How to measure the coastal currents of Amalapuram?

1. Where is Amalapuram?

Amalapuram is a town in the East Godavari district of Andhra Pradesh, India. It falls in a region full of natural beauty and rich cultural heritage.

The town is close to the coast, with the Bay of Bengal as its neighbor. The surroundings have both fertile agricultural lands and a sprinkling of water bodies. Coconut palms, stretching to the horizon and swaying gently in the breeze, and paddy fields create a picture of rural tranquility. Agriculture and fishing have been the mainstays of the local economy for as long as one can remember.

The Bay of Bengal, over there, is vast and filled with energy. Starting east from Amalapuram, the coastline covers quite a stretch of sandier beaches and estuaries. Estuaries give habitats to many marine and avian species. The Sea becomes a source of livelihood as several fishermen brave its waters day and night in their traditional sail-boats. The tides are a part of the daily life of the town, affecting fishing and boat movements in and out of the estuaries.

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

In Amalapuram, the coastal currents are driven by a suite of parameters. Among them, the monsoon winds are a major driving force. The strong winds brought in by the southwest monsoon have the capability to drive the surface currents. They also affect the mixing of the layers of water and the transportation of sediments.

Next important ones are the tides. Amalapuram near the Bay of Bengal experiences semi-diurnal tides, or in simple words, regular ebb and flow. During the spring tides, the tidal currents may be very forceful with possible influences on the transport of nutrients and the dispersion of small organisms. Lastly, there is bathymetry. Undulations of shallow areas and channels in general can channel and accelerate these coastal currents.

Besides this, the entry of fresh water from the rivers and channels of the vicinity adds to this effect. Because of mixing freshwater with seawater, its density and salinity alter; due to this fact, it can change current patterns at places.

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

The surface drifting buoy method is one of the ways of observing coastal water flow. Buoys are deployed in the water, allowed to drift by surface currents, and their positions over time are tracked-usually via satellite-based tracking systems. This method, however, can only provide information on the surface currents and may not give a full understanding of the vertical current structure.

One more variant is the moored ship method. A ship is placed in a particular area, and current-measuring instruments are dropped from it. Thus, it will be possible to measure currents at various depths. However, its disadvantage includes the influence of the hull on the local current itself, which makes the measurement data erroneous. In addition, long-term mooring is very costly and labor-intensive.

The ADCP flow meter method is more advanced and efficient. ADCPs are capable of measuring the velocity of water simultaneously at various depths. They emit sound waves and detect the Doppler shift of the reflected waves to provide a detailed profile of the current from the surface to the seabed.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of Doppler. They send pulses of sound into the water. In the water, these sound waves start to scatter from particles moving within it, such as suspended sediments or even small organisms. If the water is in motion, the frequency of the reflected sound waves will be different from the transmitted frequency due to the Doppler effect.

Its magnitude depends linearly on the water velocity. ADCPs measure this frequency shift and compute from it the speed and direction of the water current. Most ADCPs send out the sound pulses in multiple directions and thus get a three - dimensional view of the current structure within the water column.

5. What does a high - quality measurement for the Amalapuram coast need?

Reliability in measurement of the coastal currents at Amalapuram needs to be highly accurate, hence it requires equipment with reliable material, a casing that withstands seawater corrosion and the mechanical forces due to waves and currents. Compact size and light weight are desirable to allow ease of deployment and installation.

Long-term and remote measurements require low power consumption. Another important consideration for widespread application is cost-effectiveness. The casings of the ADCPs are well done in a titanium alloy. Titanium alloy is quite resistant to corrosion, is strong, and could keep integrity in this aggressive marine environment.

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

Application determines the choice of equipment. For measurements while the boat is in motion, a ship-borne ADCP current profiler will suffice. Where fixed-point measurements near the seabed are required, a bottom-mounted ADCP would be a better option. For measurement at a floating position, a buoy-mounted ADCP may be used.

In terms of frequency, for water depths up to 70m, a 600kHz ADCP is appropriate. For depths up to 110m, a 300kHz ADCP is recommended, and for deeper waters up to 1000m, a 75kHz ADCP is a good option.

There are various ADCP current meter brands available, including Teledyne RDI, Nortek, and Sontek. The China Sonar PandaADCP is a Chinese brand that stands out. It is made of all - titanium alloy, offering excellent durability and a great cost - performance ratio. You can find more information at https://china-sonar.com/.

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