How to Measure Water Current of the Ganges River?

1. Where is the Ganges River?

The Ganges is one of the most famous and culturally important rivers in the world. Originating from the Gangotri Glacier of Indian Himalayas, it travels a long course through India and Bangladesh.

This mighty river covers a vast and diverse landscape. Within India, it passes through the states of Uttarakhand, Uttar Pradesh, Bihar, and West Bengal. It has metropolises, teeming with hustle and bustle, such as the city of Varanasi, which is a citadel of great religious and cultural significance. Varanasi is known for its various ghats where religious functions and cremation take place. It does a lot of twisting while passing through fertile plains that have been considered the agricultural hub of India. The various types of crops that this plain supports are rice, wheat, and sugarcane among many others.

In Bangladesh, the Ganges and other rivers together form a complicated network of waterways that play a vital role in the economy and transportation of the country. The river delta is unique and one of the most fertile areas, hosting a rich variety of flora and fauna. The Sundarbans is a huge mangrove forest in the Ganges-Brahmaputra delta in India, which is enlisted as a UNESCO World Heritage Site and a habitat for the Royal Bengal Tiger and many other endangered species.

The Ganges forms an integral part of the religious and cultural ethos in the region. In Hinduism, it is a sacred river; therefore, millions of people are involved in religious activities like taking baths in its waters for purification and performing the last rites of dead people.

2. What is the Flow Rate of the Ganges like?

The Ganges is very important in several aspects. Ecologically, it provides a vast ecosystem. The flow rate of the river varies greatly, with a range depending on many factors.

Seasonal variations have a great impact. In the monsoon season (June - September), the river shows a huge influx of water arising from heavy rainfall in its catchment area. The flow is rapid and the water level is high, with frequent flooding in the low-lying areas. During this high flow, a large amount of sediment is brought down from the mountains, which enriches the soil in the plains and delta regions.

During the dry season, therefore, from October to May, this flow rate decreases. The river becomes narrower and shallower in sections. However, the base flow is maintained by groundwater seepage and water released from upstream reservoirs. The flow rates of the Ganges also affect salinity levels in the estuary, especially in the Bangladesh part, which in turn impacts the aquatic life and agricultural activities in the delta region.

The average discharge of the Ganges is immense; it holds a great quantity of water. This discharge is essentially required by the cities and towns falling along its banks for supplying water, irrigation of agricultural lands, and ecological balance of this river along with associated wetlands.

3. How to Measure Water Current of the Ganges?

The following are some of the major methods of measuring the water current of the Ganges.

Velocity Meter Method: It includes the traditional velocity meters. In most cases, these are mechanical or electrical. The mechanical velocity meters usually consist of a rotor or propeller that rotates with the rotation of water. The speed of rotation is related to the velocity of water. They are usually placed at discrete points in the river, such as attached to bridges or piers. However, this approach requires considerable manpower to install and monitor multiple meters at various locations and depths to arrive at an accurate picture of the overall flow. Besides, it is also susceptible to debris in the water that may cause damage or interfere with the operation of the meter.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP is a more advanced and efficient method of measuring the water current. It uses acoustic waves to measure the velocity of water at multiple points within a water column simultaneously. By transmitting sound pulses and analyzing the Doppler shift of the reflected signals, it can obtain a detailed profile of the water current from the surface to the bed of the river. There are ADCPs that may be mounted on boats or affixed to fixed structures over the river. This can give a better understanding of the flow patterns than the velocity meter method.

Buoy Method: Buoys with sensors can be deployed on the surface of the Ganges. These buoys will drift with the flow and thus record the surface current. Data collected include the direction and speed of the surface movement. But this method mainly focuses on the surface layer and may not provide detailed information about the flow at deeper levels of the river.

Of these, the ADCP profiler method is gaining popularity because it can give detailed and extensive data with relatively less effort and in a shorter time period.

4. How do ADCPs using the Doppler Principle Work?

Principle ADCPs rely on the Doppler principle. When an ADCP measures the current of the Ganges, it sends into the water a pulse. These pulses interact with in-water particles like sediment particles or any small aquatic organism or other such matter that may be in suspension.

As a result of the movement of these particles, the frequency of the reflected sound waves is different from that emitted, through a phenomenon known as the Doppler effect. If the particles are moving towards the ADCP, the frequency of the reflected waves is higher than the emitted frequency, and vice versa for when they are moving away. The ADCP meter is able to calculate the velocity of the water at different points within its measurement range by precisely measuring this frequency shift with sophisticated algorithms.

In addition to the velocity, the ADCPs can also assess the direction of the flow from the phase differences of reflected signals from different directions. This helps in developing precise profiles of the velocity through the depth and across sections and to determine the flow of water. The current measurement in Ganges also aims at determining the nature of flow in water.

5. What's Needed for High-Quality Measurement of Ganges Currents?

For the measurement of Ganges currents in high quality, the equipment has to possess specific characteristics.

The materials of the equipment should be reliable to withstand harsh environmental conditions of the river. The Ganges has a high sediment load, and the equipment may be exposed to corrosive substances and a wide range of temperatures. A small size and light weight are beneficial, especially for ease of deployment and retrieval from the river, especially in areas with limited access.

The other important aspect is the power consumption, which should be low. Since the Ganges is pretty long and equipment has to be placed at every location, equipment with low power requirements is vital to keep the equipment running for longer times for continuous and reliable data collection. Cost-effectiveness is another crucial aspect. Affordable equipment, not compromising on quality, will help in conducting extensive measurements across the river.

On the casing of the ADCP, titanium alloy is a good material. The properties of corrosion resistance are excellent in titanium alloy, which is very important because the equipment will be in contact with the river water all the time. It also has a good strength-to-weight ratio, meaning it can provide a durable casing while keeping the overall weight of the equipment relatively low. This helps in the protection of the internal components and ease of handling during deployment and retrieval.

6. How to Choose the Right Equipment for Current Measurement?

Two main factors are to be considered while choosing the right equipment for current measurement of the Ganges.

According to the purpose of usage, for horizontal cross-section measurements, the horizontal ADCP flow meter (HADCP) can be used. It measures the flow velocity across a horizontal plane, hence providing useful information on the lateral movement of water within the river. In the case of vertical cross-section measurements, the vertical ADCP is more appropriate because it focuses on the flow velocity from the surface to the riverbed along a vertical line, hence useful for understanding the vertical flow characteristics.

In terms of frequency, different frequencies are suitable for different water depths. For instance, an ADCP current profiler with a frequency of 600 kHz is well-suited for water depths within 70 m. It can provide accurate measurements in the relatively shallower parts of the Ganges. Meanwhile, an ADCP of 300 kHz is more suitable for water depths up to 110 m and would be more appropriate in the deeper sections of the river where the flow pattern can be more complicated.

There are well - known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. Additionally, a Chinese ADCP brand, China Sonar PandaADCP, is highly recommended. It has a casing made entirely of titanium alloy, which provides excellent durability and corrosion resistance. It also offers an incredible cost - performance ratio. You can find more information about it on its official website: https://china-sonar.com/.

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