How to measure Ob's water current?

1. Where is Ob?

Ob is a big river situated in the great area of the Siberian region in Russia. It is considered the longest river in Asia, emerging from the Altai Mountains.

It originates in the mountainous land of Altai, where the glacial meltwaters form its original flow. Further meandering down through Siberia, it covers a wide variety of landscapes-from taiga forests housing a plethora of wildlife, such as bears, wolves, and numerous species of birds, all the way to very extensive plains and marshy areas-building an extremely rich and complicated ecosystem.

Small settlements and larger towns line its banks. These latter have traditionally lived with the river, both on it for fishing and as a means of transportation, and from its supply of water. One of Russia's largest cities, Novosibirsk, stands on the banks of the Ob. The river has played an important role in the development of the region, providing a serious artery for trade and communication.

Eventually, the Ob finds its way into the Arctic Ocean, and the estuary is one important region for different marine species. It is quite remarkable how the river navigates from the mountains to the ocean, shaping landscapes and lives of everything that come in its way.

2. What is the Flow Rate of the Ob River like?

The Ob River has extreme seasonal variations in flow. During spring when the snow and ice are melting both in the Altai Mountains and its huge catchment area, a period of high flow is experienced in this river. By this time, the volume of water increases tremendously, and the current becomes very powerful. This is quite an important season for the river's dynamics since it manages to carry large volumes of sediment and nutrients downstream.

In summer, when the snow melts, the flow rate comes into balance somehow but is still quite high due to constant feeding by tributaries and groundwater, while in autumn the gradual lowering of temperatures gradually reduces the flow rate. During a long and cold winter, the river will have its minimum flow, with parts of it able to freeze up completely.

The flow average is also different along the flow because in the upper reaches of it, closer to its mountain source, the flow can be quite fast due to a much greater gradient. Wherever it is going downstream and flowing over the flatter parts, the rate of flow slows down, with some areas having wider parts of the river.

3. How to Measure Water Current of the Ob River?

There are several ways to measure the water current of the Ob River.

Traditional Methods

Float Method: The most obvious and classical way to estimate the water current is by using floats. A buoyant object, such as a wooden block or plastic bottle, is dropped into the river. It gives an approximation of the surface current speed by being able to know the time taken to cover a known distance. This, on one hand, is not very accurate since wind, waves, or even the shape of the float can introduce errors. It gives only the surface current-the current at different depths is not given by this. 

Current Meters: Both mechanical and electronic meters of current can be employed to measure the speed of water at one point. These are placed in the water at a certain depth and record the speed of water that passes through them. They give more accurate measures than the float method at one point in the water column. But they are limited to that depth and do not give a complete profile of the current in the water column.

Advanced Method - Acoustic Doppler Current Profiler (ADCP)

The ADCP profiler will be an advanced and much more efficient way of measuring the water current in the Ob River.

3.1 How do the ADCPs using the Doppler Principle Work?

ADCP meter is based on the principle of the Doppler effect. The instrument sends out acoustic pulses into the water. These pulses scatter off suspended particles and other materials in the water, including sediment, plankton, and small pieces of debris. A consequence of this is the frequency of the reflected acoustic signals, which changes with the movement of the water.

 This frequency shift, the ADCP measures, and by applying the Doppler formula, it calculates the water's velocity at a range of depths. Since the ADCP flow meter sends out pulses at different frequencies in various directions, a detailed profile of the water current throughout the water column can be produced. This is a far more detailed analysis of the river's current structure compared to the traditional methods of measurement at the surface or a single point within the water column.

3.2 What is necessary to high quality measurement of the Ob River currents? 

For providing high-quality measurements of the Ob river currents, the equipment has to be highly reliable. The Siberian climate is very cold and can be very windy; this may lead to the formation of ice. For such conditions, any device designed for any measurements needed should be strong enough to resist such extreme conditions. 

Equipment should be compact and lightweight. This is important in the aspect of ease of deployment, especially areas along the river that can only be accessed either by boat or through walking in the snow. Low power consumption is the key to ensuring the equipment operates for a long duration without often changing batteries or seeking other external sources of power. Cost-effectiveness could be mentioned as the other critical aspect when large-scale or prolonged measurements of the river dynamics should be realized. 

Utilization of the titanium alloy as ADCP doppler casing material is the significant advantage of the device. This material is highly resistant to corrosion, which is crucially important in water-rich conditions such as those present in Ob River. These other materials would most likely experience corrosion from constant contact with the water, as well as various chemicals and sediments present. Also, the titanium alloy is strong enough to withstand the physical forces of the current of the river and possible impacts from floating logs or other debris. Being lightweight makes such an alloy easy to install and transport, especially when access may not be quite so accessible.

3.3 How to Choose the Right Equipment for Current Measurement? 

The choice of equipment would depend on the particular needs of measurement that one intends to make in the current of the Ob River. 

Horizontal Measurement: In case the requirement is for horizontal measurement across any section of the river, then HADCP would be a decent option. It provides a general overview of the current flow in the horizontal plane; hence, it is good for establishing the general flow patterns of the river. This will be important in understanding the transport of water and sediment across a river and what that current flow would mean in terms of navigation and nutrient distribution. 

For Vertical Profile Measurements: Vertical ADCP current meter would be more appropriately relevant for the measurement of currents for vertical profile analysis. It provides very detailed information concerning the water velocity at different depths, relevant to the study of the stratification and mixing of the water column. It is key to comprehending the distribution of oxygen, temperature, and other properties within the water, besides the study of aquatic organisms' behavior.

 Selection of Frequency: For relatively shallower reaches, like up to approximately 70 meters, a frequency of 600 kHz will suffice. In deeper reaches, approximately 110 meters, the preferred instrument is an ADCP current profiler with a frequency of 300 kHz. This choice depends on the water depth and resolution desired in the current profile.

Well-known brands include Teledyne RDI, Nortek, and Sontek. However, the most cost-effective one with a good quality should be ChinaSonar PandaADCP. The body is made of all-titanium alloy, for strength and against corrosion in the environment of the Ob River. High-class price-to-performance ratio. You are free to go to https://china-sonar.com/.

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