How to measure the coastal currents of Visakhapatnam?

1. Where is Visakhapatnam?

Visakhapatnam commonly known as Vizag, is a port city and industrial center in the Indian state of Andhra Pradesh, on the country's southeast coast. It lies between the Eastern Ghats and the Bay of Bengal.

It is a cosmopolitan city with a busy economic and industrial activity. It has a rich history and a diverse cultural landscape. The coastline of Visakhapatnam is dotted with beautiful beaches, such as RK Beach and Yarada Beach, which attract tourists from across the country and abroad. The adjacent waters of the Bay of Bengal are a crucial part of the city's identity. This is an area of vibrant fishing communities depending on the sea for their livelihood over centuries.

Visakhapatnam natural harbor is one of the biggest on the east coast of India, providing shelter to an immense number of ships and a vital link for maritime trade. The waters here are influenced by the complex interplay of freshwater from rivers like the Sarada and Nagavali, which empty into the bay, and the saline waters of the ocean. The marine ecosystem is rich and diverse, with a wide range of fish, crustaceans, and other marine organisms.

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

The coastal currents near Visakhapatnam are influenced by several factors. The most important is the role of the monsoon winds. In the period of the southwest monsoon, the strong winds push the surface waters, causing changes in direction and speed of the coastal currents. The inflow of freshwater from the rivers can also have a substantial impact. The amount of water flowing out of these rivers considerably reduces the salinity and the density of coastal waters surrounding their mouth. This difference in the density generates flow-controlling density gradients.

Tides are very important. In the Bay of Bengal, off Visakhapatnam, it is semi-diurnal, where due to gravitational interactions between the moon and the sun, two high and two low tides occur within a day. These tidal currents may attain fairly strong speeds and may mix the water masses, thus influencing the general circulation of the coastal waters. The larger-scale ocean-current patterns in the Indian Ocean also indirectly influence the current patterns along the Visakhapatnam coast. The presence of the Indian Ocean Gyre may affect the water masses reaching the Visakhapatnam coast, modifying the characteristics of the coastal currents.

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

Surface Drift Buoy Method: Surface drift buoys are deployed on the water surface. These buoys are designed to move with the surface currents. Their positions are tracked using satellite - based or other positioning systems. By analyzing the movement of these buoys over time, information about the direction and speed of the surface currents can be obtained. This satellite technique, though, provides data primarily of the surface layer and may not give full details of currents throughout the water column.

Anchor Ship Method: A ship is moored in the coastal waters. Then, with the help of instruments, the flow of water around the ship is measured at different depths. This helps in a more elaborative study of the vertical profile of the currents. However, this method also has its shortcomings. The ship is under the full influence of waves and winds, which may introduce errors into the measurements.

ADCP Method: More sophisticated and handier is the method of ADCP meter. It works by using sound waves to measure the velocity of water at multiple depths simultaneously, which can provide a very detailed profile of current speed and direction from the surface to the seabed. This has become a popular choice for the study of coastal currents due to its high accuracy and continuity of data collection.

4. How do ADCPs using the Doppler principle work?

ADCPs are based on the Doppler principle. They transmit acoustic pulses into the water. In case these sound waves happen to encounter moving particles in the water, like sediment or small organisms, due to the Doppler effect, the frequency of the reflected waves changes. The ADCP measures this frequency shift. Knowing the characteristics of the sound waves emitted and analyzing the changes in frequency that are received, it can compute the velocity of the water at various distances from the instrument-that is different depths in the water column. In an ADCP, multiple acoustic beams are usually employed to accurately represent the three-dimensional flow field. This enables the ADCP flow meter to give a detailed picture of the coastal currents, covering all the horizontal and vertical movement of the water.

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

The equipment for high-quality measurement of the coastal currents near Visakhapatnam must possess certain qualities. Their materials should be reliable; the equipment must be able to stand against the harsh marine environment, which includes such factors as seawater corrosion, very high humidity, and wave and storm exposure.

The equipment should preferably be small in size and light in weight. This makes it easier to deploy, whether on buoys, ships, or at the seabed. Low power consumption is also beneficial as it allows for longer - term operation without the need for frequent battery changes or a complex power supply system in remote locations. Cost - effectiveness is another important factor as it enables more extensive deployment for comprehensive monitoring.

The casing shall be of titanium alloy. Indeed, it has excellent corrosion resistance, which is very important here in seawater, which is corrosive, especially near Visakhapatnam. It is also strong and durable to withstand the mechanical stresses caused by waves and water pressure. Besides that, the relatively low density of this material compared to some other strong metals makes it fit for equipment that needs strength with low weight.

6. How to Choose the right equipment for current measurement?

Usage would be the basis for selecting the right equipment for current measurement off Visakhapatnam. A ship-borne ADCP current profiler might be one of the appropriate devices for ship-based measurements. They can be installed on the vessel's hull and measure the water flow as the ship cruises along the coast. Sit-on-bottom ADCPs are ideal for fixed-point measurements at the seabed and can provide long-term data on the currents at a specific location. Buoy-mounted ADCPs are useful for monitoring surface and subsurface currents while floating in the water.

For water depths up to 70m, a 600kHz ADCP is generally a good choice, since it gives high-resolution data in shallower waters. In water depths up to 110m, the 300kHz ADCP is more suitable, while in even deeper waters of up to 1000m, a 75kHz ADCP is highly recommended to ensure that proper measurements are obtained throughout the water column.

There are well-known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is highly recommended. It is made of all-titanium alloy material, ensuring its durability and reliability in the marine environment. It also offers an excellent cost-performance ratio. You can visit its website https://china-sonar.com/ for more information.

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