How to Measure Water Current of the Padma River?

1. Where is the Padma?

The Padma is one of the principal rivers in South Asia. It is the main distributary of the Ganges River as it enters Bangladesh. The river is a lifeline for the people of Bangladesh and parts of India.

The Padma flows through the most fertile and densely populated region. The surrounding landscape is constituted of lush green paddy fields, small villages, and busy towns in mosaic form. The river banks are marked by rich varieties of vegetation that thrive in this moist environment. It is part of the delta ecosystem providing a habitat to scores of species of fish, birds, and other wildlife.

The Padma has long constituted part of the cultural and economic backdrop in this region. It forms one of the main transportation routes, with boats of most sizes-from the tiniest fishing vessels to giant cargo barges-transporting goods across its waters. It also supplies irrigation water that allows crops to grow for the people. The Padma is associated with many religious and cultural festivals, which again proves it plays a significant role in the lives of the people.

2. What does the Flow Rate of the Padma look like?

With so many factors coming into play, the flow rate of the Padma is highly variable. The monsoon rains largely determine the flow. During the wet season, normally from June to September, heavy rainfall in the upstream catchment areas causes the river to swell. The flow rate goes up and the current is strong.

The dry season that prevails from October up to May results in low flow rates. During these months, the width of the river may decrease along with the water level in it. However, despite such reductions, the base flow coming from the ground sources and minor tributaries causes the Padma to flow with a considerable speed. Also, the average flow rate does not remain the same throughout the length of the course. The closer towards the upper reaches of the confluence with the Ganges, the flow can be relatively fast. The flow is gradually slower while moving further downstream in the spreading area of the delta.

Human activities that affect the flow rate include water withdrawal for irrigation and the construction of embankments. These and other factors may alter the natural hydrograph of this river and will continue to impact its ecology and associated human communities.

3. How to Measure Water Current of the Padma?

There are several ways of measuring the water current of the Padma. Traditional ones include using floats, whereby a small wooden block or a buoy may be released on the river. Thus, one may get an estimate of the surface current speed by measuring the time taken by that float to travel a known distance. However, this approach has weaknesses in that it is susceptible to winds and some other surface interference.

Another classical method is that of current meters. They are mechanical or electrical devices set in the water at a certain depth, which measure the velocity of water passing through them. They offer more accurate data than floats, but normally are confined to a single point in the water column.

A more sophisticated technique involves the acoustic Doppler current profiler.

3.1 How does a Doppler principle work in an ADCP?

Acoustic Doppler Current Profiler(ADCP) works on the principle of Doppler effect. It transmits the acoustic pulses to the water. These acoustic pulses are reflected by the suspended particles and other elements present in the water. If water is flowing, then its reflected acoustic frequency will be varied.

The ADCP profiler measures this shift in frequency and calculates the velocity of water at different depths using the Doppler formula. It does this by emitting pulses in different directions and at different frequencies, creating a detailed profile of the water current across the water column.

3.2 What is required for high - quality measurement of Padma currents?

For high-quality measurement of the Padma currents, equipment must be reliable. Monsoon flow conditions are harsh, and flow velocities may be high, sediment load is very high, and flooding can occur; therefore, measuring devices must be capable of withstanding such loads.

The equipment should be compact and light. This will be important to ensure the ease of deploying, particularly in remote river alongshore and from boats. It should consume low power. This would ensure that the equipment would operate for an extended period without frequent change of the batteries or provision of an external power source. This equipment should be cost-effective, as there may be the need to carry out measurements on a large scale.

ADCP meter ​with casing in titanium alloy would be useful. The corrosive resistance property of the titanium alloy is very good, which is of prime importance in a water-rich environment like Padma. It is also tough and resilient; therefore, it is able to bear both physical forces from the river current and impacts that may occur. It is lighter in weight, hence convenient during installation and transportation.

3.3 How to Select appropriate equipment for measurement of current?

The equipment to be used would vary depending on the particular requirement of the measurement. HADCP would work for horizontal measurement across a section of the river, which offers a wide view of the current flow in the horizontal plane, useful for understanding the overall flow patterns of the river.

For vertical profile measurements of the current, a vertical ADCP flow meter is more appropriate. It can give detailed information on the velocity at different depths in water, which is very important in the study of stratification and mixing of the water column.

Based on this knowledge, frequency selection for the Padma for sections that are relatively shallow, a depth of 24 to about 70 meters, may consider a 600 kHz ADCP suitable. In deeper parts, up to about 110 meters, a 300 kHz ADCP will be a better choice.

Some of the popular brands of ADCP doppler are Teledyne RDI, Nortek, and Sontek. However, if you are looking for a cost - effective one with good quality, the China Sonar PandaADCP is a good option. It is made of all - titanium alloy, so it can withstand the Padma environment. It also gives a good price - performance ratio. You can visit https://china-sonar.com/ for more details.

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