How can we measure the coastal currents of Basrah?

1. Where is Basrah?

Basrah is one of the major cities in the south of Iraq, close to the junction of Shatt al - Arab River and the Persian Gulf. It is a highly historic and economically important city.

Geographically, most parts of Basrah are surrounded by a flat marshy landscape. The Shatt al - Arab River, formed by the confluence of the Tigris and Euphrates rivers, is an important waterway for transportation and trade. Its connection to the Persian Gulf is a key factor in its maritime activities.

The people of Basrah have had a long-standing relationship with the water. The economy in this area has mainly been based on fishing and trade for many centuries. The main features of the coastal area in the north of Basrah, adjacent to the Persian Gulf, include a muddy shoreline with large sections of tidal flats, plus some sandy beaches; in several places, waters are pretty shallow and also contain many nutrients because of river inflow. This makes it a productive area for fishing and thus a host for many fish species, shrimps, and mollusks of different kinds.

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

The coastal currents around Basrah are influenced by many forces. The tidal currents play the major role. Tidal activity in the Persian Gulf is due to the pulling power of the moon and the sun. This acts to create a regular rising and falling of the water level. The Shatt al - Arab River comes into play, as well. The outfall of fresh water from the river out into the gulf has the potential to create complicated current effects. The interaction between the river current and the tidal current can lead to the formation of eddies and areas of mixing.

Also very relevant are the wind-driven currents. The general circulation winds of the area may push the surface waters and generate surface currents. The direction and strength of those winds can be seasonal and therefore so will be the coastal circulation. For instance, during the summer months, the pattern may be different than in winter and the current directions and speeds also change.

The topography of the bottom off Basrah further influences the currents: shallow areas such as tidal flats and deeper channels may act as a kind of bypass and hence deflect and change the direction of flow. The morphological form of the coastline in conjunction with the underwater topography forms a specific current regime.

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

Surface Drift Buoy Method: In this, buoys are dropped on the water surface and left to drift with currents. Such buoys are normally equipped with a tracking device such as GPS. The buoy movement is then monitored over time, determining the direction and speed of the surface currents. This method provides information related only to the surface layer, or any detailed information about the vertical structure of the currents.

Anchor Ship Method: This involves anchoring the ship in certain selected locations near the coastal area of Basrah, with instruments such as a current meter installed on it to detect the flow of water at that particular spot. The disadvantage with this, however, is that as much as it may be quite workable for areas surrounding the immediate vicinity, it may fall short regarding coverage of large areas or depths simultaneously.

Acoustic Doppler Current Profiler (ADCP) is an advanced and further efficient way of measurement of the coastal currents. The technique measures the velocity at different depths within the water column, using the Doppler effect, sending acoustic pulses into the water and measuring the frequency shift in the reflected signals from the moving water particles. Hence, this allows a detailed understanding of the vertical profile from the surface to the seabed.

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

ADCPs work on the principle of Doppler. Transducers on an ADCP current meter emit acoustic pulses into the water. Due to the Doppler effect, when these sound waves reflect off moving water particles, a frequency shift occurs in the reflected waves. The frequency shift is proportional to the velocity of the water particles relative to the ADCP profiler.

ADCPs usually have multiple transducers that measure water velocity in different directions. The ADCP current profiler can then calculate the three-dimensional velocity of the water in the east-west, north-south, and vertical directions by emitting pulses in different directions and analyzing frequency shifts of the reflected signals. Also, the time taken by sound waves to travel from the transducer to the water particles and back is measured. These data, in conjunction with the frequency shift, are used to calculate with high precision the speed and direction of flow of the current at various depths.

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

For high-quality measurements of coastal currents around Basrah, definite features are in need for such equipment. This equipment should first be made with appropriate material to bear harsh marine conditions. The device should have a small size and light weight so that it will be easily deployed and handed. In addition, low power consumption is required since continuous operation must be achieved; especially in cases of long-term monitoring.

The casing of the ADCP flow meter is preferably made of titanium alloy. Titanium alloy has excellent corrosion-resistant properties, something important in the saline environment of the Persian Gulf. Besides this, it has a high strength-to-weight ratio, which means that it is strong enough to be durable while keeping the equipment relatively light. This material will be able to withstand pressure changes associated with different water depths.

6. Selection of Equipment for Current Measurement?

While selecting the equipment at Basrah for current measurement, consider the following factors.

Type of ADCPs can be chosen based on the purpose of use. For example, the ship-borne ADCP installed on a vessel can measure currents during the movement of the ship itself; this is useful to map a wide area of the coastal waters. A bottom-mounted ADCP is fixed on the seabed and provides stable measurements of the currents passing above. It is ideal for long-term monitoring at a specific location. A buoy-mounted ADCP combines the best features of mobility and ease of deployment, enabling measurements in different areas.

Regarding the ADCP frequency, it needs to be depth-dependent. For instance, in water as shallow as 70m or less, a 600kHz ADCP is considered ideal because it gives very high-resolution data in shallow water conditions. In the case of depths up to 110m, a 300kHz ADCP can be utilized. For deeper water, such as near 1000m, a lower frequency, like 75kHz, is recommended to allow for the measurement of accurate data over a large vertical extent.

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.