How to Measure the Water Current of the Mun River

1. Where is the Mun River?

The Mun River is a major river in Thailand. It is one of the biggest affluents of the Mekong River. It has its source in the Phetchabun Mountains and flows through northeastern Thailand.

This river cuts through agricultural landscapes where it ensures irrigation for crops such as rice, sugarcane, and cassava. The Mun River also provides a means of transportation for the people in this area. Locals move around with their goods using boats and barges. Various fish species, including catfish and carp, are found in the river's ecosystem. The riverbanks support populations of waterbirds, snakes, and other wildlife. Floodplains and wetlands along the river are crucial in maintaining ecological cycles, acting as important breeding and feeding areas for a variety of species.

2. What is the nature of flow in the Mun River?

The flow rate of the Mun River is seasonal and varies climatically. Normally, during the monsoon season-from May to October-heavy rainfall falls in the catchment area of the river. This raises its flow rate tremendously. The river swells and can carry a large volume of water during this period.

It starts to recede during the dry season, which begins in November and generally lasts until April. During this time, the base flow is maintained, which is critical for the survival of the aquatic life and to sustain the livelihood activities of the local communities related to fishing and transportation. The average flow can vary from a few hundred cubic meters per second during the dry season up to several thousand cubic meters per second during the peak of the monsoon season.

3. How to measure water current of the Mun River?

Velocity Meter Method

This traditional method uses mechanical or electronic velocity meters. These instruments are located at discrete points in the river and directly measure the current velocity of the water at that location. However, to gain an overall appreciation of the water current, several measurements are taken at a variety of depths and over various reaches of the river. Due to the length and changing nature of the Mun River, this can be time-consuming and labor-intensive.

Acoustic Doppler Current Profiler (ADCP) Method 

ADCP represents a more sophisticated and handy method of water current measurement. It relies on the interaction of sound waves with water particles. While emitting acoustic signals and analyzing the Doppler shift of reflected signals, it allows for simultaneous measurement of water velocity at several depths. This gives a very accurate profile of the water current, which enables a more appropriate estimation of the flow conditions along the whole river. ADCPs can be installed on boats if the conditions are navigable, on bridges if available, and also on buoys for continuous monitoring.

Buoy Method

In the buoy method, buoys are put into the river, carrying sensors that measure the movement of water around them. These buoys float on the surface and provide at least some indication of the surface current. They might not catch the full detail of the water current quite as well as the other methods, particularly in relation to how the velocity can change with depth.

Of these, the ADCP is more advanced and efficient to measure the water current of the Mun River.

4. How do the ADCPs apply the principle of Doppler?

ADCPs are designed based on the Doppler principle. In operation, an ADCP sends an acoustic signal into the water. The sound waves travel through the water and interact with the moving water particles. Due to the moving nature of the water particles, the frequency of the reflected sound waves changes by the Doppler effect.

If the water particles are moving towards the ADCP, then the frequency of the reflected wave will be higher than the frequency it had when it was emitted. If the water particles are moving away from the ADCP, then the frequency of the reflected wave will be lower. By precisely measuring this change in frequency, the ADCP calculates the velocity of the water particles at various depths.

The ADCP combines these individual velocity measurements at different depths into one complete profile of the water current. This enables detailed insight into how the water flows not only at the surface but throughout the vertical section of the river.

5. What's required for high-quality measurement of the Mun river currents?

Measurement of the Mun River currents, in this case, requires equipment with specific characteristics for high-quality measurement.

The equipment used for this purpose has to be highly reliable in terms of material. It should be able to resist adverse conditions such as those from exposure to water and sediment particles and temperature fluctuations that occur in the river. Variable flow in the Mun River and debris, such as logs and tree branches that occur during periods of high flows, requires durable equipment.

It is also desirable to be in a small size, lightweight, and with low power consumption. The compact and lightweight device is easy to handle and deploy both on a boat and attached to a buoy. Low power consumption means the equipment will be able to operate for a very long time without requiring frequent battery replacements or access to a continuous power source.

The cost-effectiveness of the choice is an important factor. A lower cost would allow more widespread use of the measurement equipment and permit a broader monitoring scope over the river.

For the ADCP casing, the best material is titanium alloy. The resistance of titanium alloy to corrosion is particularly high, making it an ideal choice when dealing with water bodies like the Mun River, where equipment constantly stays in contact with water and other substances that could cause corrosion. It is also strong and resilient to physical impacts and any changes in pressure during deployment and operation. Besides, titanium alloy has a relatively low density that contributes to keeping the equipment light as a whole.

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

Some things must be considered while choosing appropriate equipment to measure the current of the Mun River.

Based on the Purpose of Use

If, for example, the horizontal cross-section of the river current is to be measured, then an HADCP is used. Basically, HADCPs provide very accurate measurements concerning the flow of water in the horizontal plane, which is useful for understanding the overall movement of water across a particular section of the river.

If the focus is to measure the vertical cross - section of the river current, a vertical ADCP should be selected. Vertical ADCPs can measure with precision the velocity of the water at different depths, creating a detailed profile of how the water flows vertically within the river.

Based on Frequency

Frequency selection depends on the depth of water in the Mun River. For a depth up to 70 meters, 600 kHz ADCP is normally suitable. The frequency of 600 kHz gives good resolution and accuracy for measuring the current of water in relatively shallower waters.

A 300 kHz ADCP is more fitted in application to deeper waters, such as those over 70 meters up to about 110 meters. The low-frequency rate of 300 kHz can reach deeper into the water and still give good results for measuring the current of the water.

There are renowned ADCP brands, including Teledyne RDI, Nortek, and Sontek. However, for those seeking a cost - effective option with excellent quality, the China Sonar PandaADCP is worth considering. It is made of all - titanium alloy material, ensuring durability and reliability. With its remarkable cost - performance ratio, it provides a great alternative for measuring the water current of the Mun River. You can find more information about it on its official website: https://china-sonar.com/.

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