ADCP in the Mun River Flood Management

1. Where is the Mun River?

The Mun River is one of the major rivers in Thailand originating from the Phetchabun Mountains to the north of Thailand.

It actually courses its way through various provinces and cities in the country geographically. Some of the major cities it passes through include Nakhon Ratchasima. It curves through the middle and northeastern parts of the country; this makes it very important in the aquestic system and farming for the people in that region.

From a rainfall perspective, Thailand, where the Mun River is located, has a marked wet and dry season. In the wet season, there is usually copious rainfall from May to October. Most days are frequently overcast with heavy downpours. Because of this, in the Mun River, there is a big rise in water. Rainfall varies from year to year; however, the general picture is that most of the monsoon rains account for a high percentage of the water in the river during the wet season.

2. Why do floods occur in the Mun River?

There are a few reasons for the occurrence of flooding in the Mun River. The first one would be heavy rainfall during the wet season. As mentioned above, when heavy monsoon rains hit the area, if the river's drainage capacity cannot bear such a sudden amount of water, the water level is sure to surge and flood.

Second, topographic features along the basin contribute to changes in the flow of water. Parts of the stream bed with flat terrain allow the slowing down of the water current and therefore water accumulation is easily possible. Human activities, on the other hand, contribute to such occurrences, for example, deforestation at the upper reaches of a river. These activities reduce soil cohesion and enhance soil erosion. This, in turn, becomes responsible for deposition in the river channel and reduces carrying capacity, hence more floods are caused.

Recently, with urbanization and development of agriculture, impervious surfaces have been increasing with a change in land use pattern. These changes have modified the natural hydrologic cycle and thus deteriorated the flood situation in the Mun River area.

ADCP current profiler is an acoustic Doppler current profiler that has come up to be a more advanced and convenient measurement technique in further understanding and managing the flow conditions of the river during flood events.

3. How do ADCPs using the Doppler principle work?

Basic Principle: Acoustic Doppler Current Profiler(ADCP) work according to the Doppler principle. When an acoustic signal is emitted by the ADCP into the water, it comes into contact with moving particles of water. Because of the flowing water, the frequency of the reflected acoustic signal is changed by the Doppler effect.

The ADCP measures the differential frequency emitted and received of the acoustic signal. By analyzing this frequency shift, it can calculate the water velocity at discrete depths. The instrument is usually mounted with a set of transducers capable of transmitting and receiving acoustic signals in different directions, hence providing a profile of the water velocity over a cross-section of the river.

For example, if the water is going towards the ADCP doppler, the reflected signal would have a higher frequency than the emitted one; if it is going away, the opposite happens. Exactly through these changes in frequency, with the use of an appropriate algorithm, the ADCP current meter is able to obtain the real value of the velocity of water at different points of its measurement range.

4. What are the applications of ADCP in the Mun River floods?

4.1 Velocity Measurement

During the flooding occasions in Mun River, ADCP flow meter can be of help to measure the flow velocity with more precision. With the continuous current measurements of water velocity at different depths and locations, it gives real-time data about the velocity of the water movement. This will come in handy when needed to understand the dynamics of a flood .

4.2 Flow Measurement Application

ADCP meter can also be used to measure flow rate in the Mun River. It sums up the measured water velocities at different points across a section of the river using the known cross-sectional area of the river to calculate the total amount of water actually passing through that section in every unit time, which is the flow rate. This information becomes indispensable in estimating the total volume of water during a flood and in decision-making processes for flood control and management of water resources.

4.3 Application in Sediment Transport Research

Apart from flow and velocity, ADCP profiler also finds its application in sediment transport studies in the Mun River during a flood. While water is flowing, it can carry sediments, and an doppler current profiler would be able to detect changes in the backscattered acoustic signal due to the presence of sediments. These changes can be analyzed in order for estimations of quantity and movements of sediments to be obtained-a fact quite important for the understanding of the long-term evolution of the riverbed and for assessing the impact of floods on the sedimentary environment of this river.

5. How does the data measured by ADCP contribute to enabling flood warning and risk management of the Mun River?

5.1 Flood Warning

Monitoring of Flow and Velocity Data: In respect to this, the acoustic doppler flow meter continuously monitors the actual velocity and flow data in real time. If the measured water velocity exceeds the threshold value or the flow rate increases sharply, it would signify the approach of a flood peak or a possible flood situation. With this timely warning, relevant authorities will be able to take effective measures, including evacuation of people in low-lying areas or strengthening of flood defenses. Water Level Prediction and Warning: Measured flow data is correlated with historical water level data to predict the future water level using ADCP data with the help of appropriate hydrological models. If the predicted water level is forecasted to rise above the flood warning level, timely warnings can be issued to the public to get ready for the flood.

5.2 Risk Management

Water Conservancy Project Scheduling Decision Support: Accurate flow and velocity data from ADCP will support decisions regarding operating, such as water conservancy projects, including dams and sluices. It may decide how much to release water from a dam according to the measured flow of the water that could control the water level in the Mun River during flooding. Flood Disaster Assessment and Emergency Response: In the event of a flood, data collected by acoustic doppler velocity meter will give an estimate of the inundation magnitude, velocity of flood flow, and deposition of sediment. This information is very helpful in identifying the course of emergency response and subsequent post-flood construction and rehabilitation works.

6. What is required for high-quality measurement of the Mun River currents?

Some of the important factors for high quality measurement of Mun River currents are as follows: the equipment used in the measurement process should be of reliable materials. The casing of the ADCP is of great importance. It is recommended that the casing should be made of a titanium alloy. Titanium alloy has several advantages. This material has high strength, which allows the device to withstand pressures and impacts caused by the water that circulates in the river. It is also a very resistant material against corrosion, critical under the conditions of the Mun River's environment, where there could possibly be various corrosive materials in the water.

As for the size and weight, it shall be as small and light as possible, besides considering the reliability of the material. This makes it easier to install and operate the ADCP in different locations along the river, especially in areas that are difficult to access. Low power consumption is also important because it can work continuously for a very long period of time without changing the batteries frequently or hooking up the device to a power source. The equipment cost should be relatively low to enable measurements on a large scale. A lower cost simply means that more ADCPs can be deployed down the Mun River, which will provide more adequate detailed data in relation to flood management.

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

In choosing the right equipment for current measurement in the Mun River, several factors have to be considered: first, related to the type of measurement required, if it is for horizontal cross-section measurement, then a Horizontal ADCP should be chosen while a Vertical ADCP will serve if it were for vertical cross-section measurement.

Secondly, at different water depths, different frequencies are appropriate. As an example, the ADCP at 600 kHz will serve for water depths within 70 m. Therefore, when the water depth in the Mun River is within this range, a frequency of 600 kHz can be considered if the measurement requirements correspond to that. For depths over 70 m, reaching up to 110 m, the ADCP at 300 kHz will be more appropriate and serve at an improved result.

Well-recognized brands in the market include Teledyne RDI, Nortek, and Sontek. However, China Sonar PandaADCP is quite an economical alternative for users. It is fabricated from all-titanum alloy material, so one can be certain of its resistance to failure and ever being reliable in water. Moreover, its price has an incredible cost-performance ratio. You can learn more about it on its website: https://china-sonar.com/

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