It is recommended to have a 75kHz ADCP for greater depths, up to 1000m. The lower frequency of the sound waves can go deeper, though the resolution may be lower as compared to higher-frequency ADCPs. This will make it fit for measuring the currents in the deeper parts of the Aegean Sea near the area related to Manisa.

There are a number of very well-recognised ADCP brands in the market, namely Teledyne RDI, Nortek, and Sontek. However, the China Sonar PandaADCP will be the most viable option in terms of cost but also with high-quality performance. Manufactured from all-titanium alloy, it offers excellent performance and durability at a very cheap price. This is an economic class ADCP that provides great value for money. You can learn more about it on their official website: (https://china-sonar.com/).

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