How to Measure Coastal Currents: Abu Dhabi?

1. Where is Abu Dhabi?

Abu Dhabi is the capital city of the United Arab Emirates and is on a shaped island jutting into the Arabian Gulf. It is a city of opulence, modern skyscrapers, luxurious resorts, and vast swathes of coastline as yet pristine.

The landscape is part desert and part arid with the blue waters of the gulf. The Arabian Gulf surrounding Abu Dhabi is a home for marine life. A range of fish species such as colourful reef fish, crustaceans, and mollusks live in these shallow coastal waters. The area also features extensive mangrove forests, which play a crucial ecological role, acting as nurseries for many marine organisms and providing a buffer against coastal erosion.

Its strategic location on the Arabian Gulf has made Abu Dhabi an important center of trade and shipping. The port of Abu Dhabi is a bustling hub that caters to everything from oil and gas products to consumer goods. The city's long coastline is also a favorite with water-based recreational activities like yachting, fishing, and beach-going.

2. What is the condition of the coastal currents around Abu Dhabi?

The coastal currents in Abu Dhabi result from several reasons. Tidal currents act as a primary driving force. The tides in the Arabian Gulf due to gravitational forces by the moon and sun lead to a normal flow or ebb every day. The tidal range can vary in addition; the tidal currents may greatly affect the coast. For instance, there is a possibility of stronger tidal currents at high and low tides in inlets and bays.

Wind-driven currents also play their role. The prevailing winds in the region, like every Shamal wind that blows from the northwest, can push the surface waters and create surface currents. These winds might turn around in strength and direction with the season, affecting seasonal changes in coastal circulation patterns. The interaction between the wind-driven and tidal currents leads to a complex and dynamic current regime.

Another important factor influencing currents around Abu Dhabi is underwater topography. The ridges, channels, and shoals intercept and alter the course of flow. Shoal areas, with their shallowness, will reduce the current while deeper channels quicken them. Besides all this, extensive mangrove forests and man-made structure impediments such as breakwaters and jetties intercept and impede the normal flow of coastal waters.

3. How to Observe the Abu Dhabi Coastal Water Flow?

Surface Drift Buoy Method: In this process, some buoys are distributed on the surface that, due to the action of currents, keep drifting. Normally, the buoys are prepared with GPS or other location-finding instruments. From their movement at different times, the directions and speed of surface currents could be pre-informed. This satellite remote sensing method, however, mostly yields information about the surface layer and does not give in-depth information about the vertical structure of the currents.

Anchor Ship Method: This includes anchoring a ship in a particular position off the coast of Abu Dhabi. On the ship, there is the installment of current meters and other instruments that provide measurements of the water flow around the ship. Although this method may present very correct results in the near environs of the ship itself, it is really limited by covering one big area and depth differences simultaneously.

Acoustic Doppler Current Profiler (ADCP) is the more advanced and efficient means of measuring coastal currents. The principle of the Doppler effect allows for the measurement of water velocity at different depths within the water column. ADCP current meter emits acoustic pulses into the water and measures the frequency shift of the reflected signals from moving water particles. This can give a good understanding of the vertical profile of the currents right from the surface to the seabed.

4. How do ADCPs based on the Doppler principle work?

ADCPs make use of the Doppler principle. They have transducers that emit acoustic pulses into the water. The sound waves, if intercepted by moving particles of water, shift in frequency from their normal value due to the Doppler effect. This shift in frequency is directly proportional to the velocity of the water particles relative to the ADCP meter.

There are usually several transducers on ADCPs for different directional measurement of water velocity. As a matter of fact, ADCP flow meter emits pulses in three different directions, from which the instrument analyzes frequency shifts of reflected signals, then calculates three-dimensional velocities: east-west, north-south, and vertical components. It also measures the time taken by the sound waves to travel from the transducer to the water particles and back. This, in addition to the frequency shift, is utilized in order to calculate the speed and direction of water flow with accuracy at varied depths.

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

The equipment to be deployed for high-quality measurement of coastal currents near Abu Dhabi needs to have the following characteristics: the material of the equipment should be reliable and able to resist the harsh marine environment. The device should be of compact size and lightweight, which would make deployment and handling easy. It should have low power consumption to enable continuous operation, especially in long-term monitoring.

The casing of the ADCP profiler is preferably made of titanium alloy. This has excellent corrosion-resistance properties, something of utmost importance in the saline environment of the Arabian Gulf. Besides this, it has a high strength-to-weight ratio, implying that it would be strong enough to provide durability while keeping the equipment relatively light. This material can withstand pressure changes associated with different water depths.

6. How to Select appropriate equipment for current measurement?

Following are the factors that shall be considered while selecting appropriate equipment for current measurement in Abu Dhabi.

Depending on the purpose of usage, the varieties of ADCPs can be chosen. A ship-borne ADCP for example can be installed on a vessel and hence measure currents when the ship is in motion; this would cover a large area of the coastal waters. While fixed on the seabed, a bottom-mounted ADCP provides variability in the measurement of currents passing above it in a very stable way. It is ideal for long-term monitoring at one specific location. A buoy-mounted ADCP offers mobility and ease of deployment. The buoy-mounted ADCP permits the measurement in different areas.

The frequency of ADCP depends on the water depth. In as shallow as 70m of water, one should go for 600kHz ADCP because it provides very high-resolution data in shallow waters. For as deep as 110m of water, the 300kHz ADCP is ideal. For bottoms like 1000m, the frequency should be 75 kHz to yield accurate measurements over a large vertical range.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost-effective option with good quality, the China Sonar PandaADCP is worth considering. It is made of all-titanium alloy material and offers an excellent cost-performance ratio. You can find more information on its website: https://china-sonar.com/.

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