ADCP's Application in Flood Management of the Padma River

1. Where is the Padma River?

The Padma River is a major river in South Asia. It is the main distributary of the Ganges River as it enters Bangladesh. The river forms a significant part of the border between India and Bangladesh.

It passes through many densely populated regions and important cities such as Rajshahi in Bangladesh. The climate in the Padma River basin is tropical monsoon. There are marked wet and dry seasons. The wet season, generally from June to September, is highly rainy. This rainfall, along with the water coming from upstream tributaries, swells the river. During the dry season, the water level is relatively lower, but the river still maintains a certain flow because of the groundwater seepage and other factors.

2. What are the causes of flooding in the Padma River?

Flooding in the Padma River is largely caused by monsoon rains. The heavy and consecutive rains during the wet season bring about a sudden rise in the water level of the river. The enormous catchment area of the river and its innumerable tributaries carry a huge volume of water, which can easily exceed the river's carrying capacity.

The second reason is the flat topography of the region through which it flows. The floodplains have limited natural drainage, and when the water level rises, it spreads over a wide area, inundating vast tracts of land. Another problem is sedimentation. Over time, the deposition of sediment can raise the riverbed, reducing the depth and flow capacity of the river, making it more prone to flooding.

On the other hand, human -caused changes, like the top catchment area being removed due to deforestation or construction of embankments not being adequately designed, contribute to flood hazards. Against this backdrop, in this regard, ADCPs have proven to be superior to more conventional methods related to managing a flooding problem.

3. How do the ADCPs based on the principle of the Doppler principle operate?

The basic operation of ADCPs is based on the Doppler principle. ADCPs emit an acoustic pulse into the water. These pulses interact with moving particles in the water, such as sediment, plankton, and other small organisms. When these acoustic waves bounce back upon hitting such moving entities, a frequency shift takes place.

This frequency shift depends directly on the velocity of those moving objects and, by extension, the velocity of the water. For instance, an ADCP current meter placed in the Padma River-say, on a boat or a fixed structure near the riverbank-emits sound waves that penetrate the water column. While the waves are reflected back by the flowing water and its constituents, the ADCP analyzes the received signals to calculate the speed and direction of the water flow at different depths.

4. What are the uses of an ADCP in floods in the Padma River?

Flow velocity measurement: The ADCP current profiler may very well estimate the correct value of flow velocity on the Padma River. This information, during flooding, will give a real-time view of how much flood flow velocity is observed. Therefore, in effect, it aids in spreading the flood and pinpointing any zones experiencing high-velocity flows due to erosion or other loss.

Flow rate measurement: Together with the measured velocities and cross-sectional area of the river-which also can be determined using ADCP-the flow rate of the river can be calculated. During a flood, knowing the flow rate is important for assessing the volume of water passing through a particular section of the river and, hence, predicting its impact downstream.

Sediment transport studies: ADCP flow meter is able to detect the movement of sediment particles along with the water flow. In the case of floods, this will give important information about the quantity of sediment taken by the river. Knowledge of sediment transport allows, among others, the forecasting of bed variations in terms of erosion or deposition of sediment that could affect stability of the river and installations.

5. How can the data measured by ADCP be utilized in the flood warning and risk management of the Padma River?

Flood warning

Flow velocity and flow rate data monitoring: The continuous flow velocities and flow rates recorded by ADCP meter can allow for the timely detection of abnormal changes that may point to an imminent flood. If the velocities or flow rates increase beyond normal levels, an alert can be triggered to allow timely warnings to communities along the riverbanks.

Water level prediction and warning: By examining the relation between flow rates, velocities, and water levels from historical data with ADCP profiler measurements, a prediction of future water levels can be determined. The information is very important to give accurate warnings to the residents for taking necessary precautions such as evacuation or flood-proofing.

Risk management

Water Conservancy Project Scheduling Decision-support: The ADCP data is useful in making decisions related to the operation of dams, reservoirs, and other water conservancy projects along the Padma River. For instance, if a flood is forecasted, water release from the reservoirs can be regulated with the help of ADCP-measured data to reduce the occurrence of flooding downstream and to keep the structures safe.

Assessment of flood disasters and emergency response: ADCP profiler data after a flood event would be used to measure the extent of the damage regarding erosion, change in the riverbed, and its impact on infrastructure. This information guides emergency response efforts and helps in formulating future flood mitigation strategies.

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

Reliability of materials should be there with the equipment for high-quality measurement of the currents of the Padma River. Compact size and lightweight will be beneficial for easy deployment in any location along the river, including on boats or bridges. Low power consumption will enable long-term monitoring, especially in areas where there is limited power supply. The cost should be as low as possible to enable deployment at large numbers for comprehensive monitoring.

The casing of ADCP meter is preferably made of titanium alloy. Titanium alloy provides excellent corrosion resistance, which is essential when dealing with Padma River water that may contain various minerals and salts. It also has a good strength-to-weight ratio that makes the equipment durable and relatively easy to handle and install.

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

In selecting the equipment for the current measurement in the Padma River, the following will be considered. A horizontal ADCP, HADCP, is suited for measurements in a horizontal cross-section. It measures flow velocities across a horizontal plane, giving a clear overview of the general flow pattern within a reach of the river. In the case of vertical cross-section measurements, the Vertical ADCP flow meter is ideal since it profiles the velocities from the water surface to the riverbed along a vertical line.

An ADCP current profiler frequency of 600 kHz is suitable for water depths up to approximately 70m. Sections deeper than this require an ADCP with a frequency of 300 kHz, which best suits water depths of up to about 110m.

There are well - known ADCP current meter 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.