ADCP's Application in Flood Management of the Irrawaddy

1. Where is the Irrawaddy?

The Irrawaddy River is the largest and most important river in Myanmar. It flows through the heart of the country, stretching over 2,170 kilometers (1,350 miles). The river's source is in the Kachin State, near the border with China.

It passes through major cities such as Mandalay and Yangon. The climate in the Irrawaddy basin is tropical monsoon. There are distinct wet and dry seasons. The wet season, which usually lasts from May to October, brings heavy rainfall. The amount of rainfall during this period is significant and is the main source of water for the river. In contrast, the dry season, from November to April, sees much less precipitation. In addition, the snowmelt from the upper reaches in the northern mountains contributes to the volume of water in the river during appropriate seasons.

2. What are the causes of floods along the Irrawaddy?

A number of factors predispose the Irrawaddy to flooding. Most outstanding is the monsoon rainfall. During the rainy season, the heavy and sustained rainfall can bring an almost sudden rise in the river. The tributaries also contribute a very large volume of water to the main river channel, beyond its capacity.

Other factors include topography and river morphology. The plains through which the river courses have very poor natural drainage. Thus, whenever the level of water rises in the catchment areas, water easily spills over into the floodplains. Moreover, the natural ability of the soil to absorb water and check runoff has been further weakened by deforestation and other changes in land use within the catchment area of the river.

Another problem is sedimentation. The gradual process of depositing sediment can raise the level of the riverbed over time, hence reducing the depth and capacity of flow in a river. When this coincides with heavy rainfall and other variables, frequent and severe flooding can occur.

In this light, Acoustic Doppler Current Profiler (ADCP) offers a far more modern and efficient means of measurement compared to the conventionally applied methodologies, which is essential in managing flood occurrences.

3. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of the Doppler effect. They send acoustic pulses into the water. These pulses interact with moving particles in the water, such as sediment, plankton, and other small organisms. When the acoustic waves bounce back after hitting these moving objects, a frequency shift occurs.

The magnitude of this frequency shift is directly related to the velocity of the moving particles and, thus, the velocity of the water. For instance, if an ADCP meter is placed on a boat in the Irrawaddy River, it sends out sound waves that penetrate the water column. With the waves reflected back by the flowing water and its constituents, ADCP analyzes the received signals to compute the speed and direction of water flow at different depths.

4. What are the applications of ADCP in floods of the Irrawaddy?

Flow velocity measurement: ADCP can measure the velocity of water flow in the Irrawaddy with good accuracy. This is highly valuable during flood events when understanding the speed at which floodwaters are moving is critical. It helps in predicting the spread of the flood and identifying areas where high-velocity flows may cause erosion or other damage.

low Rate Measurement: Measured velocities, combined with the cross-sectional area of the river (also derivable from ADCP flow meter), produce the flow rate of the river. In the context of a flood, knowing the flow rate is essential in assessing the volume of water passing through a particular section of the river and predicting its impact downstream.

Sediment transport studies: In general, ADCP can trace sediment particles moving along with the flow of water. In the case of flood events, this will very well portray how much sediment the river is carrying. Sediment transport studies are essential in anticipating changes within the riverbed as it gives an idea concerning the stability of the river and supporting structures.

5. How can the ADCP data be employed for flood warning and the risk management of Irrawaddy?

Flood Warning

Flow Velocity and Flow Rate Data Monitoring: With continuous monitoring of flow velocities and flow rates by an ADCP current profiler, it is possible to catch any abnormal changes in advance that may indicate an imminent flood. If the velocity or rate of flow goes above the normal level, an alarm can be triggered so that communities along the riverbanks may be given timely warnings.

Water Level Prediction and Warning: Based on the established relation between the flow rate, velocities, and water levels derived from history and measurements by means of an ADCP current meter, forecasts of the water level can be done. This information proves to be of great importance regarding warnings provided to residents; thus enabling them to take precautionary measures regarding evacuation and flood proofing in advance.

Risk Management

Water conservancy project scheduling decision-support: The data obtained by means of ADCP is valuable during the decision-making process that precedes the operation of various structures, such as dams or other water conservancy projects on the Irrawaddy River. A classic example is that, based on this advance information, in the event of a predicted flood, one can adjust the release from upstream reservoirs by using ADCP-measured data to reduce downstream flooding while maintaining the safety of these facilities.

Flood disaster assessment and emergency response: After a flood event, ADCP data can be used to assess the extent of damage, including erosion, changes in the riverbed, and the impact on infrastructure. This information guides emergency response efforts and future flood mitigation strategies.

6. What's needed for high - quality measurement of the Irrawaddy currents?

It should have reliable materials for high-quality measurement of the Irrawaddy currents. A compact size and light weight would, therefore, be an added advantage in its application because this would allow its easy deployment at many locations along the river, even on boats or bridges. Low power consumption would allow it to be useful for long-term monitoring, where power supply can hardly be afforded. Besides, it is cost-effective to allow wide deployments for comprehensive monitoring.

The casing of ADCP is preferably made of titanium alloy. Titanium alloy offers excellent corrosion resistance, which is needed with the Irrawaddy's water that may contain various minerals and salts. It also has a good strength-to-weight ratio, making the equipment durable and relatively easy to handle and install.

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

If selecting the equipment for the measurement of the current in the Irrawaddy, it will be taken into account. It should apply horizontal - ADCP (HADCP), measuring flow velocities through a horizontal plane in order to achieve clarity over the general flow pattern for some selected reaches in a river. To collect data in a vertical cross-section, the Vertical ADCP will profile, within a vertical line, water velocities from the surface down to the riverbed.

Accordingly, an ADCP at the frequency of 600 kHz works appropriate at up to 70 m of water depths while a frequency of 300 kHz allows coverage in sections up to approximately 110 meters of water.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option, the China Sonar PandaADCP is recommended. It is made of all - titanium alloy materials and offers a good cost - performance ratio. You can find more information at (https://china-sonar.com/).

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