Measuring the Coastal Currents of Kuakata

1. Location and Description of Kuakata

Kuakata sea beach is situated in Bangladesh. It faces the southernmost part of the country overlooking the Bay of Bengal. It is a favorite tourist destination because it offers unique sunrise and sunset views over the sea.

The local economy is based on fishing and tourism. The Bay of Bengal near Kuakata is rich in marine resources, including a variety of fish, prawns, and other shellfish. Fishing is a major livelihood for the local people, and the tourism industry is growing due to the natural beauty of the area.

2. The Situation of Coastal Currents near Kuakata

Tidal Currents

The tides of the Bay of Bengal play a great role in the coastal currents at Kuakata. The tides are semi-diurnal, with two high tides and two low tides in a day. The tidal range can be very large, and these tidal currents can vary in strength and direction. Due to the rise and fall of the tides, the current pattern is quite complicated, affecting the local marine environment and fishing activities.

Monsoon Influence

The coastal currents are closely related to the monsoon winds. During the southwest monsoon, strong winds blow from the southwest towards the coast between June and September. Such winds can cause surface currents to result in apparent changes in the regular current pattern. The northeast monsoon influences them during the months of November to February, where winds from the northeast influence the directions and speeds of the currents.

Underwater Topography

The topography underwater near Kuakata affects the currents in the coast. It is possible that the existence of sandbars, shoals, and channels can change the direction and speed of the currents. For instance, a sandbar may slow down the current and split it, while a channel may funnel the current and increase its speed.

3. Methods to Observe the Coastal Water Flow near Kuakata

Surface Drifting Buoy Method

Principle: A surface-drifting buoy is released into the water to observe the surface current. The movement of a buoy is followed for sometime using GPS or other tracking systems. Advantage They are relatively easy and inexpensive as an introductory means to determine surface current patterns. Resultant data can be used to trace the direction and velocity of surface current at different times of the day and under various weather conditions.

Limitations: This can only give information about the surface current. Wind and waves may have a great effect on the buoy's movement, giving incorrect measurement of the direction and speed of the current. For instance, if there is a storm or strong winds, the buoy cannot accurately represent the actual current.

Anchor-Boat Method

Principle: An anchored boat is used for measuring the current. Instruments are lowered from the boat into the water for measuring the current at different depths. - Advantages: It allows more detail in depth-wise measurements of the current. With the help of instruments like current meters, the vertical structure of the current can be better comprehended.

Limitations: The position of the boat cannot be changed; it also limits the area of measurement. It may not give an idea about the whole range of variability of the currents within a large coastal area. Waves and tides might make a disturbance to the boat itself and provide errors in measurement.

Acoustic Doppler Current Profiler (ADCP) Method

Principle: ADCPs emit acoustic signals into the water and measure the Doppler shift of the reflected signals to calculate the velocity of water at different depths.

Advantages: This gives a better profile of the current from surface to seabed. There is less surface disturbance interference with ADCPs, and they can continuously operate for long periods, therefore providing better accuracy of the current structure.

4. How ADCPs using the Doppler principle work

Acoustic Doppler Current Profiler (ADCP) functions on the principle of the Doppler effect. The instrument emits high-frequency acoustic pulses into the water. Wherever these pulses encounter moving particles of water, the frequency of the reflected pulses alters. If the water is approaching the ADCP, then the frequency of the reflected signal is higher than the one emitted, and if they are moving away, the opposite happens.

The ADCP profiler has several transducers which emit and receive signals at varying angles. Through the analysis of different directional Doppler shifts at depth, it can calculate the three-dimensional water velocity. That is to say, it can determine horizontal and vertical components of the velocity; the system has a thorough understanding of the current structure and behavior.

5. Requirement for High-Quality Measurement of Coastal Currents near Kuakata

Materials of Equipment

The equipment used for high-quality measurement of the coastal currents near Kuakata needs to be made of reliable materials. A marine environment with saltwater, possible exposure to storms-especially during the monsoon season-and the influence of tides and ocean currents requires a casing that is durable. The size of the equipment should be small for easy deployment and retrieval, considering that the sea is sometimes rough and that there is a beach and other coastal structures.

Design Considerations

A light weight design is desirable since it makes the equipment more manageable during installation and maintenance. Low power consumption is important for long - term and autonomous operation. Cost - effectiveness is also an issue to enable large - scale measurements, considering the local economic and resource constraints.

Casing Material for ADCPs

The casing of ADCPs is preferably made of materials with excellent corrosion resistance such as titanium alloy or high - grade stainless steel. These materials can withstand the corrosive effects of seawater. They are also strong and durable, capable of withstanding the pressure of the water at different depths. Their lightweight nature (especially titanium alloy) makes them more convenient for various deployment methods.

6. Selection of Appropriate Equipment for Current Measurement at Kuakata

Purpose-Based Selection

While selecting the equipment to measure the current at Kuakata, first, one needs to think about the purpose. If the measurement is for a vessel's navigation or short-term research related to surface conditions, such as for local fishing boats, either a ship-mounted ADCP or a simple surface-drifting buoy system can be considered. The ship-mounted ADCP meter provides real-time current information during the voyage, while the buoy can give a general idea of the surface current.

Seabed-related Measurements For measurements near the seabed, such as in studying sediment transport, which is important owing to the sandy beach and possible coastal erosion, or benthic ecology, a bottom-mounted ADCP flow meter is preferred since it will be able to capture the details of the near-bottom current, which is very important to understand the sediment movement and its impact on the seabed and the beach.

Long-Term and Wide-Area Monitoring If the monitoring of the coastal current needs to be done for a long period and over a wide area, the buoy-type ADCP current profiler would be ideal. It can continuously provide data for an extended period and cover a relatively large area, which can help to understand the overall patterns and changes in the coastal currents.

Frequency Consideration for ADCPs

Frequency-wise, a 600kHz ADCP is a good choice for water depths up to 70m, which would cover much of the coastal area near Kuakata. For deeper waters, such as those that may be encountered in some offshore areas or in channels, an ADCP current meter frequency of 300kHz or lower (depending on the depth) would be more appropriate. 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 trade-off between accuracy and range.

There are well-known brands of ADCPs such as Teledyne RDI, Nortek, and Sontek. However, for those looking for a cost-effective option with good quality, the China Sonar PandaADCP is highly recommended. It is made of all-titanium alloy material and offers an incredible price-performance ratio. You can find out more about it on its website: https://china-sonar.com/.

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