How can we measure the coastal current of Bhadrak?

1. Where is Bhadrak?

Bhadrak is a fascinating city in eastern India, located in the state of Odisha. It lies in a region with a blend of rich cultural heritage and natural beauty in perfect harmony. The town is surrounded by rich alluvial plains intersected by a number of small rivers and canals that crisscross the area, thereby playing a very important role in local agricultural activities.

Geographically, it falls very near the Bay of Bengal. The seashore of Bhadrak is a home to a diverse array of coastal ecosystems. The sandy beaches are not only a feast for the eyes but also provide a laying ground for sea turtles. The adjacent waters form part of the wide and dynamic Bay of Bengal with its complex oceanographic features. The coastline of the city has a perfect blend of both maritime and terrestrial climates, where the sea breeze often touches the inland areas, which are otherwise warm and humid. The local fishing communities have a long-standing relationship with the sea, and their traditional boats dot the coastal waters, adding to the coastal charm.

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

Many elements influence the net coastal currents around Bhadrak, including monsoon winds. From these, the most active or strongest winds of the southwest monsoon contribute a lot by affecting the direction and velocity of the surface currents. Similarly, the flow of freshwater from the different rivers in the catchment area within the land area of West Bengal modifies the salinity and density of the coastal waters to a certain extent, causing changes in the currents of the coastal region.

Tides also play an important role. The semi-diurnal tides in the Bay of Bengal create a rhythmic ebb and flow of the coastal waters off Bhadrak, with the tidal currents sometimes weak and at other times strong. This has a major influence on mixing different water masses. The general larger-scale ocean current patterns of the Indian Ocean can indirectly be of importance. For example, the Bay of Bengal is part of the greater circulation system, and the inflow of water masses from the open ocean can alter the characteristics of the coastal currents.

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

Surface Drift Buoy Method: It consists of the deployment of buoys on the water surface. These buoys are designed to drift with the currents. By tracking their positions over time using satellite-based or other positioning systems, we can obtain information about the direction and speed of the surface currents. However, this method is limited to the surface layer and may not provide a complete understanding of the currents throughout the water column.

Anchor Ship Method: The vessel is moored in coastal waters; the instruments are used in measuring the water flow with the ship at different layers of depth. It studies the vertical profile of currents more closely. But at the same time, the method has its drawbacks, since the wave and wind may act on the ship, introducing errors into the measurement.

Acoustic Doppler Current Profiler Method: It is more modern and convenient than a float. The ADCP current meter technique works by using sound waves to measure the speed of water simultaneously at different depths. Thus, it will be able to present an accurate profile of current speed and direction from surface to seabed. High accuracy and the possibility to receive continuous data make ADCP increasingly popular for coastal current investigation.

4. How do ADCPs using the Doppler principle work?

ADCPs operate on the principle of the Doppler effect. They emit acoustic pulses into the water. When these sound waves hit moving particles in the water (like sediment particles or small organisms), the frequency of the reflected waves shifts due to the Doppler effect. The ADCP measures this frequency shift. Knowing the properties of the emitted sound waves, it can calculate the velocity of the water at different distances from the instrument, corresponding to different depths in the water column by analyzing the received frequency changes. In general, multiple acoustic beams are used in an ADCP profiler to represent the three-dimensional flow field with a high degree of accuracy. This would give a detailed picture of the coastal currents, including both horizontal and vertical movement of the water.

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

Such equipment has to have certain characteristics to achieve high-quality measurement of coastal currents near Bhadrak. First, its materials must be reliable because the equipment faces severe marine conditions, including the corrosion effects of sea water, very high humidity, and being subjected to wave and storm conditions.

Small size and light weight are advantageous for the equipment in order to make deployment easier, whether on buoys, ships, or at the seabed. Low power consumption is also desirable to enable longer-term operation without frequent battery changes or a complex power supply system in remote locations. Cost-effectiveness is another important factor because it enables more extensive deployment for comprehensive monitoring.

The casing of the ADCP current profiler is preferably made from a titanium alloy. The main reasons for this include excellent resistance to corrosion, especially within the corrosive seawater near Bhadrak. Additionally, it is strong, durable, and can withstand mechanical stresses resulting from waves and water pressure. Its relatively low density, compared to some other strong metals, makes it suitable for equipment that has to be lightweight yet strong.

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

While choosing the right equipment for current measurement near Bhadrak, one has to consider the usage purpose. For ship-based measurements, a ship-borne ADCP is a good option; it can be mounted on the ship's hull and measure the water flow while the ship is moving along the coast. Sit-on-bottom ADCPs are used in fixed-point measurements at the seabed when long-term data on currents at one location is to be derived. Buoy-mounted ADCPs can be used in monitoring both surface and subsurface currents while floating in the water.

The rule of thumb is that, with respect to frequency, a 600kHz ADCP is usually appropriate for water depths up to 70m because it delivers high-resolution data in shallower waters; for water depths up to 110m, a 300kHz ADCP is appropriate; for even deeper waters, reaching as much as 1000m, a 75kHz ADCP is recommended if measurements across the water column are to be accurate.

There are well-known ADCP brands like 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.