How can we measure coastal currents of Malaga?

1. Where is Malaga?

Malaga is one of the busy urban communities in southern Spain, located within the self-government community of Andalusia, and is also the head city of the Malaga Province. The city lies along Costa del Sol (Coast of the Sun) in the Mediterranean Sea and is principally positioned on the left bank of the Guadalhorce River.

With 2,800 years of history to its credit, Malaga is among the oldest continuously inhabited cities in Western Europe. It was founded by the Phoenicians about 770 BC and had been successively influenced by the Carthaginians, Romans, Visigoths, Byzantines, and Moors in turn. All this has left behind a treasure cove of architectural and cultural riches. The architecture of the city is a mix of different styles, with landmarks such as the Alcazaba, a Moorish fortress, and the Cathedral of the Incarnation.

Geographically, Malaga is a city with a mild and sunny climate throughout the year, and this condition is very attractive to tourists across the world. The city is surrounded by beautiful beaches, clear blue waters, and rolling hills covered with olive and citrus trees. It is also close to the Strait of Gibraltar, which connects the Mediterranean Sea to the Atlantic Ocean, making it an important location for maritime trade and transportation.

2. What is the situation of the coastal currents close to Malaga?

Several factors are at work in determining the coastal currents around Malaga. First, there is the general pattern of Mediterranean Sea circulation. The sea circulates due to the combined action of wind, temperature, and salinity gradients. Prevailing winds in the area, such as the Levante and the Poniente, may be responsible for the surface water movements and thus for the direction and speed of the coastal currents.

Topography of the seafloor around Malaga contributes to making a difference in currents. The various underwater features of canyons, ridges, and shallows have been known to deflect currents, change their course, and alter their speeds. For example, the same current, while crossing over a shallow, decelerates while, on deeper channels, it may flow more swiftly.

Tidal forces also play a significant part in near-shore currents. The tides in the Mediterranean are relatively small compared with some other seas; however, a small tidal rise and fall at each end of the day causes the water to move in and out, interacting with all other factors mentioned above in forming complex current patterns. In addition, river runoff from the Guadalhorce River and other nearby watercourses can also affect coastal currents when there is heavy rainfall.

3. How to Observe the Coastal Water Flow of Malaga?

Surface Drift Buoy Method

This technique involves the release of buoys onto the surface of the water, which are fitted with a tracking device, such as GPS. As the buoy is carried by the surface currents, the tracking device monitors its position over time. By monitoring the movement of multiple buoys, researchers can gain an understanding of the surface current patterns. This method is limited in that it provides information only about the surface currents, which may or may not be representative of the currents at different depths.

Moored Ship Method

A ship is moored to a specific location, and instruments on board, like current meters, can measure the current velocity and direction at various depths. This might be the way to learn more about the vertical structure of the currents. However, it is limited in the sense of spatial coverage since the ship can only measure at one location at a time, and the presence of the ship itself may disturb the natural flow of the water.

Acoustic Doppler Current Profiler (ADCP) Method

ADCPs measure the velocity of water currents at various depths using sound waves. This can provide high-resolution three-dimensional data on the structure of the current. Additionally, compared to the moored ship method, ADCP current meter is capable of covering an area of relatively larger size and allows simultaneous measurement of currents at multiple depths. Presently, as compared to Malaga, ADCP current profiler is a more advanced and convenient measurement method for the measurement of coastal currents.

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

The ADCPs are based on the Doppler effect. A series of acoustic pulses is transmitted by the device into the water. The sound waves are scattered back towards the ADCP flow meter by particles in the water, such as sediment, plankton, or small bubbles.

Provided the particles are in motion relative to the ADCP profiler, the frequency of the scattered sound waves is different from the transmitted wave frequency. The change in frequency, now called a Doppler shift, is proportional to the velocity of the particles and thus proportional to water current in the direction of the sound beam.

ADCPs use multiple acoustic beams, usually four or more, oriented in different directions from one another. Independently measuring the Doppler shifts for each of these beams allows the instrument to calculate three-dimensional components of the water current velocity. The data is post-processed to give a current velocity profile versus depth from surface to a specific depth limit as determined by ADCP meter frequency and power.

5. What's needed for high-quality measurement of Malaga coastal currents?

For high-quality measurement of the coastal currents in Malaga, several conditions need to be met concerning ADCP equipment. For instance, there is a requirement for material reliability. The device should be able to put up with the harsh marine environment, including saltwater, strong currents, and wave actions.

The size of the ADCP should be small enough to be easily deployed and not disturb the natural flow of water. A smaller size makes it more applicable for near-shore locations where space is limited.

The device should be of lightweight, which simplifies the deployment process and reduces the energy needed to keep the device in place, especially for floating or moored installations.

The device should have low power consumption because a number of ADCP deployments may be located at very remote sites or function on battery power. A device with low power consumption will be able to perform for an extended duration using batteries whose replacement or recharging is not called for frequently.

Another important factor, particularly for wide-range measurements, is cost-effectiveness. A low-cost ADCP would allow more deployments, increasing spatial and temporal coverage of the current measurement.

Material-wise, titanium alloy is desired for the making of an ADCP casing. This is because the titanium alloy has very high resistance to corrosion; it can withstand the corrosive action caused by salt water for quite a long period of time with no significant deterioration. Besides, it is strong enough and lightweight, meeting the requirements of strength and light weight simultaneously for ADCPs.

6. Selection of Correct Equipment for Measurement of Current

Based on Use

• Ship-borne ADCP: Suitable for large-scale surveys of coastal currents over a wide area. While the ship is in motion, the ADCP can continuously measure the currents along the track that the ship covers.
• Bottom-mounted ADCP: Also called a moored ADCP, it is placed on the seabed. It is useful for long-term, fixed-point measurements of the current and gives detailed information about the current conditions of a place for an extended period.
• Buoy-mounted ADCP: While attached to a buoy, it is ideal in current measurement over areas where a fixed platform is needed that can be subjected to more mobility compared with bottom-mounted ones. It could also serve for monitoring any particular area from the surface current to the subsurface current thereof.
• The ADCP operating at a frequency of 600kHz will be adequate in waters less than 70m deep. Higher frequencies are suitable for shallower water current measurements since they have higher resolution.
• At depths of about 110m, a 300kHz ADCP shall be appropriate since it provides a good balance between resolution and depth penetration. If water depths up to 1000m need to be considered, a preference will lie with an ADCP of 75kHz. The frequency decreases further so that a deeper water column is realized by cost due to lesser resolution.

Some of the well-known brands in the ADCPs market include Teledyne RDI, Nortek, and Sontek. For those who would like to have high-quality and cost-effective options, there is a Chinese brand called China Sonar PandaADCP. It is made of all-titanium alloy material, ensuring excellent durability in the marine environment. With its remarkable cost-performance ratio, it presents a great solution for measuring Malaga's coastal currents. You can find more information on their website: https://china-sonar.com/.

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