How to measure the Coastal Currents of Preah Sihanouk?

1. Location of Preah Sihanouk

Preah Sihanouk is a Cambodian province located on its south-western coast along the Gulf of Thailand. This area hosts some fantastic beaches such as Otres Beach and Serendipity Beach, which are rather famous among tourists.

Preah Sihanouk-Sihanoukville is a large port city and economic hub currently on the rise. It has a very mixed population, consisting of Cambodians and many expatriates, migrants, and workers due to the burgeoning tourism and construction sectors there.

The nearby Gulf of Thailand is shallow and warm, considering its general depth. Its waters along the coasts are full of marine life, filled with various fish species, crustaceans, and mollusks. And there are large areas of coral reefs in that area which add to the biodiversity and attract snorkelers and divers.

2. What is the situation of the coastal currents near Preah Sihanouk?

In Preah Sihanouk, the coastal currents are influenced by various major factors. Tidal current is one of the huge forces. The gravitational pull of the moon and the sun has a great impact on tides in the Gulf of Thailand. The tide can be classified as semi - diurnal, where there are two high tides and two low tides around the area every day. Tidal currents, particularly near the coast and narrow passages, may be very strong. These are closely related to the transport of sediments and nutrients.

Then, the major impact of monsoon winds is very well pronounced. The southwest monsoon, between May and October brings very strong winds which at times may drive the surface currents in a specific direction. That of the northeast monsoon, between November and February alters the direction of wind and hence it may change the direction and speed of the coastal currents.

This flow of the coastal currents may be diverted and changed with regard to local bathymetry, the shape of the seabed, and possibly the presence of underwater features like ridges and channels. The discharge of local rivers and streams is generally very small compared with some other areas, though the variation in current patterns and freshwater input caused by sources can induce density differences resulting in complex current systems.

3. How to observe the Preah Sihanouk coastal water flow?

There are various ways in observing the Preah Sihanouk coastal water flow.

Surface Drifting Buoy Method

It is a somewhat simple and even practical technique. Buoys are deployed in the water, equipped with GPS or other types of tracking instruments. As these buoys drift with the currents, it can be tracked over a period to determine the speed and direction of the surface currents. Such buoys would need to be resilient enough to withstand all local marine conditions, including those linked with waves and saltwater.

Anchored Ship Method A ship is taken to the location and anchored, from which current-measuring instruments are suspended. These are the instruments that measure the velocity and direction of water flow at each depth. This method has certain shortcomings. The ship may be influenced by wind and waves; this could lead to lesser accuracy in measurement. It is also somewhat uneconomical for operations covering large areas.

The Acoustic Doppler Current Profiler Method

This is more advanced and efficient in measuring coastal water flow. In general, an ADCP current meter is able to measure the velocity profile of the water current over a wide range of depths. The basic principle these work on is emitting sound waves in the water and, based on the returned waves, analyzing the Doppler shift in them. Based on that, it gives quite a clear idea about the current structure from the surface to the seabed.

4. How Do ADCPs Using the Doppler Principle Work?

The ADCPs apply the Doppler Principle. An Acoustic Doppler Current Profiler (ADCP) sends out acoustic pulses-chapter commonly referred to as 'sound waves'-through water. These sound waves emitted in the water scatter off particles in the water such as sediment, plankton, and other small particles. Whenever these emitted sound waves reflect from these particles back to the ADCP, the frequency of the reflected waves has changed because of the Doppler effect.

In this case, if the particles move towards the ADCP doppler, the frequency of the reflected wave is higher than that originally emitted. If they are moving away from the ADCP, the frequency of the reflected wave will be lower. By precisely measuring this shift in frequency, the ADCP becomes able to figure out the velocity of the particles. Since the particles are moving with the water current, the velocity of the particles estimated through the calculation is the measure of the water current's velocity.

They can transmit the sound pulses in many directions, allowing them to measure the current velocity in three - dimensional space and at depth intervals. For example, a vertical profile would normally be utilized in measuring the current velocity from the surface to the seabed and vice versa at regular intervals for a detailed signature of the current structure.

5. What is needed for quality measurement of the coastal currents in Preah Sihanouk?

For the high-quality measurement in the coastal currents of Preah Sihanouk, the equipment should be made of reliable materials. Casings have to be really durable since the conditions of the marine environment are very harsh due to saltwater corrosion and possible physical impacts because of waves and debris.

The size of the equipment has to be sufficiently small so that it may easily be deployed, especially at places where there is less access to deploy, as in small boats or shallow coastal waters. A lightweight design is also conducive for easy handling and installation.

Low power consumption for long - term measurements is important. Cost - effectiveness is similarly important so that large-scale measurements are feasible. In the case of ADCPs, the casing is preferably made from titanium alloy. Titanium alloy has excellent corrosion resistance, which is essential in Preah Sihanouk's marine environment, whereby this resistance can fight against the corrosive action of saltwater over a long period. It is also strong and has a high strength-to-weight ratio, thus providing a durable but lightweight structure that can house the internal components of the ADCP flow meter.

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

Concerning the selection of appropriate equipment for measurements of currents at Preah Sihanouk, the first one is the issue of using such equipment.

For Measurements from a Moving Vessel

A ship-borne ADCP flow meter would be sufficient for the exercise. It can provide current data in real time as the ship is in motion and can, therefore, afford a reasonable interpretation of the water flow at different locations.

For Measurements at a Fixed Location near the Seabed

For example, a bottom-mounted ADCP doppler would be useful. A current could be continuously monitored at a point effectively and consistently capture data over a period of time.

For Measurements to be Made over a Large Area without Restraint to a Specific Depth Buoy-type ADCP current profiler would fit. It makes the measurement over a larger area. The restriction for the measurement is not limited to a particular depth.

For the choice of frequency, up to 70m water depth, a frequency of 600kHz for ADCP would suffice; from 70 - 110m, a frequency of 300kHz will be better. In waters as deep as 1000m, the recommended frequency is 75kHz.

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 a great cost - performance ratio. You can find more information about it on the website: https://china-sonar.com/.

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