ADCP's Application in Flood Management of Indus River

1. Where does Indus River flow?

Indus River is one of the major rivers of Asia that originates in the Tibetan Plateau near Lake Manasarovar in China and flows through India down to Pakistan. The length of this river is about 3,180 kilometers.

The Indus River has a basin that contains all kinds of terrain: from high mountains to arid plains and highly fertile agricultural regions. It runs through major cities like Karachi in Pakistan and forms the lifeline of millions of people. The climate varies accordingly, with the upper reaches being cold and dry while the lower reaches have a more arid and hot climate. For irrigation, it requires water, which then supports the vast amount of agriculture in the region.

The rainfall in the Indus River basin is highly varied. The upper reaches receive precipitation in the form of snow and rain; snowmelt provides a substantial amount of the river's flow. In the lower plains, the rainfall is sparse and irregular. Besides, there may be a major contribution due to monsoon rains, with a large inflow during the wet season between July and September.

2. What are the reasons for floods in Indus River?

Monsoon Rains: The main factor causing floods in the Indus River is intense rainfall during the monsoon. The river's basin has a large catchment area due to which it carries enormous water collected during the monsoon season. The tributaries funneled the water to the main river channel. If the volume of water exceeds the natural carrying capacity of the river, it causes flooding.

Snowmelt: Snowmelt from the upper reaches can also contribute to a flooding stage. When the snow that fell during winter and accumulated rapidly melts either in spring or along with heavy rains, the water amount becomes substantial in the river.

Deforestation and Change in Land Use: This is due to human activities like deforestation and urban expansion that have taken place within the river basin, ultimately decreasing its ability to absorb water. Deforestation has generally resulted in a surge of surface runoff, thus adding more water to the river and increasing flood risk.

Within the context of flood management, Acoustic Doppler Current Profiler (ADCP) has become a more sophisticated and effective measuring device than conventional methods.

3. How do ADCPs using the principle of Doppler work?

The principle behind the working of ADCPs is the Doppler principle. They emit acoustic signals into the water, which interact with moving particles in the water, such as sediment particles and water molecules flowing with the current. When the emitted waves are reflected back by these moving objects, a change in frequency occurs.

This frequency change, or Doppler shift, is proportional to the velocity of the moving objects. ADCPs have multiple transducers that transmit acoustic pulses in several directions. A downward-looking ADCP current meter, for instance, can measure the velocity profile of the water column from the water surface to the riverbed. With the ADCP current profiler, analyzing the Doppler shifts of the reflected signals from different depths within the water column allows it to calculate the velocity of the water flow at each depth.

From this velocity information and by considering the known cross-sectional area of the river at the measurement location, it is then possible to calculate other important parameters like the flow rate of the river.

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

Velocity Measurement: This has a broad range of applications during the flooding of the Indus River, whereby ADCP flow meter can be correctly deployed to measure the velocity of water flow at different locations and depths. This information is indispensable in ascertaining the velocity at which floodwaters are moving. For instance, it can be used to identify the exact time when floodwater reaches agricultural fields, villages, or cities that are very vulnerable. Continuously observing the velocity will allow authorities to take measures necessary for the people and to strengthen embankments.

Flow Measurement Application: The ADCP meter computes the flow rate of the river by integrating the velocity data over the cross-sectional area of the river. During any flood event, this would be able to give the total volume of water passing through a particular section of a river. This is important in flood forecasting in terms of the magnitude of the flood. It can help in evaluating the various flood-control structures, such as levees and dams.

Sediment Transport Research Application: The ADCP profiler can analyze the backscattered acoustic signals as the floodwaters of the Indus River carry sediments. Understanding sediment transport during floods is important because of assessing changes in the riverbed. Sediment deposition and erosion alter the depth, width, and stability of the river, which affects future flood risks and the health of the river ecosystem.

5. How does the data measured by ADCP help in flood warning and risk management of Indus River?

Flood Warning

Velocity and Flow Data Monitoring: This allows for continuous monitoring of the velocity and flow data through ADCP current meter, thereby giving an early warning in case of abnormal changes in the flow of the river. A sudden increase in velocity or a significant change in flow rate can indicate the approach or intensification of a flood. The provided data can thus be integrated into flood warning systems that issue timely warnings to the public and concerned authorities.

Water Level Prediction and Warning: Measured flow data from ADCPs can be combined with other factors, including the cross-sectional geometry of the river and historical records of water level, to predict future water levels. A warning in advance can be issued if the water level is predicted to exceed the flood level mark to enable people to move or protective measures.

Risk Management

Water Conservancy Project Scheduling Decision Support: The ADCP data is highly useful in the decision-making process over operations of water-conservancy projects like dams, reservoirs, and diversion channels along the Indus River. For instance, in the case of a flood, the flow data can help to determine an optimal release rate from the dam to mitigate the impact of the flood downstream.

Assessment of Flood Disaster and Emergency Response: In events where a flood has occurred, the data from the ADCP current profiler can be used to assess the level of damage caused by the flood. This includes assessing the areas affected by high - velocity flows, the amount of sediment deposition, amongst others. This information is useful for guiding emergency response and recovery efforts, such as search and rescue operations and post-flood rehabilitation of infrastructure and ecosystems.

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

Much is needed for high-quality measurement of the Indus River currents.

Reliable equipment materials: The ADCP flow meter has to be manufactured from materials that can withstand the harsh conditions in the Indus River environment. It should be resistant to corrosion from the river water, impacts from floating debris, and abrasion from sediment particles.

Small Size, Light Weight, and Low Power Consumption: The more compact and lightweight ADCP meter, the easier it is to install and deploy, which may have otherwise been difficult to access. Low power consumption allows operation over longer periods without frequent changes in batteries or complex power arrangements, enabling continuous and long-term monitoring.

Low Cost: The device should be lower-cost to allow for large-scale deployment in order to effectively monitor the entire length of the river.

About the casing material, titanium alloy would be an excellent choice. Titanium alloy has high strength to help ADCP profiler resist outer forces. It also has excellent corrosion resistance to support the equipment in continuously ensuring performance in the water. Its relatively low density helps reduce the overall weight of the device without losing any aspect of its structural integrity.

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

When choosing equipment for current measurement in the Indus River, consider the following:

Purpose of Use: If the focus is on horizontal cross-sectional flow measurement, a Horizontal Acoustic Doppler Current Profiler is suitable for choice. It measures the flow velocity and other parameters across a horizontal section of the river. In cases where the measurement deals with a vertical cross-section, a vertical ADCP current meter will be more appropriate since it can measure the velocity profile from the water surface to the riverbed along a vertical line.

Frequency Selection: ADCPs of different frequencies are suitable for different water-depth ranges. For instance, a 600 kHz frequency ADCP is generally suitable for water depths up to 70 meters, whereas the ADCP with 300 kHz is more appropriate for water depths up to 110 meters. The correct frequency should be chosen based on the actual water depth of the Indus River to ensure that accurate and reliable measurement results are obtained.

There are well-known ADCP profiler brands such as Teledyne RDI, Nortek, and Sontek. Additionally, there is a Chinese brand, China Sonar PandaADCP, which features a casing made of titanium alloy and offers a good cost - performance ratio. You can visit its website (https://china-sonar.com/) for more information.

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