How to measure the water current of the Ghaghara River

1. Where is the Ghaghara River?

The Ghaghara River is a main river in South Asia. It originates from the Tibetan Plateau and flows through Nepal and India.

As it winds through these countries, it runs through quite a variety of landscapes. Through Nepal, it cuts through the foothills of the Himalayas, passing through great sweeps of terracing and small villages. Entering the northern plains of India, it twists through rich farming lands and is deeply part of the rural life there.

Ghaghara is a river of immense importance to the communities it serves. In Nepal, it provides irrigation water for the growth of rice, maize, and wheat, among other crops. In India, the river provides irrigation water in the course of farming in important states like Uttar Pradesh and Bihar. The river also has religious importance and is considered sacred according to Hinduism.

The river supports a very rich and diverse ecosystem. It is the habitat of a variety of fish, including catfish and carp. The riverbanks host large populations of different waterbirds, including kingfishers and egrets. The floodplains and wetlands associated with this river play an essential role in maintaining the ecological balance, offering breeding and feeding grounds to many species.

2. What is the flow rate of the Ghaghara River like?

The Ghaghara River has extreme seasonal variations in flow rate. Normally during the monsoon season that extends from June to September in South Asia, heavy rainfall occurs in the catchment area. It results in a tremendous rise in the flow rate of the river. The swelling of water during this period provides a huge volume of water to the river and raises the flow rate to a few thousand cubic meters per second in certain stretches.

This flow rate decreases during the months of non-monsoon. It nevertheless caries a base flow that is critical for the survival of aquatic life in it, besides being supportive of water-dependent activities including irrigation and maintaining the ecological balance of the associated wetlands. The average may range from a few hundred cubic meters per second during the dry season to the high-flow rates during the monsoon.

3. How to measure water current of the Ghaghara River?

Velocity Meter Method

The conventional technique employs a mechanical or electric velocity meter. These meters are positioned at various locations in the river to directly measure local water velocity. However, complete mapping of the overall water current requires taking several measurements at different depths and sections along the entire width of the river. Since the Ghaghara River is quite long and its conditions prevail differently at different places, this method may be very time-consuming and labor-intensive.

ADCP Method

ADCP current meter is more sophisticated and handy in the measurement of water currents. It detects the movement of water particles with the use of sound waves. By transmitting acoustic signals apart from analyzing the Doppler shift of the reflected signals, it could measure the velocity of water simultaneously at more depths. This gives a very thorough profile of the water current, enabling very accurate gauging of the flow conditions right across the river. The ADCPs can be installed on boats and bridges and even deployed on buoys for continuous monitoring.

Buoy Method

The buoy method consists of buoys with sensors that are put into the river and measure the movement of water around them. They float on the surface and can provide some indication of the surface current. On the other hand, they may not capture the full complexity of the water current as accurately as the other methods-especially when it comes to understanding the variation in the range of velocity at greater depths.

Out of these, the ADCP current profiler is a somewhat advanced and efficient method to measure the water current of the Ghaghara River.

4. How do the ADCPs operating on the Doppler principle work?

The ADCPs work according to the Doppler Principle. When an ADCP flow meter sends an acoustic signal into the water, the sound waves travel in water and interact with moving water particles. Due to the motion of water particles, the frequency changes as reflected sound waves experience a frequency shift caused by the Doppler effect.

If the particles of water are moving towards the ADCP meter, the reflected wave frequency will be higher than the emitted frequency. On the other hand, if the particles of water are moving away from the ADCP, then the reflected wave frequency will fall. The precise measurement of this change in frequency allows the ADCP to calculate the velocity of the water particles at different depths.

From these, the ADCP meter computes the individual velocity measurements at different depths and stitches them together to form a comprehensive profile of the water current. This gives a very good insight into how the water is flowing, not only on the surface but in the vertical section of the river as well.

5. What does high - quality measurement of the Ghaghara river currents require?

Measurements of the current characteristics of the Ghaghara River require certain features for high-quality equipment.

The high material reliability of equipment is expected. It must be able to resist very aggressive conditions of the river environment, including contacts with water and sediment, drastic oscillations of temperature. Monsoon floods of the Ghaghara River and debris-carrying during periods of high flow need resistance from the equipment.

Additionally, a small size, light weight, and low power consumption are desirable. A compact and lightweight device is easier to handle and deploy on a boat or attached to a buoy. Low power consumption ensures that the equipment can operate for extended periods without the need for frequent battery replacements or access to a continuous power source.

Cost-effectiveness is another very important consideration. A less expensive option allows utilization of more measurement equipment for wider monitoring coverage of the river.

In the matter of casing, the ADCP flow meter should be made of a type of titanium alloy. The selection of the material would also have to be highly resistant against corrosion, such as a titanium alloy, crucial when dealing with water bodies, like the Ghaghara River, where the equipment is always in contact with water and other substances that could result in corrosion. It should also be strong, enduring physical impacts and changes in pressure upon its deployment and operation. Besides, the titanium alloy has comparatively low density to add towards the overall objective of keeping the equipment lightweight.

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

The selection of appropriate equipment in the measurement of the current of the Ghaghara River will depend on various aspects.

Based on the Purpose of Use

For horizontal cross-sectional measurement of the current in the river, it would be an HADCP. Horizontal ADCPs are designed to give quite accurate measurements of the water flow in the horizontal plane, which makes it very useful in understanding the overall movement of water across a particular section of the river.

If the focus is on measuring the vertical cross - section of the river current, a vertical ADCP current profiler should be selected. Vertical ADCPs can accurately measure the velocity of water at different depths, providing a detailed profile of how the water flows vertically in the river.

Based on Frequency

Normally, the choice of frequency depends on the depth of water in the Ghaghara River. A 600 kHz ADCP usually works for a water depth up to 70 meters. The 600 kHz frequency offers good resolution and accuracy for measuring water current in reasonably shallow waters.

For deeper waters exceeding 70 meters up to around 110 meters, a more appropriate device is the 300 kHz ADCP. The frequency of 300 kHz can go deeper into the water and still yield reliable measurements of the water current.

There are renowned brands known within the ADCP current meter world that are Teledyne RDI, Nortek, and Sontek. However, for those seeking a cost - effective option with excellent quality, the China Sonar PandaADCP is worth considering. It is made of all - titanium alloy material, ensuring durability and reliability. With its remarkable cost - performance ratio, it provides a great alternative for measuring the water current of the Ghaghara River. 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.