How to Measure Water Current of Alaknanda (Ganga) River?

1. Where is Alaknanda (Ganga) River?

The Alaknanda is a major tributary of the Ganges River. It originates from the Satopanth Glacier and Bhagirathi Kharak Glacier in the Garhwal Himalayas.

This river flows through the hilly regions of Uttarakhand in India. The topography it courses through is a haven of breathtaking natural splendor, abounding in snow - capped peaks, deep valleys, and sylvan forests. The area has rich flora and fauna, including the rare Himalayan species. Along its banks, there are small, idyllic villages that have a unique mountain culture. The local people have a deep connection with the river, relying on it for water supply, fishing, and in some cases, for small-scale hydro-power generation.

While coming down from the heights of the mountains, at places, it cuts into gorges and canyons, making a visually great sight. The Alaknanda joins other main tributaries like Bhagirathi at Devprayag to form Ganges. Its waters have been considered holy in Hinduism, and pilgrims often visit the riverbanks to conduct religious ceremonies and take an immersion in its holy and purifying waters.

2. What does the Flow Rate of Alaknanda (Ganga) look like?

Alaknanda is of great importance to the general water regime of the Ganges. The flow rate of the former is highly dynamic and depends on a number of factors.

The seasonal changes are a major determinant. During the summer months, the snowmelt from the glaciers in its source region significantly raises the flow. The river is then in torrent, carrying a lot of water and sediment. This high-flow period can cause erosion along the riverbanks and reshape the riverbed.

During winter, the flow rate is reduced because of the reduction in snowmelt. In some of these areas, the river becomes calmer and shallower. However, the base flow is maintained by the seepage of the groundwater and the release of water from smaller tributaries and springs. The flow rate also affects the water temperature, which in turn impacts the aquatic life. The flow of Alaknanda is very crucial in maintaining the ecological balance in the Himalayan region, apart from providing water for irrigation and other domestic uses in downstream areas.

3. How to Measure Water Current of Alaknanda (Ganga)?

There are a variety of ways to measure the water current of Alaknanda (Ganga), These are as follows.

Velocity Meter Method: The traditional method by which the velocity is measured uses mechanical or electrical velocity meters. Mechanical velocity meters normally consist of a rotating element, such as a propeller, which rotates with the flow of water. The speed of rotation is proportional to the water velocity. These meters are usually installed at discrete points in the river and are often attached to bridges or fixed structures. This approach requires several installations at different locations and depths to arrive at a comprehensive understanding of the flow. It can also be very labor-intensive and time-consuming, especially in a river like the Alaknanda with a challenging mountainous terrain.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP is an advanced and more efficient way to measure water current. This method uses acoustic waves that measure the velocity of water at many points within a water column simultaneously. This instrument, by emitting sound pulses and analyzing the Doppler shift of the reflected signals, provides a detailed profile of the water current from the surface to the riverbed. The ADCPs can be installed on boats or fixed installations near the river. It will allow a more complete view of the flow pattern in comparison with the method that utilizes a velocity meter.

Buoy Method: Buoys can be fitted with sensors and then released on the surface of Alaknanda. These buoys would then drift along with the flow of the river and, in the process, measure the surface current. The data derived would cover the direction and speed of the surface movement. This method is largely used on the surface layer and will not provide comprehensive details on the flow at other deeper levels in the river.

Of these, the ADCP method is fast gaining favor as it gives very detailed and extensive data with relatively less effort and in a shorter time period.

4. How Do ADCPs Using the Doppler Principle Work?

The ADCPs work on the principle of the Doppler effect. An ADCP profiler while measuring the water current of Alaknanda emits acoustic pulses into water. These pulses interact with particles in water, usually sediment particles, small aquatic organisms, or other suspended matter.

Due to the Doppler effect, the frequency of the reflected sound waves changes when these particles are in motion. If the particles are moving towards the ADCP, the frequency of the reflected waves is higher than the frequency emitted, and vice versa if the movement is away. By precisely measuring this frequency shift and using sophisticated algorithms, the ADCP meter can calculate the velocity of the water at different points within its measurement range.

In addition to velocity measurement, ADCPs can also determine the direction of the flow by analyzing phase differences of the reflected signals from different directions. These detailed velocity profiles show the flow of water at each depth and across different sections of the river.

5. What's Needed for High-Quality Measurement of Alaknanda (Ganga) Currents?

The equipment to be deployed for high-quality measurement of the Alaknanda current should have the following attributes.

The materials of the equipment should be reliable to stand harsh environmental conditions of the river. The Alaknanda has a high sediment load and can have extreme temperature variations due to its mountainous location. A small size and light weight are beneficial, especially for ease of deployment and retrieval in the challenging terrain.

Other crucial aspects include low power consumption. Since most parts of the river are in remote locations, equipment that can be operated for long hours without much power consumption is necessary for continuous and reliable data collection. Cost-effectiveness: To carry out comprehensive measurement across the river, affordable equipment without compromising on quality is required.

The material that can be used in making the casing of an ADCP flow meter is titanium alloy. This alloy has excellent resistance to corrosion, which is vital because the equipment is in contact with river water constantly. It also possesses a good strength-to-weight ratio, which will keep the overall weight of the equipment relatively low while it is encased durably. 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?

To choose the right equipment for current measurement of the Alaknanda, consideration should be given to mainly two factors.

According to the purpose of usage, HADCP is quite suitable for horizontal cross-section measurements. It provides measurements of flow velocity over a horizontal plane and gives insight into how the water is moving laterally within the river. The vertical ADCP current profiler shall be more appropriate for measurements over vertical cross-sections, as it will address the flow velocity from surface to riverbed along a vertical line, which provides insight into the characteristics of the flow in the vertical plane.

Regarding frequency, the depth suitable for different frequencies varies; for instance, an ADCP with 600 kHz is well suited for a water depth within 70 m. It could give satisfactory results in shallow parts of the Alaknanda. Meanwhile, the ADCP frequency of 300 kHz can go to higher water depth of up to 110 m and, therefore is more suitable for deeper parts of the river where the flow patterns are rather complex.

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.