How do we go about measuring the coastal currents in Hub?

1. Where is Hub?

It lies in the province of Balochistan in Pakistan on the Arabian Sea coast, and it has been found to be a very prospective area with the increase of trade and other maritime ventures:.

It has an interesting and varied population involved in the fishing, port-related, and other coastal-based industry. It is a centre with combined traditions because of the multiple value systems and religious lessons. The beaches, flats, and areas around Hub are made up of the estuary and mangrove forests of the sandy shores.

Lying close to the Arabian Sea is a source of importance. A great variety of marine life, ranging from a large number of fish species to prawns and mollusks, inhabits these waters along the coast. It provides a major transportation route, with ships transporting goods to and from the port of Hub. The tides have a great influence on the local coastal environment, which dictates the flow of water and sediment distribution, affecting the health of the coastal ecosystems like the mangroves.

2. What is the situation surrounding the coastal currents around Hub?

A number of factors influence the coastal currents in the vicinity of Hub. Among these, tidal currents represent one of the main controls. The tides-the result of the gravitational pull of the moon and sun-have their related tidal currents changing in strength and sometimes in direction. Topography and shape of coastline, including submarine features, play important roles in changing flow near Hub. These are: sandbars, channels, and shoals that divert or change the flow of water.

The effect of monsoon winds is enormous. The southwest monsoon from June to September gives strong winds that can act as a driving force on the surface waters. Such winds, affecting the direction and speed of the coastal currents, easily result in a different type of current pattern. Further, the freshwater inflows from the nearby rivers mix with seawater, which modifies the salinity and density-driven currents.

Moreover, the wide-scale ocean circulation patterns of the Arabian Sea can also interact with the local coastal currents. Inflow can allow different water masses from other areas to come in and produce changes in temperature, salinity, and overall characteristics of coastal currents.

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

Surface Drift Buoy Method: The method prepares buoys to be dispersed on the water surface. These buoys are designed to drift with the currents. By using satellite-based tracking systems or other positioning methods to monitor the movement of the buoys over time, we can obtain information about the direction and speed of the surface currents. However, this method mainly provides data for the surface layer and may not give a comprehensive understanding of the currents at different depths.

Anchor Boat Method: This is done by taking a boat, anchoring it in the coastal waters, and undertaking the measurement of the flow at different depths around the boat by the use of instruments. The exact details for the area that covers the immediate surroundings from where the measurements are actually undertaken can be obtained; though quite cumbersome and lengthy processes, there are further drawbacks with regard to area covering in this method as well.

The Acoustic Doppler Current Profiler(ADCP) technique represents one of the modern and more efficient methods for the measurement of currents near the coast. It makes use of sound waves for water-velocity measurement at more simultaneous depths. It sends out sound pulses and then measures the Doppler-shifted reflections from particles in the water, hence offering a very detailed profile of the current from the surface to a specific depth. This gives a more accurate and complete picture of the currents in the coastal area than is obtained with the other methods.

4. How Do ADCPs Using the Doppler Principle Work?

Basically, ADCPs are based on the Doppler effect. They send out sound pulses into the water. These sound waves interfere with the particles in the water-sediment particles, plankton, or any other small organism-the frequency of the reflected sound waves changes due to the Doppler effect. If the particles are moving towards the ADCP, the frequency of the reflected waves would be higher than the emitted waves, while if the particles are moving away, then the frequency is lower.

This unit works out the water's speed in various directions through the changes in frequency of the reflected sound waves while their angle and depth are changing. The ADCP sends and receives these sound signals with several transducers, which enable the device to create a fairly detailed profile of the velocity of water through the column of water, from the surface down to some instrument-specific depth.

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

The equipment to be used for high-quality measurement of the coastal currents near Hub should be made of reliable materials. The marine environment is so harsh, with salt-water corrosion, temperature fluctuations, and even the possibility of physical impacts from floating debris; the equipment needs to be durable.

The equipment used should be of small size, for it is easy to deploy and install. Whether at the seabed, buoys, or boats, small equipment makes it easy to handle during installation. It also makes the process of transportation and maintenance quite convenient.

Lightness in weight, especially in floating or moored devices, will be required so that the buoyancy is not affected and stability may be ensured. Low power consumption is also important, as this allows the device to operate continuously over a long period without frequent replacement of batteries or a large power supply.

Another very important point is cost-effectiveness. In order to make large-scale measurements along the coast, the equipment should not be too expensive. Regarding ADCPs, one of the best options is casing made from titanium alloy. Such an alloy has very good resistance to corrosion, which is very important in a salty marine environment. Besides being resistant to corrosion, the alloy is strong yet rather light, which also corresponds to all the requirements of the highest-quality current-measurement equipment.

6. How to select appropriate equipment for current measurement?

While selecting the equipment for the measurement of current at a place near Hub, first of all, the purpose of its use has to be ascertained.

Ship - borne ADCP: This is suitable for measurement from a moving vessel: It records the coastal currents continuously while the ship is moving along the coast. A series of data points can thus be obtained over the relatively wide area covered by the route followed by the ship.

Bottom-mounted ADCP: This is most suitable for fixed-point measurements at the seabed. This yields a steady and long record of the water flow near the bottom, which is highly necessary to understand the interaction between the bottom topography and the coastal currents.

ADCP buoy-mounted: It is done in the case when measurements are to be made in one particular area for longer duration while floating at the water surface. It can be deployed at points of interest and provide data continuously without keeping a vessel all the time.

For the waters within 70m, a 600kHz ADCP will be appropriate, in terms of frequency. When it relates to water up to 110m, the recommended should be a 300kHz ADCP. When dealing with deep waters of up to 1000m, a 75kHz ADCP will do the work.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also worth mentioning. It has a casing made entirely of titanium alloy and offers an excellent cost - performance ratio. You can find more information about it at https://china-sonar.com/.

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