ADCP's Application in Flood Management of the Alaknanda (Ganga)

1. Where is the Alaknanda?

The Alaknanda is a major tributary of the Ganges River in the Indian Himalayas. It originates from the Satopanth Glacier and the Bhagirathi Kharak Glacier. The river flows through the mountainous regions of Uttarakhand in India.

It passes through a number of small towns and pilgrimage places, including Badrinath. The climate in the Alaknanda basin is very much influenced by its high - altitude location. For a major part of the year, its upper reaches are cold and receive snowfall. As it descends, the climate changes but still has a marked influence from the Himalayan weather patterns. The snowmelt during the hotter months and rainfall during the monsoon season feed the river.

2. What are the reasons of flood in Alaknanda?

Flooding in the Alaknanda River is a result of various factors: snowmelt being the major one. With the great amount of snow in the upper Himalayas, its melting during the spring and the early summer months can instantly fill up the river with so much water. If the snow melts too fast and the river can't bear the quantity downstream, this may cause flooding.

The rainfall of the monsoon also plays a very important factor. The heavy and frequent rains that usually take place in the monsoon season from June to September raise the river's level incredibly fast. The combination of snowmelt and the heavy rainfall can be rather disastrous.

Another factor is topography: the topography of the Alaknanda River runs through narrow valleys and mountainous regions. Within such regions, landslides and debris flows are common that can block the course of the river and cause water to backup, resulting in floods.

In this context, the ADCP current meter is more advanced and efficient as a measurement tool than traditional methods, thereby allowing better flood management.

3. How do ADCPs using the principle of the Doppler 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 grains, small aquatic organisms, and other suspended matter. When the acoustic waves bounce back after hitting these moving objects, a frequency shift occurs.

The magnitude of this Doppler shift is directly proportional to the velocity of the targets in motion and, thus, the water velocity. If, for instance, an ADCP current meter is installed in Alaknanda, on either a floating platform or mounted against a fixed platform on the riverbank, the unit emits sound waves deep into the water column. The ADCP works by analyzing the signals received, reflected back by the flowing water and its constituents, to calculate the speed and direction of the water flow at different depths.

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

Velocity measurement of flow: In this regard, ADCP current profiler would be able to provide very exact measurements of the Alaknanda's flow velocity. This input is very valuable in judging the speed at which floodwater is traveling during flood periods. It helps in predicting the nature of flood progress, such as how soon it will reach downstream areas or which areas may be vulnerable to erosion due to high-velocity flows.

Discharge measurement: Measured velocities combined with the cross-sectional area of the river, also determinable using ADCP flow meter, can yield the flow rate of the river. In context to a flood, understanding the flow rate is necessary for calculating the volume of water passing through a particular section of the river and predicting the overall impact on downstream regions.

Sediment transport studies: ADCP meter is able to detect the actual movement of sediment particles with the flow of water. This is quite useful during floods because it helps in understanding how much sediment load the river is carrying. Understanding sediment transport helps in predicting changes in the riverbed, such as areas of sediment deposition or erosion, which can have implications for the stability of riverbanks and infrastructure.

5. How does the ADCP-measured data be utilized in flood warning and risk management of the Alaknanda?

Flood Warning

Flow velocity and flow rate data monitoring: With ADCP, continuous monitoring of flow velocities and flow rates can be performed to allow early detection of changes that may indicate an imminent flood. For instance, if the velocities or flow rates start to increase beyond normal levels, it triggers an alert system. In this way, the authorities can issue timely warnings to the communities along the riverbanks.

Water level prediction and warning: By analyzing the relationship between flow rates, velocities, and water levels (established through historical data and ADCP measurements), future water levels can be predicted. This helps in providing accurate warnings to residents, enabling them to take appropriate preventive measures such as evacuation or flood - proofing.

Risk management

Water Conservancy Project Scheduling Decision-support: The ADCP profiler data is useful in making decisions on the operation of dams, reservoirs, and other water conservancy projects along Alaknanda. For instance, if a flood is foreseen, the release from the reservoirs can be regulated based on ADCP-measured data to avoid flooding downstream while keeping the structures safe.

Flood disaster assessment and emergency response: In the event of a flood, ADCP meter data will be used in assessing the extent of damage, such as the degree of erosion, changes in the riverbed, and the 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 Alaknanda currents?

The equipment should be made with reliable materials to provide high-quality measurement of the Alaknanda currents. The small size and light weight will be beneficial for their easy deployment at any instance in the river, either on boats or even at bridges. The consumption of low power is necessary for long-term monitoring, which may be difficult in cases of scarce power supply. Cost-effectiveness will enable wide deployment for comprehensive monitoring.

The casing of an ADCP flow meter is preferably made from titanium alloy. This, in fact, offers great corrosion resistance, which is crucial as the Alaknanda water will be loaded with salts and various minerals. At the same time, it shows a good strength-to-weight ratio, with the effect of durability with relatively easy handling and mounting of the equipment.

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

The following can be identified when choosing equipment for the measurement of current in Alaknanda, For horizontal cross-section measurements, one suitable option is a Horizontal ADCP current profiler (HADCP). It records the flow velocities across a horizontal plane and gives an exceptionally good understanding of the overall flow pattern in a particular reach of the river. In the case of vertical cross-section measurements, a Vertical ADCP is superior because the velocities are profiled from water surface to riverbed through a vertical line.

Coming to frequencies, an ADCP with 600 kHz is good to use in water depths up to roughly 70m. A frequency of 300 kHz is better for deeper reaches where water depth goes 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.