How to measure Teknaf's coastal current by region

1. Where is Teknaf

Teknaf-a place located in the utmost south of Bangladesh. An upscale area beside the Bay of Bengal comprises both magnificent beaches and fishing ports along with a very handy route to Saint Martin's Island.

The local people mainly depend on fishing and a little on tourism. The marine resources are rich in all types of fish, prawns, and other shellfish around Teknaf. Fishermen rely on this for their subsistence.

2. Situation of Coastal Currents near Teknaf

Tidal Currents

The tides of the Bay of Bengal play an important role in the Teknaf coastal current. There is a great tidal range, and for that reason, there is a strong tidal current in this area. In the semi - diurnal tide, two high tides and two low tides occur in a day. The speed and direction of the tidal current may vary according to the phase of the tide and local topography.

Monsoon Influence The influence of the monsoon winds is considerable. During the southwest monsoon-from June to September-the strong winds blowing from the southwest can push the surface currents toward the coast. This can alter normal current patterns and, in extreme events, cause coastal flooding. The northeast monsoon, from November to February has the opposite effect with winds pushing the currents in the other direction.

Underwater Topography Effects

The coastal currents off Teknaf are further modified due to underwater topography. Various shoals, channels and ridges underwater could deflect a current from its course as well as speed. As an example, a shoal will force the current to decelerate as well as take a course detour, keeping in mind the physics of making water go around it.

3. Methods to Observe the Coastal Water Flow near Teknaf

Surface Drifting Buoy Method

Principle: A surface buoy is deployed into the water to observe the surface current; the movement of the buoy is followed for some period using GPS or other tracking systems.

Advantages: A very simple, inexpensive technique to provide an initial idea of surface current patterns; it may yield useful data about the general direction and speed of surface current at various times of the day and with different states of weather.

Limitations: It gives information on only the surface current. The wind and waves can considerably disturb the buoy, hence giving faulty records of the direction and speed of current. For instance, during storming or strong winds, it cannot represent the actual current.

Anchor - Boat Method

Principle: An anchored boat is utilized in the measurement of currents, and instruments are drawn out of it into the water for measuring currents at depths. Advantages, Detailed depth - wise measurements of current can be performed. By using instruments such as current meters, a better understanding of the vertical structure of the current can be obtained.

Limitations: The measurement area is limited to the fixed position of the boat. It may not be able to capture the full variability of the currents in a large coastal area. Besides, the boat is subjected to waves and tides, which could introduce errors in the measurement.

Acoustic Doppler Current Profiler (ADCP) Method

Principle: ADCPs emit acoustics into the water and from their reflected signals, measure the Doppler shift to compute the velocity at various depths in the water.

Advantages: The current profile improves in a great way, starting right from the surface to the bottom of the seabed. Since ADCPs are disturbed less by surface disturbances, therefore their operation can take place without any interference, leading to a valid picture for current structures.

How Doppler-based ADCPs Work

ADCPs work on the principle of the Doppler effect, they send high-frequency acoustic pulses into the water. The frequency of the reflected pulses changes when these pulses interact with moving water particles. In the case of moving towards the ADCP current meter, the reflected signal has a higher frequency than in the case of moving away.

The ADCP current profiler instrument is mounted with several transducers, which send and receive signals at different angles. By analyzing the Doppler shifts from different directions and at different depths, this device is able to calculate three-dimensional velocity in water. That means this device will be able to determine horizontal and vertical components of velocity, therefore providing quite a detailed insight into the current structure and behavior.

4. Requirements for High - Quality Measurement of Coastal Currents near Teknaf

Equipment Materials

The equipment for high-quality measurement of the coastal currents near Teknaf should be made of reliable materials. The marine environment consists of saltwater, probable exposure to storms especially during the monsoon season, and tide and ocean current influences; therefore, there should be a durable casing. The size should be small in order to minimize deployment and retrieval tasks, mainly because sea conditions can at times be rough, and it will have beaches and other different kinds of coastal structures.

Design Considerations

The ADCP flow meter case should be lightweight for the ease of handling by personnel during installation and maintenance. Low power consumption is necessary to sustain long - term autonomous operations. Cost - effectiveness allows making large - scale measurements at an affordable price, keeping in mind the local economic and resource constraints.

Casing Material for ADCPs

For maximum performance, the casing in ADCPs is preferably manufactured using such materials as titanium alloy or high-grade stainless steel because it has excellent corrosion resistance and, therefore, can handle corrosive seawater. Their strength and durability hold well against the pressure of water in different depths. Their light weightedness-especially the titanium alloy-makes them more applicable with various deployment methods.

5. How to Select Appropriate Equipment to Measure Currents around Teknaf

Purpose-Based Selection

The first step is the purpose for which measurement of currents near Teknaf will be done. Measurements can be done either in navigation vessels or research for any short period for surface conditions as to be conducted for the local fishing boats. Either a ship-mounted ADCP profiler will suffice, or a simple surface drifting buoy system may be adequate. The former system would provide real-time current information during the voyage while the latter can give an idea about the surface current in general.

Seabed-related measurements: For measurements near the seabed, such as in the case of sediment transport, which is of great interest here because of the sandy beaches and possible coastal erosion, or for benthic ecology, a bottom-mounted ADCP meter is preferable since it can capture the details of the near-bottom current, which is so important for understanding the movement of sediment and its impact on the seabed and the beach.

Long-Term and Wide-Area Monitoring: For long-term and wide-area monitoring of coastal currents, an ADCP flow meter can be mounted on a buoy type as it can provide continuous data for a considerable period for a large area. This may be quite helpful in establishing gross patterns and variability in coastal currents.

Frequency Consideration for ADCPs

In the case of ADCP current profiler frequency, for water depths up to 70m, which is relevant for much of the coastal area near Teknaf, a 600kHz ADCP will suffice. For deeper waters that may be found in some offshore areas or in channels, a 300kHz ADCP or lower (depending on the depth) can be more appropriate, and for deeper waters, as may be encountered near Tomakomai, greater than 1000m for instance, a 75kHz ADCP would be most suitable. The choice of frequency also depends on the specific requirements of the measurement, such as the level of detail needed for the current profile and the tradeoff between accuracy and range.

There are well-known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also worth considering. It is made of all-titanium alloy material and offers an excellent cost-performance ratio. You can find more information on their website: https://china-sonar.com/.

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